imperial college london department of earth science and … · 2015-06-26 · formatted: font: 12...

IMPERIAL COLLEGE LONDON

Department of Earth Science and Engineering

Centre for Petroleum Studies

Integration of Residual Hydrocarbon Saturations

From Well Logs Identified Swept Zones Identified in Well Logs with Relative

Permeability

aAnd Core Saturation Data

By

Giri Aridita

A report submitted in partial fulfilment of the requirements for

the MSc and/or the DIC.

September 2010

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DECLARATION OF OWN WORK

I declare that this thesis

INTEGRATION OF RESIDUAL HYDROCARBON SATURATIONS FROM WELL LOGS

IDENTIFIED SWEPT ZONES IDENTIFIED IN WELL LOGS WITH RELATIVE

PERMEABILITY AND CORE SATURATION DATA

is entirely my own work and that where any material could be construed as the work of others,

it is fully cited and referenced, and/or with appropriate acknowledgement given.

Signature:

Name of student: Giri Aridita

Name of Imperial College supervisor: Dr. Matthew D. Jackson

Name of company supervisor: Fabrizio Conti (Maersk Oil North Sea UK Limited)

Stephen Milner (Maersk Oil North Sea UK Limited)

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Abstract

The Central North Sea Asset of Maersk Oil UK Ltd. (MOUK) spreads over several oil fields

producing from Paleogene period of clastic reservoirs, where most of the fields are under water injection

or active aquifer support. As the dynamics effect of production and water injection, mMoving oil-water

contacts due to production effects has left behind some residual oil saturation to water (Sorw). The correct

quantification of Sorw is necessary for estimating recoverable reserves, as well as enabling more accurate

reservoir simulation. Sorw value can be acquired from different types of measurement which resultbut

can inconsistent might be obtained due to the uncertainties attributed in each method.

This study aims to compare different methods and reduce the uncertainty in Sorw values in four fields

which are producing from the prolific Balder Massive Sandstones. The fields of interest are located in

different blocks of quad 9 in Central North Sea area, namely Gryphon Maclure, Tullich and Harding

where resemblances in rock and fluid properties are observed.

Several methods based on available open hole log and core analysis dataset were taken to calculate

Sorw. Open hole logs are used to calculate Sorw in the swept zone using Archie equation, in which the

electrical properties are derived from Special Core Analysis (SCAL) data. Uncertainties in Archie

parameters are also captured to generate a range of values of Sorw from log analysis, and core saturation

data from Dean Stark analysis is used to verify log-derived saturation.

Oil-water relative permeability data from unsteady-state test are used to find Sorw values whenat zero

oil relative permeability have been achieved. Validity of the results from each core sample is investigated

to exclude samples that are affected by capillary effect and end effect that overestimate the Sorw value.

Coreflood test result was also analyzed to find Sorw after laboratory waterflooding test, and it shows the

relation of oil saturation to the amount of pore volume (PV) water injected. To see the extent of PV water

injected to Sorw in reservoir condition, an attempt to replicate Buckley Leverett-derived plot

displacement to from the log data was made. The result then compared to core derived Buckley Leverett

analysis for verification. An observation to the existing simulation model result also indicates that the

relation exists in the case of advancing oil-water contact.

Archie equation is found to be reliable in clean Balder Massive Sandstone shown by previous in-house

study,. and the lLog derived Sorw give a most likely range of 10-20% with a variation of range observed

in different well samples. Oil-water relative permeability analysis comes up with the range of 16-30%

with the mode of 20%. Core flood data shows that Sorw in the range of 10-30% and is inversely

proportional to the amount of water injected. It also indicates that true residual oil saturation in Balder

Formation might not be achieved until the injection of many PV of water. This could be interpreted that

observed Sorw will be reduced as the oil-water contact is advancing.

After data reconciliation, the selected values of Sorw are 10%, 20%, and 30% for the P10, P50, and

P90 respectively. Each value then is used to re-scale existing relative permeability data set to see how

different Sorw will impact the ultimate oil recovery. The simulation model then run to make prediction

until the end of oil production in 2018 and it change the ultimate recovery of ±6 % or -5.5 to +8 MMSTB

in the remaining reserves.

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Integration of Residual Hydrocarbon Saturations From Well Logs Giri Aridita Identified Swept Zones With Relative Permeability and Core Saturation Data MSc in Petroleum Engineering 2009/2010

I List of Figures

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LIST OF FIGURES

Figure 1 Gryphon Simulation Model ..................................................................................... Error! Bookmark not defined.3

Figure 2 Cross Section of Gryphon Simulation Model Showing Movement in OWC .... Error! Bookmark not defined.3

Figure 4 Comparison of Log and Core Porosity.................................................................. Error! Bookmark not defined.9

Figure 9 Kv Distributions in Sector Model .......................................................................... Error! Bookmark not defined.12

Figure 12 Sor Reconciliation ................................................................................................ Error! Bookmark not defined.12

Figure 11 Relative Permeability Data and Curve-fitted Corey Model ............................ Error! Bookmark not defined.12

Figure 13 Relative Permeability Model for Flow Simulation ............................................ Error! Bookmark not defined.12

Figure 14 Impact of Different Sor to Ultimate Oil Recovery ............................................ Error! Bookmark not defined.13

Figure 15 Sensitivity Analysis of Archie Equation ............................................................ Error! Bookmark not defined.13

Figure 16 Effect of Petrophysical Properties to Sor and Corey Exponents .................. Error! Bookmark not defined.14

Figure 1 Gryphon Simulation Model ......................................................................................................................................... 3

Figure 2 Cross Section of Gryphon Simulation Model Showing Movement in OWC ........................................................ 3

Figure 3 Relative Permeability Curve Refinement Work Flow .............................................................................................. 7

Figure 4 Comparison of Log and Core Porosity...................................................................................................................... 9

Figure 5 Residual Oil Saturation in Open Hole Log ............................................................................................................. 10

Figure 7 Sorw Histogram from Relative Permeability Analysis .......................................................................................... 10

Figure 8 Laboratory Core Water Flood Test Result ............................................................................................................. 11

Figure 9 Buckley Leverett Analysis on Refined Water-Oil Relative Permeability Data ................................................... 11

Figure 10 Sector Model Showing Decreasing Oil Saturation in Rising Oil Water Contact ............................................. 11

Figure 11 Kv Distribution in Sector Model ............................................................................................................................. 11

Figure 12 Relative Permeability Data and Curve-fitted Corey Model ................................................................................ 12

Figure 13 Sor Reconciliation .................................................................................................................................................... 12

Figure 14 Relative Permeability Model for Flow Simulation ................................................................................................ 12

Figure 15 Impact of Different Sor to Ultimate Oil Recovery ................................................................................................ 12

Figure 16 Partial Error Contribution from Archie Constant .................................................................................................. 13

Figure 17 Effect of Petrophysical Properties to Sor and Corey Exponents ...................................................................... 13

Fig. 1 Field location map (right) and schematics of fields boundaries (left) ........................................................................ 3

Fig. 2 Cross section of gryphon simulation model showing movement in OWC in the forms of water cusping around

horizontal production wells and moving free water level at a larger scale. ......................................................................... 4

Fig. 3 Reservoir wettability data measured from various type of core plugs. Fresh state plugs show a variety of

wettability state from strongly oil wet to weakly water wet .................................................................................................... 4

Fig. 4 Relative permeability curve refinement work flow as suggested by Stiles [2004] from raw data ......................... 8

Fig. 5 Comparison of log and core porosity ........................................................................................................................... 10

Fig. 6 Sorw Histogram from Relative Permeability Analysis ............................................................................................... 10

Fig. 7 Residual oil saturation in open hole log ...................................................................................................................... 11

Fig. 9 Buckley Leverett analysis on refined water-oil relative permeability data from (a) all available data and (b)

validated data from screening criteria superimposed with replicated log-derived curve ................................................ 12

Fig. 10 Kv distributions in sector model ................................................................................................................................. 12

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II Table of Contents - AppendicesList of Tables

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Fig. 11Sector model from Gryphon full field model showing decreasing oil saturation in the swept zones as oil water

contact is increasing .................................................................................................................................................................. 12

Fig. 12 Sor reconciliation from different measurements ...................................................................................................... 13

Fig. 13 Relative Permeability Data and Curve-fitted Corey Model ..................................................................................... 13

Fig. 14 Relative Permeability Model for Flow Simulation .................................................................................................... 13

Fig. 15 Impact of different sor to ultimate oil recovery ......................................................................................................... 14

Fig. 16 Sensitivity analysis of archie equation ...................................................................................................................... 15

Fig. 1 Effect of petrophysical properties to Sor and Corey exponents…………………………………………………15

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III List of Figures




LIST OF TABLES

Table 1 Residual Oil Saturation in Different Fields ................................................................................................................. 2

Table 2 Summary of Fluid Contacts ......................................................................................................................................... 3

Table 3 Summary of Rock and Fluid Properties ..................................................................................................................... 3

Table 4 Number of Samples Available from Various SCAL Analyses ............................................................................... 54

Table 5 Values of Corey Exponent for Different Type of Wettability .................................................................................. 65

Table 6 Range of Values for Screening Criteria ................................................................................................................... 87

Table 7 Archie Equation Parameters .................................................................................................................................... 109

Table 8 Uncertainties in Archie Parameters ........................................................................................................................ 109

Table 9 Residual Saturation from Open Hole Log .............................................................................................................. 109

Table 10 Relative Permeability End Points for Sensitivity Analysis ............................................................................... 1412


IV Table of Contents - AppendicesList of Tables


TABLE OF CONTENTS - APPENDICES

APPENDIX 1: Critical Literature Review 11

A1.1 SPE 3791 - Determination of Residual Oil Saturation After Water flooding

44

A1.2 SPE 14887 - Evaluation and Comparison of Residual Oil Saturation Determination Techniques

55

A1.3 SPE 30763 - Dependence of Waterflood Remaining Oil Saturation on Relative Permeability, Capillary Pressure, and

Reserrvoir Parameters in Mixed Wet Turbidite Sands 66

A1.4 SPE 19851 - Field Wide Variations in Residual Oil Saturation in a Sea Sandstone Reservoir

77

A1.5 SPE 88628 Residual Oil Saturation Analysis of The Burgan Fromation in the Greater Burgan Field, Kuwait.

88

A1.6 SPE 16471 Wettability Literature Survey-Part 6: The Effects of Wettability on Waterflooding

99

A1.7 SPWLA 1986-vXXVIIn5a3 Sensitivity Analysis of The Parameters In Archie''s Water Saturation Equation

1010

A1.8 SPWLA 2004-UUU EVALUATION OF RESIDUAL OIL SATURATION IN THE BALMORAL FIELD (UKCS)

1111

A1.9 SPE 39038 Optimal Design and Planning for Laboratory Corefloods

1212

A1.1010 SPE 17686 Residual Oil Saturations Determined by Core Analysis

1313

A1.11 SPE 3785 Reservoir Waterflood Residual Oil Saturation from Laboratory Tests

1414

A1.12 SPE 3786 Core and Log Determination of Residual Oil After Waterflooding - Two Case Histories.

1515

A1.13 SPE 3795 Determination of Residual Oil Saturation From Time-Lapse Pulsed Neutron Capture Logs in a Large

Sandstone Reservoir. 1616

A1.14 SPE 77545 A Unified Theory on Residual Oil Saturation and Irreducible Water Saturation.

1717

A1.15 SPE 22903-MS Determining Effective Residual Oil Saturation for Mixed Wettability Reservoirs: Endicott Field, Alaska.

1818

APPENDIX 2: Field Description Figures

1919

APPENDIX 3: Log Analysis

2727

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V Table of Contents - Appendices




APPENDIX 4: Core Analysis

2929

APPENDIX 5: Relative Permeability Data Refinement

3232

APPENDIX 6: Buckley Leverett Calculations

3838

APPENDIX 7: Impact of SORW to Recovery Prediction and History Match

3939

APPENDIX 1: Critical Literature Review 1

A1.1 SPE 3791 - Determination of Residual Oil Saturation After Water flooding

4

A1.2 SPE 14887 - Evaluation and Comparison of Residual Oil Saturation Determination Techniques

5

A1.3 SPE 30763 - Dependence of Waterflood Remaining Oil Saturation on Relative Permeability, Capillary Pressure, and

Reservoir Parameters in Mixed Wet Turbidite Sands 6

A1.4 SPE 19851 - Field Wide Variations in Residual Oil Saturation in a Sea Sandstone Reservoir

7

A1.5 SPE 88628 Residual Oil Saturation Analysis of The Burgan Fromation in the Greater Burgan Field, Kuwait.

8

A1.6 SPE 16471 Wettability Literature Survey-Part 6: The Effects of Wettability on Waterflooding

9

A1.7 SPWLA 1986-vXXVIIn5a3 Sensitivity Analysis of The Parameters In Archie''s Water Saturation Equation

10

A1.8 SPWLA 2004-UUU EVALUATION OF RESIDUAL OIL SATURATION IN THE BALMORAL FIELD (UKCS)

11

A1.9 SPE 39038 Optimal Design and Planning for Laboratory Corefloods

12

A1.10 SPE 17686 Residual Oil Saturations Determined by Core Analysis

13

A1.11 SPE 3785 Reservoir Waterflood Residual Oil Saturation from Laboratory Tests

14

A1.12 SPE 3786 Core and Log Determination of Residual Oil After Waterflooding - Two Case Histories.

15

A1.13 SPE 3795 Determination of Residual Oil Saturation From Time-Lapse Pulsed Neutron Capture Logs in a Large

Sandstone Reservoir. 16

A1.14 SPE 77545 A Unified Theory on Residual Oil Saturation and Irreducible Water Saturation.

17


VI Table of Contents - AppendicesList of Tables


A1.15 SPE 22903-MS Determining Effective Residual Oil Saturation for Mixed Wettability Reservoirs: Endicott Field, Alaska.

18

APPENDIX 2: Field Descriptions 19

Archie Constants Calculation 25

Log Analysis 27

27

Core Analysis 29

Relative Permeability Data Refinement 32

Buckley Leverett Calculations 38

Impact of SORW to Recovery Prediction and History Match 39

APPENDIX 1: APPENDIX 1: Critical Literature Review 1

A.1 1 SPE 3791 Determination of Residual Oil Saturation After Water flooding 4

TABLE OF CONTENTS - APPENDICES

APPENDIX - 1 Critical Literature Review 1

APPENDIX - 2 Field Descriptions 2

APPENDIX - 3 Archie Constants Calculation 3

APPENDIX - 4 Relative Permeability Data Refinement 4

APPENDIX - 5 Core Analysis Procedures 5

APPENDIX - 6 Buckley Leverett Calculations 6

APPENDIX - 7 Impact of SORW to Recovery Prediction and History Match 7

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VII List of FiguresTable - Appendicesx




LIST OF FIGURES - APPENDICES

Figure A 1 Net Sand Map of Gryphon Area with the Locations of Cored Wells ......................................................................... 19

Figure A 2 Core photograph of Well 9/18b-7 Showing Oil Bearing Sandstone .......................................................................... 19

Figure A 3 Type Log of Gryphon Area Showing Balder Massive Sandstone .............................................................................. 20

Figure A 4 Composite RFT Data from Gyphon ........................................................................................................................... 21

Figure A 5 Porosity Permeability Cross Plot of Balder Massive Sandstone ................................................................................ 21

Figure A 6 Kv/Kh Cross Plot of Balder Massive Sandstone ........................................................................................................ 21

Figure A 7 North South Schematic Cross Section of Gryphon Field ........................................................................................... 22

Figure A 8 West East Seismic Cross Section of Gryphon Field .................................................................................................. 22

Figure A 9 North South Schematic Cross Section of Harding and Tullich Field ......................................................................... 23

Figure A 10 North South Schematic Cross Section of Maclure Field .......................................................................................... 23

Figure A 11 Histogram of Core Derived Cementation Factor ..................................................................................................... 25

Figure A 12 Histogram of Core Derived Saturation Exponent .................................................................................................... 25

Figure A 13 Histogram of Log Derived Apparent Water Resistivity (Rwa) ................................................................................ 26

Figure A 14 Harding Well 9/23b-A29 Open Hole Log ................................................................................................................ 27

Figure A 15 Gryphon Well 9/18b-30A Open Hole Log ............................................................................................................... 28

Figure A 18 Pie Chart of the Number of Plugs for Different SCAL Analysis in Harding Field .................................................. 29

Figure A 17 Pie Chart of the Number of Plugs for Different SCAL Analysis in Gryphon Field ................................................. 29

Figure A 16 Pie Chart of the Number of SCAL Wells ................................................................................................................. 29

Figure A 19 Pie Chart of the Number of Plugs for Different SCAL Analysis in Maclure Field .................................................. 30

Figure A 20 Pie Chart of the Number of Plugs for Different SCAL Analysis in Tullich Field ................................................... 30

Figure A 21 Histogram of Oil Saturation From Dean Stark Analysis .......................................................................................... 31

Figure A 21 Workflow of Buckley Leverett Analysis to Calculate Oil Saturation as A Function of PV Water Sweep .............. 38

Figure A 23 Comparison of Field Water Production Rate from Different Sor Cases with Actual Production Rate .................... 39

Figure A 22 Comparison of Field Oil Production Rate from Different Sor Cases with Actual Production Rate ......................... 39

Figure A 25 Comparison of Field Gas Production Rate from Different Sor Cases with Actual Production Rate ....................... 40

Figure A 24 Comparison of Field Water Cut Production Rate from Different Sor Cases with Actual Production Rate ............. 40

Figure A 1 Net Sand Map of Gryphon Area with the Locations of Cored Wells ......................................................................... 19

Figure A 2 Core photograph of Well 9/18b-7 Showing Oil Bearing Sandstone .......................................................................... 19

Figure A 3 Type Log of Gryphon Area Showing Balder Massive Sandstone .............................................................................. 20

Figure A 4 Composite RFT Data from Gyphon ........................................................................................................................... 21

Figure A 5 Porosity Permeability Cross Plot of Balder Massive Sandstone ................................................................................ 21

Figure A 6 Kv/Kh Cross Plot of Balder Massive Sandstone ........................................................................................................ 21

Figure A 7 North South Schematic Cross Section of Gryphon Field ........................................................................................... 22

Figure A 8 West East Seismic Cross Section of Gryphon Field .................................................................................................. 22

Figure A 9 North South Schematic Cross Section of Harding and Tullich Field ......................................................................... 23

Figure A 10 North South Schematic Cross Section of Maclure Field .......................................................................................... 23

Figure A 11 Histogram of Core Derived Cementation Factor ..................................................................................................... 25

Figure A 12 Histogram of Core Derived Saturation Exponent .................................................................................................... 25


VIII List of Figures - Appendices

Figure A 13 Histogram of Log Derived Apparent Water Resistivity (Rwa) ................................................................................ 26

Figure A 14 Harding Well 9/23b-A29 Open Hole Log ................................................................................................................ 27

Figure A 17 Pie Chart of the Number of Plugs for Different SCAL Analysis in Harding Field .................................................. 29

Figure A 16 Pie Chart of the Number of Plugs for Different SCAL Analysis in Gryphon Field ................................................. 29

Figure A 18 Pie Chart of the Number of SCAL Wells ................................................................................................................. 29

Figure A 18 Pie Chart of the Number of Plugs for Different SCAL Analysis in Maclure Field .................................................. 30

Figure A 19 Pie Chart of the Number of Plugs for Different SCAL Analysis in Tullich Field ................................................... 30

Figure A 20 Histogram of Oil Saturation From Dean Stark Analysis .......................................................................................... 31

Figure A 21 Workflow of Buckley Leverett Analysis to Calculate Oil Saturation as A Function of PV Water Sweep .............. 38

Figure A 23 Comparison of Field Water Production Rate from Different Sor Cases with Actual Production Rate .................... 39

Figure A 22 Comparison of Field Oil Production Rate from Different Sor Cases with Actual Production Rate ......................... 39

Figure A 25 Comparison of Field Gas Production Rate from Different Sor Cases with Actual Production Rate ....................... 40

Figure A 24 Comparison of Field Water Cut Production Rate from Different Sor Cases with Actual Production Rate ............. 40


IX List of Table - Appendices

LIST OF TABLES - APPENDICES

Table A 1 Reservoir Oil Properties..............................................................................................24

Table A 2 Formation Water Properties……………………………………………………………….24

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Abstract

The Central North Sea Asset of Maersk Oil UK Ltd. (MOUK) spreads over several oil fields producing from Paleogene

period of clastic reservoirs, where most of the fields are under water injection or active aquifer support. As the dynamics effect

of production and water injection, moving oil-water contacts has left behind some residual oil saturation to water (Sorw). The

correct quantification of Sorw is necessary for estimating recoverable reserves, as well as enabling more accurate reservoir

simulation. Sorw value can be acquired from different types of measurement which result can inconsistent due to the

uncertainties attributed in each method.

This study aims to compare different methods and reduce the uncertainty in Sorw values in four fields which are producing

from the prolific Balder Massive Sandstones. The fields of interest are located in different blocks of quad 9 in Central Sea

area, namely Gryphon Maclure, Tullich and Harding where resemblances in rock and fluid properties are observed.

Several methods based on available open hole log and core analysis dataset were taken to calculate Sorw. Open hole logs

are used to calculate Sorw in the swept zone using Archie formequation, in which the electrical properties are derived from

Special Core Analysis (SCAL) data. Uncertainties in Archie parameters are also captured to generate a range of values of Sorw

from log analysis, and core saturation data from Dean Stark analysis is used to verify log-derived saturation.

Oil-water relative permeability data from unsteady-state test are used to find Sorw values at zero oil relative permeability.

Validity of result from each core sample is investigated to exclude samples that affected by capillary effect and end effect that

overestimate the Sorw value. Coreflood test result was also analyzed to find Sorw after laboratory waterflooding test, and it

shows the relation of oil saturation to the amount of pore volume (PV) water injected. To see the extent of PV water injected to

Sorw in reservoir condition, an attempt to replicate Buckley Leverett displacement to log data was made. The result then

compared to core derived Buckley Leverett analysis for verification. An observation to the existing simulation model result

also indicates that the relation exists in the case of advancing oil-water contact.

Archie formequation is found to be reliable in clean Balder Massive Sandstone, and the log derived Sorw give a most likely

range of 10-20% with a variation of range observed in different well samples. Oil-water relative permeability analysis comes

up with the range of 16-30% with the mode of 20%. Core flood data shows that Sorw in the range of 10-30% and is inversely

proportional to the amount of water injected. It also indicates that true residual oil saturation in Balder FormFormation might

not be achieved until the injection of many PV of water. This could be interpreted that observed Sorw will be reduced as the

oil-water contact is advancing.

After data reconciliation, the selected values of Sorw are 10%, 20%, and 30% for the P10, P50, and P90 respectively. Each

value then is used to re-scale existing relative permeability data set to see how different Sorw will impact the ultimate oil

recovery. The simulation model then run to make prediction until the end of oil production in 2018 and it change the ultimate

recovery of ±6 XX-XX% andor -XX-XX5.5 to +8 MMSTB in the remaining reserves.

Introduction

Residual oil saturation (Sor) is an important parameter for reserves evaluation and reservoir simulation. It is also an

indicator the potential of a tertiary recovery being applied in the respective field. Review on Sor is normally carried out in a

field under secondary recovery of waterflooding, where some amount of oil is left behind the flood front. The same

phenomenon of residual oil saturation to water (Sorw) is also observed in the swept zone of advancing oil -water contact. An

accurate determination of Sor could provide the basis of refining the recovery factor prediction and possibility to increase

field’s reserve estimation.

The term of residual oil saturation has a loose definition as pointed out by several author such as [Al-Sabea [, 2004],

[Chang, [1988], [Hirasaki, [1996], [Strange, [1972] and [Valenti, [2002]. It is defined as (a) the fraction of the pore volume

that contains oil which cannot be displaced by immiscible fluid [Strange, [1972]15

. (b) The lowest oil saturation that a reservoir

INTEGRATION OF RESIDUAL HYDROCARBON SATURATIONS FROM WELL LOGS IDENTIFIED SWEPT ZONES IDENTIFIED IN WELL LOGS WITH RELATIVE PERMEABILITY AND CORE SATURATION DATA

Student name: Giri Aridita

Imperial College supervisor: Dr. Matthew D. Jackson

Company supervisor(s): Fabrizio Conti (Maersk Oil North Sea UK Ltd.)

Stephen Milner (Maersk Oil North Sea UK Ltd.)

Imperial College

London

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XII List of Tables - Appendicesx

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Field Code Changed

can technically achieved in a given recovery mechanism1

[Al-Sabea, [2004]. (c) It might also be defined according to the

physical

2

condition that resulted in such as saturation at which the oil relative permeability reaches zero [Hirasaki [, 1996]. (d) In

laboratory core measurement it is defined as final saturation value at the end of displacement, (e) whereas on the field level it

is defined as the saturation in the swept zone, which relates the Sorw to the amount of water sweeping the reservoir16

.Another

perspective is that (f) the displacement.

(e) On the field level it is defined as the saturation in the swept zone, which relates the Sorw to the amount of water

sweeping the reservoir [Chang, [1988]. Another perspective is that (f) the remaining oil saturation is a measure of how far the

process has travelled along the Kro curve at the time it is terminated. In this study, the term of residual oil saturation refers to

the saturation at the end of displacement process both in the reservoir and the laboratory.

Previous author16

which utilized Pulsed Neutron Capture (PNC) log to monitor saturation behind casing in a naturally

water swept zonesfield under water flood. The result shows that after the water swept an interval, the oil saturation would

continue to decrease over time as the water is sweeping over an interval [Syed, [1991]. Another study shows that residual oil

saturation in mixed wettability reservoirs is a strong function of pore volume (PV) water injected [Wood, [1991]. This is

because oil is only trapped in the large oil-wet pores and creates connected paths along the pore walls. Thus oil permeability

will always exist even in the very low oil saturation, allowing oil to be displaced as more PV of water is injected.

One way to calculate Sorw is by calculating oil saturation from open hole log data in the swept zone, which is considered

as in-situ single well measurement [Chang, [1988]. However the true residual oil saturation is frequently not met until a

reservoir has been swept for many years. The accuracy of this method is largely affected by the value of the electrical

constants in water saturation equation, porosity, and type of resistivity tool being used [Al-Sabea [, 2004].

Special Core Analysis (SCAL) provides different type Sorw measurements which normally include core flood analysis,

relative permeability measurement, and centrifuge capillary pressure measurement. Routine Core Analysis (RCAL) study also

provides saturation measurement by means of Dean Stark analysis. Frequently different methods of measurement do not yield

consistent answers; therefore comparison of results is an alternative for Sorw evaluation.

Laboratory displacement tests provides an estimate of residual oil saturation after water flooding, but the results may vary

depends on test condition, sample condition, and procedure which is taken. These issues increase the uncertainty of results,

and validity of the test become an important concern before taking the value of Sorw as a reference. In an oil-water

displacement test it is necessary to mimics actual reservoir condition by carry out the test in reservoir temperature and using

reservoir fluids [Kennaird, [1988]. Limitation in core plug size and available tool sometimes made the test could only be

conducted for a narrow range of measurement which makes the result become inaccurate.

There is a number of publications which attempted to integrate Sorw from core and log analysis data. Al Sabea ([2004])

investigated Sorw in a waterflooded Burqan Field in Kuwait by comparing open hole log data, cased hole log data, and core

flood data. He also investigated different Sorw values for different rock type and related the change in Sorw with time using

pulse neutron log data. Chang [(1988]) compared several methods of Sorw measurement both by single well and multi well

techniques. Cordiner [(1972]) supplemented core and log analysis with material balance method. Strange [(1972]) investigated

the effect of different coring methods to Sorw and compare it with open hole log results. All authors found a good agreement

between core and log data, however the accuracy of results may varies depend on the number of rock types and reservoir

heterogeneity.

Currently, various studies in Maersk Oil UK Ltd. (MOUK) only rely on core derived Sorw, and none of the effort ever

consider an integration and reconciliation of various data sources and relate the remaining oil saturation with the amount of

water sweep. Table 1 summarises the Sorw values from water-oil relative permeability end points in the fields of interest.

This study aims to compare Sorw values obtained from different methods after reducing uncertainties attributed in each

method. The Sorw comes from open hole logs, unsteady state oil-water relative permeability test, and waterflood test, and

Dean Stark analysis. Emphasized on the limitation for each method is presented and relation of Sorw to pore volume (PV) of

water injected is investigated. The deliverable result is a new range of Sorw values which will be implemented to the existing

reservoir simulation model to re-forecast recoverable reserves before gas cap blowdown in 2018..

Field description and geology

Gryphon area consists of the main Gryphon field with the surrounding smaller fields which are Maclure, Tullich and

Harding. All the fields produce from Palaeocene age Balder FormFormation which comprises of clean, well-sorted, fine to

medium grain, and poorly cemented sandstone as described by [Newman, [1993] with joined estimated P50 STOIIP of 600

MMstb. It is located in the South Viking Graben Area of the Central North Sea Block 9/18b, 9/18a, 9/23a, and 9/23b

Table 1 Residual Oil Saturation in Different Fields

Field Sorw Range Normalized Sorw Source

Tullich 0.22 - 0.38 0.25 Core

Gryphon 0.09 - 0.44 0.24 Core

Harding 0.24 - 0.26 0.26 Core

Maclure 0.18 - 0.35 0.27 Core

Field Sorw Range Normalized Sorw Source

Tullich 0.22 - 0.38 0.25 Core

Gryphon 0.09 - 0.44 0.24 Core

Harding 0.24 - 0.26 0.26 Core

Maclure 0.18 - 0.35 0.27 Core

Formatted Table

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3

Gryphon

Harding

Tullich

MaclureGryphon

Harding

Tullich

Maclure

respectively, 320 km east of Aberdeen. The first hydrocarbon accumulation was discovered by exploration well 9/18b-7 in

Gryphon prospect in 1987 that encountered 405ft of gross reservoir with 325ft net hydrocarbon pay-zone. Further exploration

subsequently discovered smaller oil accumulation in Maclure and Tullich, and Harding in 1991.

All the fields are deposited in turbidite environments with a combination of stratigraphic and dip closure trap overlain by

gas cap and underlain by large aquifer. Fluid contacts are observed from large numbers of well logs and confirmed by RFT

data prior to production as shown in Appendix II.

Previous study shows that Gryphon, Tullich and Harding are underlain by the same aquifer which is shown by water

compositional analysis and pressure gradient. Meanwhile Maclure is underlain by different and weaker aquifer which is not

connected to Gryphon’s. Despite having separate contacts all field are hydrostatistically balanced and it was observed that

there is direct pressure communication through the gas cap. Table 2 summarise original fluid contacts in all fields.

Table 2 Summary of Fluid Contacts

Table 2 Summary of Fluid Contacts

The majority of reserves in the Gryphon area are contained in high quality Balder Massive Sandstone, with some contained

in the injection wings, a geological feature where the original sand body are remobilised. The unconsolidated sandstone

resulted high porosity and high permeability reservoir with average net to gross ratio up to 98% and Kv/Kh ratio close to unity

as shown in Appendix II. Cross-plot of core porosity and permeability which shown in Appendix II shows the trend of single

rock type exist in the reservoir. Balder Sandstone contains saturated heavy oil with high viscosity which range from 20-26

API with viscosity from the lowest 3.2 cP in Tullich to the highest 7.5 cP in Gryphon. Typical reservoir and fluid properties

for Balder FormFormation are summarized in table 3.

Table 3 Summary of Rock and Fluid Properties

Field Por (%) k (D) N/G (%)

Gross Thickness (ft) API

Viscosity (cp)

GOR (scf/bbl)

Bubble Point (deg F)

Tullich 30 1 98 30-59 26 3.2 316 2450

Gryphon 33 6 98 400-650 21.5 7.5 270 2510

Harding 35 8-10 99 250 22 5 238 2480

Maclure 33 4.5 98 150 26.5 2.6 330 2503

Fig. 2 Field location map (right) and schematics of fields boundaries (left)

Field Initial GOC (ft-ss) Initial OWCWOC (ft-ss) Initial Pressure at GOC (psi)

Tullich 5525 (North) & 5475 (South) 5735 2450

Gryphon 5541 5731 2510

Harding 5541 5804 2480

Maclure 5497 ( North Lobe) & 5541 (South Lobe) 5806 (South Lobe) 2503

Aberdeen

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Table 3 Summary of Rock and Fluid Properties

Oil recovery mechanism in the Gryphon area is dominated by strong aquifer drive and augmented by water injection in the

water leg. Fluid withdrawal from the oil column together with active aquifer influx and water injection has made the oil-water

contact risen both in formform of local water coning and increase of the water tablefree water level. Unfavourable mobility

ratio in the fields also makes the reservoir very prone to water coning. Well logs from recently drilled wells in Gryphon and

Harding exhibit an evidence of moving oil water contact which leaves some residual oil saturation behind. These findings

might be taken as the lowest actual saturation that could be achieved in the given reservoir condition. However some questions

arise whether the saturation will keep decreasing as the advancing oil-water contact moves further up-structure, as the water

might have not completely displaced the mobile oil fraction. The history matched simulation model from Gryphon shows that

water cusping occurred in horizontal producers and created local swept zones as shown on figure 2.

Literature Review

Review on Available Core Data

Coring operation were conducted using 8.5 in core bit mostly using oil-based / bland mud as drilling fluid with fiberglass

core sleeve. Since the reservoir section is highly unconsolidated, great care was taken to recover core with the minimum of

damage, and the core was frozen at the wellsite. A total number of 4000ft core sample was recovered from Gryphon, and the

other fields, followed by routine and special core analysis. The detailed procedures for routine and special core analysis

measurements are explained in Appendix 5..

Oil-water relative permeability analysis was conducted using unsteady state methods using both fresh state and cleaned

state plugs. The test was conducted in low rates in the range of 3 – 10 cc/min using refined mineral oil which viscosity is

modified to match the viscosity ratio in reservoir condition of 11:1. The experiments were done at ambient temperature and

elevated overburden pressure of 1500 and 2200 psi. Water flood susceptibility analysis (WFS) was conducted using both

cleaned state and fresh state plugs at reservoir condition using the same refined mineral oil used in the relative permeability

measeurement.

Wettability data was measured using AAmottMOTT and USBM method on fresh, cleaned, and restored plugs. The

observed wettability data shows that Balder Massive Sandstone comprises of mixed, intermediate, and neutral wet rock as

described in [Gryphon FDP [, 1992] and is shown on figure 3..

Fig. gure 1 Gryphon sSimulation mModel

Fig.ure 2 Fig. 3 Cross sSection of gGryphon sSimulation mModel sShowing mMovement in OWC in the forms of water cusping

around horizontal production wells and moving free water level at a larger scale.

Moving free water level

Water cusping


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5

Wettability Effect To Sor

0

10

20

30

40

50

60

0 0.2 0.4 0.6 0.8 1

Wettability Index to Water

So

r (%

)

Clean State

Fresh State

Restored State

Poly. (Fresh State)

eElectrical properties measurements including formation resistivity factor and formation resistivity index are conducted

under ambient temperature condition and overburden pressure up to reservoir pressure using cleaned state and fresh state

plugs.. Table 4 summarise the type of SCAL analysis with the corresponding number of samples.

Core water flood test results are available from 39 fresh and cleaned states samples from Gryphon and Maclure with

sample dimension of 1.5 inch diameter and 2-3 inch length

There are 280 conventional core plug samples that went through oil saturation analysis using Dean Stark extraction

method. The plugs are taken from the clean sandstones zones in the oil and water legs. The method uses extraction of oil under

reflux of alternating toluene and methanol as solvents. Dean Stark saturation data is used as a quality check of log-derived

saturation for both oil and water.

Table 4 Number of Samples Available from Various SCAL Analyses Core water flood test results are available from 39 fresh and cleaned states samples from Gryphon and Maclure with sample

dimension of 1.5 inch diameter and 2-3 inch length. The available data then compared to see the effect of the amount of pore

volume (PV) of water sweep to Sorw. Buckley Leverett analysis was conducted to all refined oil-water relative permeability

curves to present theoretical relation of Sorw to the amount of PV water injected which was not achieved during the water

flood test. The calculation details of Buckley Leverett method is presented in Appendix III

AnAnalysis No of Samples

Tullich Gryphon Harding Maclure

Unsteady State Kro-Krw 8 55 13 13

Water flood 0 33 6 0

Wettability 0 71 0 6

Electrical Properties 8 87 43 13

Table 4 Number of Samples Available from Various SCAL Analyses

Open-Hole Log Data Review

Open-hole log data sets from all fields are available from both original borehole and sidetracks. From which majority

(>80%) were drilled using oil-based mud and the remaining using water based mud. Discovery and appraisal wells were

logged by wireline and most of development wells by Logging While Drilling (LWD) tool. Early appraisal wells were logged

using wireline log with Sstandard set of triple combo which consists of gamma-ray; calliper, sonic, density, neutron, and

resistivity or induction tool with wireline conveyed were run in early appraisal wells. . Meanwhile typical LWD bottom hole

assembly consists of gamma ray, resisitiviy, neutron, and density tool.

Two wells that exhibit swept zones are found in Gryphon and Harding which are the pilot hole of 9/18b-A30 in

GryphonIntroduce the wells and 9/23b-29A in Harding. Both wells were logged using LWD tool which consists of gamma

ray, resisitiviy, neutron, and density tool. The A30 pilot hole is a development well and reached TD on 17 September 2007

with the objective of Balder Massive Sandstone. It was logged using LWD tool and found the moving oil water contact at

5602 ft TVDSS, rising 129 ft from the original OWC at 5731 ft TVDSS. The apparent swept zone is clean high porosity sands

Fig. 4 Reservoir wettability data measured from various type of core plugs. Fresh state plugs show a variety of wettability state

from strongly oil wet to weakly water wet


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6

with gamma ray reading around 20 GAPI. The average resistivity value over the swept zones is 0.6 ohm.m. The other well is

9/23b-A29 in Harding was drilled targeting the same Balder Massive Sandstone and found oil water contact at 5625 ft TVDSS

rising 179 ft from the original OWC at 5804 ft TVDSS.

Literature Review Sorw from Open Hole Log

The idea of determining Sorw from open hole log is to calculate saturation in a water-swept zone resulted from moving oil-

water contact. Wells are carefully selected for those which exhibit moving oil-water contact that is vertical wells or pilot holes.

These wells are expected to exhibit a clear contrast of saturation in the swept zones. Sorw calculation from open hole logs are

very sensitive to various element including the type of drilling mud, shale volume which resulted to porosity values, and a

number of electrical properties as constants in water saturation formequation. In order to produce a valid outcome, the result

from open hole logs is calibrated using core analysis data. Accurate calculation of water saturation from open hole logs in

swept zone is more difficult than in oil zone, as small amounts of measurement error have large effects at high Sw as found by

[Al-Sabea, [2004]. Accurate porosity, resistivity, and formformation water resistivity (Rw) is required, and also good

understanding of cementation factor exponent (m) and saturation exponent (n) for the respective formformation.

Sorw from Special Unsteady State Oil-water Relative Permeability Analysis Core Analysis

Unsteady state displacement method has been a preferred industrial standard for relative permeability measurement since it

is simpler and faster to be carried out as recommended by [Stiles, [2004]14

. And also the fact that In particular, imbibition

unsteady state methods physically mimics the displacement process in the reservoir whereas oil first saturates the reservoir and

followed by water as displacing fluids, and . And the fact that unsteady state method is conducted in a relatively higher rate

than steady state. In unsteady state method core are saturated with crude mineral oil up to initial water saturation (Swi) and

then brine is introduced. The measured oil and water rate are then taken for relative permeability using Johnson-Bossler-

Naumann (JBN) method as described by [Stiles [, 2004]. The test was carried out using unsteady state method by flooding

displacing refined mineral oil the plug with simulated formformation brine in constant flooding pressure at low rates using oil-

water viscosity ratio equal to 11:1.

Normally high viscosity mineral oil is used which leads to early breakthrough followed by two phase flow. The period of

two phase flow is controlled by the wetting state of the sample, at which strong oil wet condition will allow a longer period of

time as found by [Anderson [, 1987]. However, in a high oil-water viscosity ratio, the period of two phase flow is also

significant regardless the wetting state of the rock as observed by [Anderson [, 1987]. The possible weakness is the lack of oil

relative permeability data at high water saturation where the test is terminated which makes residual oil saturation may higher

than the actual value. Some authors [Cordiner, [1972],; Davies, [1993];, Hirasaki, [1996],; and Rathmell, [1973] 6, 7, 9, 13

suggest that centrifugation after unsteady state may define the extension of valid Kro curve from the high rate flood and to

diminish the capillary end effect. In a strongly water wet sample, most oil will be produced before the breakthrough with

minimum or zero oil production afterwards. When the test is conducted at favourable oil-water viscosity ratio, the plug will be

flushed down to irreducible water saturation at a short period of time as observed by [Anderson, [1987]. The opposite

phenomenon occurs in a strongly oil wet sample, when it takes a long period of two phase flow to flush the core down to

Swirr.

However, sSeveral considerations should be brought up into our attention before taking laboratory data for further analysis.

Inappropriate coring fluids, incorrect sample preservation, sample cleaning and drying, and use of refined oil might lead to

wettability alteration as shown by several authors [Anderson2, [1987]; Anderson

3, 1987; and Kennaird, [1988].

2, 3, 10. Result

should also be used in cautious way if the tests are conducted on individual short core plugs and at ambient conditions.

Conducting the test at low rates also potentially create capillary end effects especially in an intermediate wettability and high

permeability (>500 mD) samples [Stiles, 2004]14

. It is also often difficult to enforce a sufficient pressure differential across the

core in an unsteady state waterflood to reduce capillary forces without flood becoming unstable. This can be mitigated through

use of long composite core.

Refining the relative permeability curve is needed to extend the data beyond the saturation range achieved in the

laboratory. The value of Krw at Sor which is referred as Krw end point often used as an indication of the wettability of

rock/fluid system. Should the value of Sor be too high due to premature ending of the flood, the Krw end point will be too low.

These are undertaken by fitting the data into a curve generated from a power function of Corey exponent, and extend the curve

to the wider saturation range than one reported by the laboratory result.

Previous works by several authors [Davies, 1993; Kennaird, 1988; Rathmell, 1973] 7, 10, 13

shows that when the plug is

flooded at a higher rate with a higher terminal pressure differential, the flood would have proceeded to lower oil saturations.

Such a high rate is often referred as bump flood, and is conducted at the end of a conventional core floods experiment. The

work by Gauchet et.al, (1993) as cited by [Stiles, 2004]an author14 explains the decrease in the Sor values with an increase of

pressure differential of intermediate wettability sample. No effect was observed when the test was conducted on a strong

water-wet sample. And an increasing trend of Krw end-point was also observed with the increase of differential pressure

It is often reported that a test result from a single test might not present consistent data over the range of of saturations of

interest. And it is important to incorporate results from different test to define the entire relative permeability curve. The check

of Corey exponents should also be consistent with wettability measurement with the guidelines shown on the following table 5

which was cited from [Stiles, [2004].

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7

Wettability Corey Exponent Krw End Point

No Nw

Strongly Water-Wet 2 to 3 4 to 6 0.1 to o.4

Mixed Wettability 3 to 5 2 to 4 0.5 to 0.9

Oil Wet 6 to 8 1.5 to 3 0.8 to 1.0

(Re-printed from Stiles [2004])

End-point value approaching or exceeding 1.0 may be the result of wettability of the core has been altered to oil wet by

inappropriate coring fluid i.e. oil base mud. Sor values obtained from different test procedure might give different results with

water flood test being the most affected by capillary end effect. Calculated water relative permeabilities which are too high

early in a water flood are one of the most common problems associated with unsteady state test.

The Kro curve can then be extended in the same way of Krw. The final oil saturations reported at the end of core floods are

often significantly higher than the true residual oil saturation for the rock as observed by [Stiles [, 2004]14

. This is often due to

the pressure differential across the core being insufficient to overcome the capillary pressure at lower oil saturations.

Data Screening

As laboratory works for core analysis studies were carried out by different vendors, the consistency of results become

questionable when laboratory techniques are not standardised. In the case of existing data, a validity check should be

conducted and any discrepancies should be identified. It is necessary to identify valid test results and select for representative

data among the vast amount of available data. The proposed method by [dDos Santos [, 1997]8 is to check if the experiment

followexperiments follow several conditions which are:

- The capillary number associated to the displacement should be lower than 10-5

- The end effect must be negligible.

- The displacement must not show gravity segregation.

Capillary number (Nc) is a function of fluid viscosity, oil-water interfacial tension and displacement rate., in which inIn

the reservoir this number should be in the range of of 10-7

or less because of low velocities. However, in the laboratory

experiments this number is often much higher because the displacement rates are higher than in the reservoir. The capillary

number is related to the immobile oil droplets in the end of core sample at the end of displacement process. This oil saturation

will become mobile when the “drag” force of water is larger than the trapping capillary pressure. The residual oil saturation

will be at maximum when the capillary number is smaller than 10-5

and below that number the oil droplets will start to be

mobile due to the “drag” force.

As oil-water displacement is a resultant of viscous and capillary force, the dispersion of the flood fronts is controlled by

capillary forces. When it is reduced the dispersion of the flood front is negligible and water saturation will change sharply

before and after the front which is normally called “piston like displacement”. It is a necessary condition for the conventional

Johnson-Bossler-Naumann (JBN) method to be applicable for relative permeability calculation. Having the flood front

dispersed, the variation of residual saturation behind the front will be more gradual and does not reflect the true residual oil

saturation. This phenomenon is defined by end effect number (Nend) which is a function of the distance or the length of the

core plugs, oil viscosity, permeability, porosity and the displacement rates. In order to have a “piston like displacement” the

end effect number should be less than 0.1.

Another screening criterion is to find whether the test result is affected by gravity segregation during the test. This is to

ensure that the pressure drop over the core due to viscous force must be larger than the hydrostatic pressure of water and oil.

But given the small size of of core plugs, this condition is practically always met. This phenomenon is defined by gravity

number (Ng) which is the function of oil and water density, displacement rate, sample dimension, permeability, and oil

viscosity.

Core Water Flood Test.

Core water flood experiments has a similar procedure to oil-water relative permeability experiments where core is saturated

by mineral oil and then flushed by water as displacing fluid at a constant pressure. Bland mineral oil is used to match 11:1

viscosity ratio to brine and the iIncremental flow of oil and water volumes areflows of oil and water volumes are recorded as a

function of time. The displacement is carried out at a low rate of 5cc/sec until until the water cuts exceed 99.9%. The oil

saturation at this point might be referred as residual oil saturation, and to overcome the capillary end effect, a final flush at

higher rate of 500cc/sec was conducted and it is referred as bump flood. New residual oil saturation then again measured

which normally gives lower residual oil saturation values.

Table 5 Values of Corey Exponent for Different Types of Wettability







Formatted: Centered


8

Core water flood experiments has a similar procedure to oil-water relative permeability experiments where core is saturated

by mineral oil and then flushed by water as displacing fluid at a constant pressure. Bland mineral oil is used to match 11:1

viscosity ratio to brine and the incremental flow of oil and water volumes are recorded as a function of time. The displacement

is carried out at a low rate of 5cc/sec until until the water cuts exceed 99.9%. The oil saturation at this point might be referred

as residual oil saturation, and to overcome the capillary end effect, a final flush at higher rate of 500cc/sec was conducted and

it is referred as bump flood. New residual oil saturation then again measured which normally gives lower residual oil

saturation values.

A previous study by [Wood [, 1991] 18

shows that residual oil saturation in mixed wettability reservoirs by water flood is

often a strong function of pore volumes (PV) of water injected. Previous works by several authors [Cordiner [, 1972];, Davies,

[1993],; and Rathmell [, 1973]6, 7, 13

shows that in a high permeability sample, residual saturation that obtained from water

flood experiments do not represent the real residual saturation even bump flood has been carried out. The reason is for a high

permeability rock, a core flood only apply small pressure drop across the core, which leaves behind unswept region within the

core plugs.

Another work by [Hirasaki [, 1996] 9 reported that the Sorw of mixed wet sandstone system is sometimes very low, e.g =

10%. It can be measured only if the duration of the experiment is long enough and the driving force for displacement (gravity

or pressure gradient) is large compared to the capillary pressure retaining the oil as a wetting phase end effect. Welge’s

integration of Buckley Leverett equations could show that how many pore volumes of throughput will be required to reduce oil

saturation close to the Sorw.

Methodology

The exercise is to determine and integrate Sorw values is conducted by calculating the value from the existing water-oil

relative permeability data, open hole log data, and core flood data. Water-oil permeability data is refined to extend laboratory

measured value and then reliable sample are selected by using a screening criteria as described in detail in the following

section. Sorw from open hole log data is calculated using Archie formula over the swept zone, and the method will be

described also in the following section.

To seeinvestigate the extends effects of the amount of water injected to the true residual saturation, the refined water-oil

data was analyzed using Buckley Leveret method was used s to calculate fractional flow of water in vertical displacement from

core data. An attempt is to create use reservoir simulation as a tool was conducted by creating a sector model to find the

impact of the number of pore volume water injected to Sor particularly in the case of moving oil water contact. The sector

model is taken from Gryphon full field model particularly in the area penetrated by well 9/18B-A30 where moving contact was

observed from the open hole logs.

Data mining on open hole well logs, Routine Core Analysis (RCAL) and Special Core Analysis (SCAL) report was

conducted for all the fields. Open hole logs data are focused on vertical well and pilot hole which most likely intersect the oil-

water contact.

Another attempt to replicate the result of Buckley Leverett analysis on the log data was made tTo see the correlation

between oil saturation and the amount of water which has swept at a particular depth on a log data,. This was done by adding

together the bulk volume water (BVW) value in the bottom-up direction which acts as the water injection, and are plot it with

against the corresponding oil saturation (So). The obtained Sorw data then reconciled to produce a new range of applicable

Sorw.

The updated Sorw values arewere then implemented to the existing reservoir simulation model, by re scaling the existing

relative permeability curve, to look at the impact of different Sor to ultimate recovery. The available Gryphon simulation

model treats the entire field (Gryphon, Maclure, Tullich and Harding) as a single and connected geobody.

Relative Permeability Curve Refinement

All oil-water relative permeability curves generated from laboratory experiments were should be refined using the

workflow mentioned in previous section. The purpose is to obtain representative values of end point Sor, and also to generate

Corey exponents for each curve for Buckley Leverett analysis later on. The following steps were proposed by Stiles [2004] to

refine water-oil relative permeability data. First step of refining relative permeability curve is to observe the curve shape where

smooth and monotonic curves should be noticed for a good quality relative permeability data as shown on figure 4(a). This

followed by plotting the curve in log-log graph where good quality data should give concave downward for both oil and water

curve as shown on figure 4(b). Next is to estimate the value of Krw end point by normalising the water curve (Swn) and

plotting the Swn over Krw from on a log-log scale. Valid data will yield straight line if the flood is stabilize and extrapolation

to the Swn equal to 1 (Sor) will yield an estimate to Krw end point as shown on figure 4(c). The value of Corey exponent for

Krw curve (Nw) can be calculated using the following equation.

end-point

w

log log

log 1.0 log

rw rw

wn

K KN

S

… ……..................................................................................................................…... (1)




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9

Curve Refinement

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.0 0.2 0.4 0.6 0.8 1.0

Sw

Kr

Krw

Kro

`

Curve Refinement

0.00

0.01

0.10

1.00

0.0 0.2 0.4 0.6 0.8 1.0Sw

Kr

Krw

Kro

`

Krw End Point

y = 0.61x1.70

R2 = 0.99

0.100

1.000

0.1000 1.0000Swn Refined

Krw

Lab

510

uo

cN

110Lu

o

k

endN

The resulting values of Nw are then plotted against water saturation and the stabilized values of Nw is taken as the reliable

value, with the same way was used to determine No as shown on figure 4(e). The Krw curve then could be refined by the

following equation.

The next step of refinement is to estimate Sor value and extending the Kro curve, which is conducted by normalising the

oil saturation using different values of assumed Sor and plotting the result versus Kro on a log-log plot as shown on figure

4(d). The value which yields a straight line is used as an estimate of Sor with the slope being Corey exponent to oil (No). Kro

curve then could be generated using the following power equation.

Different values of Sor are substituted to the Son equation above and the results plotted versus Kro. The value of Sor which

yields a straight line is then used as Sor as shown on figure 4(d). The plot of relative permeability in a log-log scale is useful to

construct smooth Kro curve at low water saturations where little data are often available from the laboratory measurement.

Having refined all the end-points and Corey exponents, a new set of curve could be generated and it is shown on figure 4(f).

Data Screening

Screening of valid laboratory results for oil-water relative permeability is conducted by calculating capillary number, end

effect number, and gravity number for each sample. The three constraints are defined by the inequalities below, and the range

of values for each parameter are summarised in table 6 as cited from Bona [2000].

This screening method largely pointed out that in the common industrial practice of relative permeability

determination by unsteady state method, capillary forces are neglected. This is true when the core sample is long enough, but

in the reality core plugs usually does not exceed 15-20 cm (6-8 in). The three criteria mentioned above will provide a validity

check to the routine JBN (Johnson-Bossler-Naumann) method to calculate relative permeability at given displacement rate and

core sample lengths in the laboratory.

(Re-produced from Bona [2000])

Table 6 Range of Values for Screening Criteria Capillary Number (Nc) End-effect Number (Nend) Gravity Number (Ng)

Min 1.80E-06 5.30E-03 1.60E-06

Max 1.00E-05 1.00E-01 1.00E-02

…..………… (5) .………… (6) 210

Luo

gDk

gN

.……………… (7)

end-pointwN

rw rw wnK K S ……....................................................................................................................….........….. (2)

1

1

w oron

wi or

S SS

S S

……………...………....……….

(443)

1

1

oN

w orro

wi or

S SK

S S

……………………..................……

(334)


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10

Sro Determination

0.001

0.01

0.1

1

0.010.11Son

Kro

Sro 1

Sro2

Sro3

Corey End Points

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.00 0.20 0.40 0.60 0.80

Sw Refined

Nw

* an

d N

o*

Nw

No

Curve Refinement

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0

Sw

Kr

Krw

Kro

Krw, ref.

Kro, ref.`

Open Hole Logs Analysis

After doing data mining on all available well log curves, there are two wells only which exhibit moving OWC. One well is

found in Gryphon which is well 9/18B-A30 and another one is found in North Harding which is well 9/23B-A29. Sorw values

calculated from these wells will be the basis of log-derived Sorw.

Porosity Model

Previous study shows that Balder Massive Sandstones is a clean formformation with very low shale volumes that makes

standard neutron and density data is valid for porosity calculation. Porosity in clean sands can be expressed as:

wWhere in this case PHI = PHIT = PHIE and equation (8) will subsequently be used for porosity calculation.

Water Saturation Calculation

Archie formequation for clean sand is applicable to calculate water saturation over the net interval in Balder

FormFormation. Water saturation is then calculated using the formequation below:

Fig.ure 3 Fig. 5 Relative pPermeability cCurve rRefinement wWork fFlow as suggested by Stiles [2004] from raw data

(a) (b) (c)

(d) (e) (f)

fma

bma

PHI ….........................................................................................................…………………….…..…….…… (8)

n

t

w

mwR

RaS

1

………………………….…..........................................................................................................……… (9)

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11

Electrical properties measurements on core sample were conducted at in-situ stress and salinity conditions using fresh state

plugs to determine cementation factor “m” and saturation exponent “n”. FormFormation resistivity factor (FRF) which

measured at overburden pressure is plot against porosity on a log-log scale giving the gradient of cementation factor.

Resisitivity indexSaturation exponent was measured during waterflood test (imbibitions process) and was obtained by taking

the slope of FormFormation Resisitivity Index (FRI) with fractional water saturation plotted on a log-log scale. Histogram of

m and n then constructed. Water reisitivity (Rw) value are obtained from the histogram of apparent water resistivity value

(Rwa) calculated from deep resistivity (Rt) using the following formequation

Sensitivity in Archie Equation

Archie equation is error prone since some of the parameters are directly measured and others are indirectly derived. To

capture the uncertainties in each Archie constant, a method to calculate partial error contribution of each parameter to water

saturation is used as observed by Chen [1986]4. The method is based on standard analysis of error, and using the variance of

each parameter to calculate the fractional error contribution denoted as Cxi. The associated formequations for each Archie

parameter are:

Standard deviation (σxi) of each variable is calculated by assuming some uncertainties which normally attributed in each

measurement or experiment to derive each parameter. The assumed uncertainty (± yi%) can be used to provide the best

estimate4 of ± σxi by taking the base case value Xi as the multiplier, which is normally the mean value.

Results Open Hole Log Result Analysis

Porosity

Log derived porosity was found to be in a good agreement with core porosity measured at in situ stress condition. The

calculated average porosity is in the range of 30-36% over the net sand. The comparison of log derived porosity superimposed

with core porosity is shown on the figure 5 from well 9/18B-11 as an example in which core porosity data is available. The

core porosity shown as black dots are in good agreement with PHI curve.Gamma ray curve on the gamma ray track also show

very clean sand interval at 22-25 GAPI.

Water Saturation

Electrical properties and water resistivity data are presented in histograms and are shown in Appendix III. The mode values

of saturation exponent and cementation factor histograms are 2.70 and 1.71 with standard deviation of 2.71 and 1.74

respectively. The cementation factor indicates the typical value of slightly cemented sands, which might be not so accurate for

Balder Sandstone which is found to be much unconsolidated. The standard deviation values will be used as an input for

sensitivity analysis later on. Apparent water resistivity histogram has the mode value of 0.062 ohm.m and standard deviation

of 0.332 ohm.m. Direct measurement on several formformation water samples give an average water resistivity of 0.108

ohm.m at 77 deg F or equivalent to 0.0616 ohm.m at reservoir temperature. Table 7 summarise the statistical data from Archie

parameters calculation.

The graphical results of the calculated water saturation for both well 9/18B-A30 and 9/23B-A29 are presented on figure 7

6(a) and (b) respectively. Most likely value is shown by blue curve on water saturation track and denoted as P50 water

saturation. The uncertainties in Archie parameter are captured by calculating the P90 and P10 values as shown by red and

green curves respectively. In the clean sandstone body found in well 9/23B-A29 of Harding, the P50 Sor is found in the range

of 20-25% which is gradually decreasing over depth. The lowest Sor found to be at the lowest depth and increasing upwards.

On the other hand, similar trend was not found in well 9/18B-A30 of Gryphon where the P50 Sor is found in the wider range

of 10-27%. The tabulated values of log derived Sorw are presented in table 9.

mPHIRtRwa …....……………………...........................................................................................................…… (10)

2

mC …..…………….………....................… (14)

…..…………...……...................…… (15)

…..…………….........................…… (16)

2

2

ln

ln

nn

mm

SwC

C

iixi Xy % …....…....................................................................................................................................……… (17)

2

2

2

RtC

RwC

aC

RtRt

RwRw

aa

………............................................………… (11)

…………........................................……… (12)

…………….….....................................…… (13)

Formatted: para


Formatted: para

Formatted: para


12

Water-Oil Relative Permeability Sor Histogram

0

1

2

3

4

5

6

7

00.

020.

040.

060.

08 0.1

0.12

0.14

0.16

0.18 0.

20.

220.

240.

260.

28 0.3

0.32

0.34

0.36

0.38 0.

4

Sor

Fre

qu

en

cy

All SCAL Data

Water-Oil Relative Permeability Histogram

0

1

2

3

00.

020.

040.

060.

08 0.1

0.12

0.14

0.16

0.18 0.

20.

220.

240.

260.

28 0.3

0.32

0.34

0.36

0.38

Sor

Fre

qu

en

cy

Validated SCAL Data

Core Analysis Result

Oil-Water Relative Permeability

Residual oil saturation from refined oil-water relative permeability curves are tabulated as a histogram in figure 6 (a).The

values range from the lowest of 10% to 40% at the highest with mode of the data at 20%. After applying the screening criteria

using as explained in the previous section, the number of samples was highly reduced and a new histogram of Sorw is

constructed as shown on figure 6(b). Given the small number of samples that follows the criteria, the range of Sorw is also

narrowed from the lowest of 16% to the highest of 31%.


Dean Stark

Residual oil saturation from Dean Stark extraction method is presented as a histogram in Appendix 5. The histogram shows

that the Sor range from 5% to 98% with no obvious distribution is observed. The result becomes highly questionable as oil

saturation above 27% should have been mobile referring to the highest Sor from open hole log results. Core samples in which

Dean Stark analyses were conducted are taken from the oil zone which has not been flushed by moving oil water contact.

Therefore the oil saturation from Dean Stark becomes incomparable to the Sorw from oil-water displacement experiments in

SCAL. In this instance, only the lowest limit of residual oil saturation from Dean Stark method is taken as a reference which is

5 %.

Table 7 Archie Equation Parameters

Cementation

Factor (m) Saturation

Exponent (n) Apparent Water

Resistivity (Rwa)

Mode 1.71 2.70 0.062

Median 1.71 2.60 0.058

Average 2.19 2.58 0.072

P10 1.60 1.78 0.109

P50 1.71 2.60 0.040

P90 1.95 3.16 0.058

Std Deviation 1.74 2.71 0.332

Table 8 Uncertainties in Archie Parameters

m n Rwa Φ a Rt

Uncertainties (%) 5 5 5 10 0 5

Well Low Most Likely High Avg Φ

9/18B-A30 (Upper) 0.05 0.1 0.2 0.3

9/18B-A30 (Lower) 0.1 0.2 0.25 0.3

9/23B-A29 0.18 0.2 0.3 0.38

Table 9 Residual Saturation from Open Hole Log

Fig.ure 4 Fig. 6 Comparison of lLog and cCore pPorosity

Fig.ure 76 Sorw Histogram from Relative Permeability Analysis

(a) (b)




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13

Dean Stark Histogram

0

2

4

6

8

10

12

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Sor (%)

Fre

qu

en

cy

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%Frequency

Cumulative %

Well Low Most Likely High Avg Φ

9/18B-A30 (Upper) 0.05 0.1 0.2 0.3

9/18B-A30 (Lower) 0.1 0.2 0.25 0.3

9/23B-A29 0.18 0.2 0.3 0.38

Fig.ure 5 Fig. 8 Residual oOil sSaturation in oOpen hHole lLog (a) (b)

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14

Water-Oil Relative Permeability Sor Histogram

0

1

2

3

4

5

6

7

00.

020.

040.

060.

08 0.1

0.12

0.14

0.16

0.18 0.

20.

220.

240.

260.

28 0.3

0.32

0.34

0.36

0.38 0.

4

Sor

Fre

qu

en

cy

All SCAL Data

Water-Oil Relative Permeability Histogram

0

1

2

3

00.

020.

040.

060.

08 0.1

0.12

0.14

0.16

0.18 0.

20.

220.

240.

260.

28 0.3

0.32

0.34

0.36

0.38

Sor

Fre

qu

en

cy

Validated SCAL Data


Dean Stark

Residual oil saturation from Dean Stark Extraction method is presented as a histogram in Appendix 5. The histogram

shows that the Sor range from 5% to 98% with no obvious distribution is observed. The result becomes highly questionable as

oil saturation above 27% should have been mobile referring to the highest Sor from open hole log results. Core samples in

which Dean Stark analyses were conducted are taken from the oil zone which has not been flushed by moving oil water

contact. Therefore the oil saturation from Dean Stark becomes incomparable to the Sorw resulted from oil-water displacement

experiments in SCAL. In this instance, only the lowest limit of residual oil saturation from Dean Stark method is taken as a

reference which is 5 %.

Oil-Wwater Relative Permeability

Residual oil saturation from refined oil-water relative permeability curves are tabulated as a histogram in . The obtained

Sorw then presented on figure 68 (a). covering all available data.

TThe Sorw values range from the lowest of 10% to 40% at the highest with mode of the data at 20%. After applying the

screening criteria using as explained in the previous sectionthe three constants, the number of samples was highly reduced and

a new histogram of Sorw is constructed as shown on figure 8(b). Given the small number of samples that follows the criteria,

the range of Sorw is also narrowed from the lowest of 16% to the highest of 31% with no apparent trend observed.

Core Water Flood

Core water flood data are presented Residual oil saturation values from core water flood data are obtained when the

effluent of displacement has reached 99.9% watercut. The saturation in the core plug was calculated by taking the ratio of the

volume of oil produced to the initial oil in place. Oil saturation is plotted against the pore volume of water injected and the

final saturation is achieved at the end of the test. From the plot on figure 879(a) and (b) it is shown that oil saturation is a

function of pore volume water injectedas a plot of oil saturation as a function the amount of water injected in PV.

Figure 7 Dean Stark Oil Sor Histogram

(a) (b)



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15

Harding Core Flood

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30

Water Injected (PV)

So

(%

)

6E

13E

16E

42C

53C

47E

Gryphon Core Flood

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200

Water Injected (PV)

So

(%

)

13B 14A 11 1216 17 50 105106 108 109 143144 167 168 240V229VA 206VA 82V 87VA94VC 120VB 134VA 90VA162VA

(a) (b)

TThe plot on figure 879 shows that oil saturation decreases sharply showing that water breakthrough was achieved, and

subsequently two phases flow occur as more water is injected. Core floods data from Gryphon shows that oil saturation keeps

decreasing at approximately 140 PV of water injected. Most of the experiments were terminated when the oil volumecontent at

the core outlet is too low to be measured, although ever decreasing saturation is expected when the test is prolonged. Referring

to the wettability nature of Balder Sandstone which is indicated as a combination of intermediate, mixed, and neutral wet,

reduction in Sorw is expected in a prolonged test although the margin is not significant. Similar phenomenon is also observed

from Harding data which has similar porosity and permeability, but earlier termination of the test was observed after 20 PV of

water injected.

The residual oil saturation from core flood test ranges from 16% - 30% from Gryphon samples, and 10% - 30% from

Harding samples with one particular sample from Harding showing anomalously higher saturation of 40%., with anomalous

result then excluded from the majority of data. To see the extends of amount of water injected to the true residual saturation,

the refined water-oil data was analyzed using Buckley Leveret methods to calculate fractional flow of water in vertical

displacement. The calculated fractional flow then converted to oil saturation value and plotted over dimensionless water

injection in pore volume.

Buckley Leverett analysis shows that theoretical oil saturation will asymptotically reduced to residual saturation after being

swept by hundreds of pore volume of water. Figure 910 (a) shows the plot of theoretical oil saturation to the amount of pore

volume water injectedBuckley Leverett analysis from all relative permeability data set, and figure 910 (b) shows the result of

validated data set only. The replicated Buckley Leverett plot which is calculated from 9/23b-29A log data is superimposed

with relative permeability derived curve, and shown by the thick red line on figure 910 (b). The plot signifies a relationship

between log derived Sorw with the amount of PV water sweep, and current value of Sorw in the respective well is estimated to

be achieved after 30 PV of water swept.

,

and it indicates that the residual saturation obtained from core water flood test might be reduced to lower value when more

PV of water is injected.

An attempt to replicate the result of Buckley Leverett analysis on the log data was made to see the correlation between oil

saturation and the amount of water which has swept a particular depth. This was done by adding together the bulk volume

water (BVW) value in the bottom-up direction which act as the water injection, and plot it with the corresponding oil

saturation (So). This step was taken to the swept zone depth at which some amount of water has swept the oil as the oil-water

contact is rising. A well which shows clear swept zone over a clean interval, 9/23b-A29 was chosen to represent the modelling.

BVW is calculated by multiplying Sw and PHIE and added for each depth in PV unit.Taking the calculated value and

superimposed it with the same plot derived from the core Buckley Leverett analysis, the result shows similar trend and that

might indicate that oil saturation in this case Sor resulted from the vertical sweep is also a function of PV of water

encroachment.

16

Buckley Leverett Analysis

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0 20 40 60 80 100

Dimensionless Water Injected (PV)

Oil

Sat

ura

tio

n (

PV

)


0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0 100 200 300 400 500


Oil

Sa

tura

tio

n (

PV

)


0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0 10 20 30 40 50 60 70 80 90 100


Oil

Sa

tura

tio

n (

PV

)

Another attempt is to create a sector model to find the impact of the number of pore volume water injected to Sor

particularly in the case of moving oil water contact. The sector model is taken from Gryphon full field model particularly in

the area penetrated by well 9/18B-A30 where moving contact was observed from the open hole logs.

Sector model simulation also identifies the relation of Sorw to the amount of water sweep. (a)

(b)

Figure 101 shows vertical permeability values in each grid cell from the X slice where in that region which ranges from

500 to 1800 mD with no major flow barrier that allows the moving OWC sweeps the oil zonecolumn. Figure 112 shows the

development of moving OWC and the gradual changes in oil saturation as OWC is advancing. Eventually oil saturation does

not dropped to the lowest saturation which makes the oil phase become immobile, but it slowly decreasing as more volume of

water swept a particular depth.

Fig.ure 7 Fig. 9 Sorw Histogram fromLaboratory cCore water fFlood eExperiments results

(a)(b)

Figure 7 Laboratory Core Water Flood Test

Result

Fig.ure 8 Fig. 10 Buckley LLeverett aAnalysis on rRefined wWater-oOil rRelative pPermeability dData from (a) all available data and (b) validated data from screening criteria superimposed with replicated log-derived curve

(a) (ba

)

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17

Sor Reconciliation

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 1 2 3 4 5 6 7 8

Type of Test

Sor (Fract)

High Case Best Case Low Case

Implementation to Reservoir Simulation Model

Different ranges of residual oil saturation wereas obtained from different typesmeans of measurement, after previously

carefully selecting the available reliable data and refined it to produce a representative values. From every measurement, 3

values of Sor are generated giving the low case, best case, and high case estimate which the results are tabulated on figure 123.

Sor values from relative permeability end points, open hole logs from well 9/23B-A29, and core water flood analyses fall in

the range of 10%-30%, meanwhile open hole logs from lower layer of well 9/18B-A30, and Buckley Leverett analyses from

refined data has narrower range of 18%-25%. Open hole logs analysis from upper layer of well 9/18B-A30 resulted the range

of 5%-20%, and Dean Stark analysis only provides the low estimates of 5 % and the data is not very convincing due to the

wide spread of results. The final averaged low, best, and high case Sor are tabulated in table 10.

The updated Sorw values then implemented to existing reservoir simulation model to look at the impact of different Sor to

ultimate recovery. The available simulation model treats the entire field as one connected geobody where dynamics of oil and

gas production form one field is taken into account to the other fields. The new range of Sor was input to the history matched

water-oil relative permeability curves by changing the end-points to re-scale the curves. The existing data set relative

permeability curve used the in simulation model is shown on figure 143 and is where an equation was used to curve fit the data

to obtain a superimposed with the respective Corey model type equation. Having established the Corey exponent from original

curves, and the respective constants as shown in table 10. Figure 15 shows the new a re-scaled curves using the new range of

Sorw values is generated and presented in figure 143,. and itIt is obvious that lower Sorw end-point will drag the Kro curves

lower and vice versa. Thus the ultimate recovery is not only affected by the Sorw at the end of field life where oil phase

become immobile, but it also reducesd the overall relative permeability to oil from the beginning of production.

Cumulative oil production at 1 January 2018 is predicted from simulation model for each value of Sorw and the results are

summarised in table 11 and figure 15. The impact of different Sorw to the ultimate recovery to date is in the range of ±4% and

increasing to ±6% at 2018 which is considered on the low side.

Fig.ure 10 9 Fig. 11 Kv DistributiondDistributions in

sSector mModel

Fig. 12Sector model from Gryphon full field model showing decreasing oil saturation in the swept zones as oil water contact is increasing

Fig.ure 9 10 Sector mModel from Gryphon area full field model sShowing dDecreasing oOil

sSaturation in rRising oOil wWater cContact

No Type of Test

1 Dean Stark Data--

2 Relative Permeability End Point

3 Open Hole Logs 9/23B-29A

4 Open Hole Logs 9/18B-A30 Lower

5 Open Hole Logs 9/18B-A30 Upper

6 Buckley Leverett

7 Core Water Flood

No Type of Test

1 Dean Stark Data

2 Relative Permeability End Point

3 Open Hole Logs 9/23B-29A

4 Open Hole Logs 9/18B-A30 Lower

5 Open Hole Logs 9/18B-A30 Upper

6 Buckley Leverett

7 Core Water Flood

Fig.ure 12 Fig. 13 Sor Rreconciliation from different measurements


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18

Water-Oil

Relative Permeability Model

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Sw

Kr

Krw

Kro

Krw, ref.

Kro, ref.`

Fig.ure 11 Fig. 14 Relative Permeability Data and Curve-fitted Corey Model

Fig.ure 13 Fig. 15 Relative Permeability Model for Flow Simulation

Table 10 Relative Permeability End Points for Sensitivity Analysis

End Points Sor Kro Krw Nw No Swi

Existing Simulation Model 0.24 0.709 0.185 1.95 2 0.08

Base Case Sor Model 0.2 0.709 0.185 1.95 2 0.08

Low Case Sor Model 0.1 0.709 0.185 1.95 2 0.08

High Case Sor Model 0.3 0.709 0.185 1.95 2 0.08






Table 11 Ultimate Oil Recovery in Different Cases

Case Sorw % Change in EUR

Existing 0.24 0

Low 0.1 + 5.6%

Most Likely 0.2 + 1.4%

High 0.3 - 2.3%

Case Sorw Ultimate Recovery

Existing 0.24 213 MMSTB

Low 0.1 225 MMSTB

Most Likely 0.2 216 MMSTB

High 0.3 208 MMSTB

Water-Oil


0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

0.00 0.20 0.40 0.60 0.80 1.00

Sw

Kr

Krw, ref. Kro, ref. Krw Base Case Kro Base Case Krw Low Case Kro Low Case Krw High Case Kro High Case

Water-Oil


0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

0.00 0.20 0.40 0.60 0.80 1.00 Sw

Kr

Krw, ref. Kro, ref. Krw Base Case Kro Base Case Krw Low Case Kro Low Case Krw High Case Kro High Case


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19

Partial Error Contribution

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

0.00 0.10 0.20 0.30 0.40

Porosity [v/v]

Fra

ctio

na

l E

rro

r C

on

trib

uti

on

[%]

Rt

Rw

Phi

m

n

m*

n*

DDiscussion Open Hole Log

Different trends were observed in open hole logs result, where 70 ft of swept zone in well 9/23B-29A clearly shows lower

saturation at the lowest depth where more PV of water has swept the reservoir, and gradually increasing upwards. The clean

sands with uniformform porosity penetrated by the well have allowed a single observable trend. On the other hand, visible

swept zone in well 9/18B-A30 are separated by a shale break with approximately 30 ft clean sections above and below the

shale. Although similar porosity values are observed in both section but the calculated Sor are different. The upper section

shows lower residual oil saturation compared to the lower section although obviously less water has swept the upper section.

These differences raise a question regarding the development of residual saturation, which not only depends on the amount of

water swept but might also depends to other variables such as petrophysical properties of the rock itself.

As Archie equation contains six variables, it is become important to know which constant is sensitive to contribute errors

to the calculated water waturation. Using the proposed method which 4 described in methodology sectionpreviously described,

partial error contribution of each constant can be calculated for different values of porosity which, and the plot is shown on

figure 146. At low porosity formformation, the cementation factor and saturation exponent contribute errors up to 15% and

decreases for higher porosity. In the case of Balder Massive Sandstone with average porosity above 30%, none of the constant

contributes to the error of water saturation. This concludes that saturation measurement by open hole logs is reliable for the

given formformation. However, it is important to be noticed that this result only applies in homogeneous low resistivity zone

which in this case is the resistivity of swept zone. In both wells, the swept zone resistivity is around 0.5 ohm.m where the oil

zone the resistivity could be as high as 300 ohm.m.






Fig.ure 14 Fig. 16 Impact of dDifferent sSor to uUltimate oOil rRecovery

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20

Core Sor Relation to RQI

0

2

4

6

8

10

12

14

16

0 0.1 0.2 0.3 0.4 0.5

Sor (%)

RQ

I

Sor

Core Sor Relation to RQI

0

2

4

6

8

10

12

14

16

0 0.1 0.2 0.3 0.4 0.5

Sor (%)

RQ

I

Screened Data

Krw End Point Versus Permeability to Air

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1 2001 4001 6001 8001 10001 12001 14001

Ka (mD)

Krw

En

d-P

oin

t

Krw End Point

Corey Exponent to Oil Versus Permeability to Oil

0

1

2

3

4

5

6

7

8

9

1 1001 2001 3001 4001 5001 6001 7001 8001 9001

Ko (mD)

No

Krw End Point


0

10

20

30

40

50

60

0 0.2 0.4 0.6 0.8 1


So

r (%

)

Clean State

Fresh State

Restored State

Poly. (Fresh State)

Swirr Relation To Sor

0

10

20

30

40

50

60

0 10 20 30 40 50

Swirr (%)

So

r (%

)

Fresh State

Restored State

Clean State

(a) (b) (c)

(d) (e) (f)


0

10

20

30

40

50

60

0 0.2 0.4 0.6 0.8 1


So

r (%

)

Clean State

Fresh State

Restored State

Poly. (Fresh State)

(fe)

Core AnalysisCore Data

In order to find the dependency of residual oil saturation to other reservoir rock properties, several cross plot have been

created to find the trend of Sor with rock quality and different petrophysical properties. A constant called Reservoir Quality

Index (RQI) which is the square root of permeability devided by porosity is used to describe the trend of Sor to the rock

quality. On figure 17618 (a) and (b) all Sor data and screened data from relative permeability end points are plotted against

RQI, but the no obvious trend is observed due to very high permeability samples shows high Sor. This is somewhat different to

earlier findings that residual oil saturation and true residual oil saturation are dependent on the rock type due to differences in

pore geometry7 as investigated by Chang [1988]. This is could be caused by insufficient pressure differential across the core

during the laboratory displacement that could not displace oil at lower oil saturation after breakthrough.

The best value to measure true residual oil saturation is by conducting centrifuge capillary pressure measurement carried

out on preserved core material using degassed reservoir oil, and ideally should apply the reservoir confining pressure as

observed by Chang [1988] and Kennaird [1988]7, 13

. In the centrifuge test, sufficient pressure drop could be exerted even to the

small and high permeability plugs. Since centrifuge oil-water capillary pressure measurement is not available in this study, the

resulted laboratory displacement for both relative permeability and core water flood which were conducted in low rates are

potentially affected by capillary end effect. While the capillary effects are reduced in the centrifuge test, they are still present

and can be important at low oil saturation. It is therefore important to to correct calculated Kro values at low oil saturation for

Fig.ure 15 Fig. 17 Partial Error Contribution from Archie ConstantSensitivity aAnalysis of aArchie eEquation

Fig.ure 168 Fig. 18 Effect of pPetrophysical pProperties to SsSor and CcCorey eExponents


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21

the capillary end effects using result from the centrifuge capillary pressure measurement. Valid Kr curve should resemble

concave downward when plotted on log-log scale.

Unsteady state method has some drawbacks that could lead to inaccurate measurement of Sor. The early breakthrough

might be caused by water fingering since the mobility ratio of oil and water is high, which was attempted to be solved by low

rates displacement. However, low rates displacement will lead to severe end capillary end effect that holds much of the oil at

the end of the core sample since insufficient pressure differential is not achieved to mobilize oil. Another thing associated with

unsteady state method is there is no adequate capillary pressure to stabilise the flood front, which lead non-uniformfrom Sor

behind the flood front. This phenomenon will make average Sor across the core plug become inaccurate. To overcome

capillary end effect a higher rate displacement should be taken, and longer core sample should be used so that flood front

stability could be achieved using lower oil-water mobility ratio. Lower mobility ratio could also avoid early breakthrough and

water fingering.

The use of refined mineral oil also affected the quality of measurement since native wettability of the core has been altered.

Normally the mineral oil used for flushing does not alter the core wettability as they are non-polar and does not contain

surfactant as observed by [Kennaird et.al, [1988]. Many of the problems surrounding oil-water relative permeability are

associated with wettability. Much of the data are invalid as a result of the problem of wettability and capillary pressure.

Wettability is a subject of alteration as a result of inappropriate coring fluid, improper core preservation, incorrect core

handling, and unrepresentative test condition.To investigate the wettability effect to Sor, a cross plot of AMOTTAmott

wettability index to water and Sor was constructed and shown on figure 157 (fe). It appears that most of the data fall in the

both ends of wettability index, which are 0 and 1. The core sample becomes less water wet when the index goes to 0 and

becomes more water wet when it goes to 1. No specific trend observed from the wettability and Sor cross plot where all the

fresh state data tend to scatter. However, the plot shows that cleaned state plugs tend to become more water wet, which is the

case when the residual crude was successfully extracted from the plugs. Meanwhile restored state plugs tend to become more

oil wet as due to the ageing process.

Corey exponents to oil (No) from relative permeability data indicates that the samples taken for analysis are mostly strong

water wet following the criteria of wettability on table 5 where majority of the values are in the range 1 to 3. On the other

hand, Krw end points give a more moderate result where the values spread in the range of 0.1 to 0.7 which indicate mixture

between strongly water wet and mixed wet rocks. The tendency of being more water wet rocks explains that the observed Sor

values are on the high side, since previous author indicates that the Sor reached a minimum value when the core sample

exhibited neutral mixed wet as investigated by [Conti, [2004]5. Neutral wettability is defined as a wettability state which is

neither water-wet nor oil-wet. To minimize the uncertainty in predicting effective residual saturation in mixed wettability

reservoirs it is necessary to consider competing effect of relative permeability, gravity forces, and imbibition capillary pressure

In core water floods experiments, a strongly water rocks are characterized by small or zero production after breakthrough,

where the residual oil in strongly water wet rocks reside as discrete, discontinuous droplets surrounded by water as concluded

by 6 [Rathmell [1973]]. While the residual oil in strongly oil wet is continuous phase occupying the pore surfaces. For the

reservoirs considered in this study, no difference in residual oil saturation was observed between the fresh and the restored

state waterfloods. The decreasing oil saturation as a function of PV of water swept which observed in the simulation result

aligned with a previous work by [Anderson] [1987] which shows that Sor is related to the throughput for mixed-wet cores. In

mixed wettability systems, the relative permeability curves allow significant oil production after water breakthrough, with oil

draining from pores as a continuous wetting phase. A cross plot between Sor and irreducible water saturation (Swirr) generally

shows that Sor decreases as Swirr increases. In a water wet rock, water act as a continuous phase which attached to the rock

surface which makes Swirr becomes high, and similarly in oil wet rock.

Summary and conclusions

Unsteady state relative permeability data potentially affected by end effect and capillary effect

ROS in Gryphon Area is a function of PV water swept due to the intermediate and mixed wettability state of the rock

The recommended ROS in Gryphon Area is 10%, 20% and 30% for low, most likely and high case.

True oil saturation is the minimum oil saturation that can be achieved under the combined viscous, capillary, and

gravitational forces.

Unsteady state method mimics the displacement in reservoir condition in which oil as a displaced fluid and water as

displacing fluid with single phase oil flow followed by two phase flow.

Residual oil saturation from water oil relative permeability test should be refined to extend the Kro curve which could

not be achieved during laboratory test.

Laboratory data should be investigated to exclude unreliable result and

The high apparent residual oil saturations at low flooding rates due to capillary effects are an example of an invalid

result. Such invalid data are to be disregarded and not included in the reconciliation process.

For a typical water-wet or mixed wet type rock, the an accurate residual oil saturation measurement could be achived

is defined by the oil-water imbibition capillary pressure curveexperiment. However this method is not applicable for Balder

Massive Sandstone due to unconsolidated nature of the formation.






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22

(m)diameter Sample :

)(m/sconstant Gravity :

)(kg/m differencedensity oil water :

(m)length Sample : L

(%)Porosity :

)m / (mDty Permeabili :

(N/m) tension linterfacia oil- Water:

(m/sec)ity arcy velocD' :u

(Pa.s) viscosityOil :

2

3

2

D

g

k

(ohm.m)ty Resisitivi Water : Rw

(ohm.m)y resistivit True :Rt

(%) saturation Water : Sw

exponent Saturation :n

factorn Cementatio : m

factor Tortuosity : a

xiofon contributierror Fractional : C

valuecase Base : X

(%)y uncertaint Assumed :y

xi veriableofdeviation Standard :

xi

i

i

xi

number Capillary : Nc

(ohm.m)ty Resisitivi Water : Rw

(ohm.m)y resistivit True :Rt

(gr/cc)density Fluid: f

(gr/cc)density Bulk : b

(gr/cc)density matrix : ma

(%) volumeShale :Vsh

(%)porosity Total : PHIT

(%)porosity Effective : PHIE

(ohm.m)y resistivitater Apparent w : Rwa

oil ty topermeabili Relative : Kro

numberGravity : Ng

number effect End : Nend

(%) water tosaturation oil Residual : Sorw

(%) saturation water Initial : Swi

waterty topermeabili Relative : Krw

wateroexponent tCorey : Nw

oil oexponent tCorey : No

saturation oil Normalised :Son

Residual oil saturation could also be calculated from resisitivity data from swept zones. However an accurate

estimation of Archie constant is important as saturation calculation in swept zone is very sensitive.The sensitivity analysis

shows that the Archie equation is robust at the condition of the swept zone. An accurate true resistivity value could be

obtained from induction log which is accurate at low resistivity.

In Balder Massive Sandstone, residual oil saturation is a function of pore volume of water sweep shown by core water

flood data and reservoir simulation. In this case the further advancing of oil water contact will lead to lower Sor.

The average residual oil saturation for grater Gryphon Area is 10%, 20%, and 30% for low case, most likely case, and

high case respectively.

The change in Sor will re-scale the oil-water relative permeability data set, which at the end effecting the field

production profile.

Wettability in Balder Massive Sandstone are varies from strong oil wet to mixed wet which observed from AMMOTT

wettability data and Corey exponent values.

For high porosity reservoir, none of the Archie parameter becomes dominant as a source of error in water saturation

calculation.

The new range of ROS will change the ultimate recovery from -2% to +6%

Recommendations

The recommended practice is to conduct centrifuge at the end of flood experiments, since centrifuge could exert sufficient

pressure drop across the core. It is reported that residual oil saturation measured from centrifuge tests are lower than those

determined by coreflood tests. And it is essential to take residual oil saturation from oil-water imbibitionwaterflood capillary

pressure measurement to define oil saturation end points beyond the corefloods.

Results form flooding involving flushing with large number of pore volumes of water which do not use water saturated gas

can result in artificially low residual saturation due to stripping of light ends. First step in the use of oil-water displacement

data is to gain understanding of the history of the core material used in the test, the type of test conducted, and the laboratory

procedure and conditioned used. The inaccuracies associated with flooding small core plugs and to problem associated with

capillary effects require laboratory results to be refined before being used further.It also recommended taking core sample in

the swept zone and measuring the saturation to get the actual Sorw at reservoir condition.

Check of consistency from the data integration can be conducted by observing Sor values which should be decreasing from

reservoir condition waterflood, centrifuge kro, and centrifuge Pc respectively. The Sor resulted then decreases in for centrifuge

Kro test and centrifuge Pc test respectively.

Although much affected by capillary end effects, true residual saturation might be achieved from laboratory water flood at

favourable oil-water viscosity ratio. An example case is in a low permeability, strongly water wet rocks that is water flooded

using low viscosity oil and with numerous pore volume throughput. Data from long, composite core are more reliable in doing

this as capillary pressure effect is reduced.

Acknowledgements I wish to express my gratitude to Maersk Oil North Sea UK Limited for the opportunity to carry out my MSc thesis. Most

appreciation goes for my supervisor Fabrizio Conti and Stephen Milner, everybody in Petroleum Engineering Department

particularly in Reservoir Operation Group. Special appreciation is dedicated for Gabriel Marcas and Ritesh Kumar from

Mature Field Studies team for insightful discussion and assistance with Eclipse software. I would also like to thank my

supervisor and colleagues at Imperial College for the support and enjoyable time during the MSc study.

Nomenclatures


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References

1. Al-Sabea, Salem, Bean, Clarke & Crowe, John. (2004) Residual Oil Saturation Analysis of The Burgan FormFromation in

the Greater Burgan Field, Kuwait. Abu Dhabi International Conference and Exhibition. Abu Dhabi, United Arab Emirates,

Society of Petroleum Engineers.

2. Anderson, W. G. (1987) Wettability Literature Survey-Part 6: The Effects of Wettability on Waterflooding. SPE Journal of

Petroleum Technology, 39 (12), 1605-1622.

3. Anderson, William G. (1987) Wettability Literature Survey Part 5: The Effects of Wettability on Relative Permeability.

SPE Journal of Petroleum Technology, 39 (11), 1453-1468.

4. Anderson, William G. (1986) Wettability Literature Survey-Part 3: The Effects of Wettability on the Electrical Properties

of Porous Media. SPE Journal of Petroleum Technology, 38 (12), 1371-1378.

3.5. Chang, M. M., Maerefat, N. L., Tomutsa, L. & Honarpour, M. M. (1988) Evaluation and Comparison of Residual Oil

Saturation Determination Techniques. SPE Fromation Evaluation, 3 (1), 251-262.

4.6. Chen, H. C. & Fang, J. H. (1986) Sensitivity Analysis of The Parameters In Archie''s Water Saturation Equation.

(LOGANAL).

5.7. Conti, F. & Bona, N. (2004) EVALUATION OF RESIDUAL OIL SATURATION IN THE BALMORAL FIELD

(UKCS). SPWLA 45th Annual Logging Symposium. , Society of Petrophysicists & Well Log Analysts.

6.8. Cordiner, F. S., Gordon, D. T. & Jargon, J. R. (1972) Determination of Residual Oil Saturation AfterAfter

Waterflooding. SPE Improved Oil Recovery Symposium. Tulsa, Oklahoma, 1972 Copyright 1972 American Institute of

Mining, Metallurgical, and Petroleum Engineers, Inc.

7.9. Davies, G. W., Gamble, I. J. A. & Heaviside, John. (1993) Field-Wide Variations in Residual Oil Saturation in a North

Sea Sandstone Reservoir. SPE Advanced Technology Series, 1 (1), 180-187.

8.10. dos Santos, Renato L. A., Bedrikovetsky, P. & Holleben, Carlos R. (1997) Optimal Design and Planning for Laboratory

Corefloods. Latin American and Caribbean Petroleum Engineering Conference. Rio de Janeiro, Brazil, 1997 Copyright

1997, Society of Petroleum Engineers, Inc.

9.11. Hirasaki, G. J. (1996) Dependence of Waterflood Remaining Oil Saturation on Relative Permeability, Capillary

Pressure, and Reservoir Parameters in Mixed-Wet Turbidite Sands. SPE Reservoir Engineering, 11 (2), 87-92.

10.12. Kennaird, T. (1988) Residual Oil Saturations Determined by Core Analysis. Offshore South East Asia Show.

Singapore, 1988. Society of Petroleum Engineers Inc.

11.13. Purvis, K., Kao, J., Flanagan K., Henderson, J. & Duranti, D.(2002) Complex Reservoir Geometries in a Deepwater

Classic Sequence, Gryphon Field, UKCS: Injection Structures, Geological Modelling, and Reservoir Simulation. Journal of

Marine and Petroleum Geology. Elsevier Science.

12.14. Newman, M. St. J, M. L. Reeder, A. H. W. Woodruff, and I. R. Hatton. (1993) The Geology of the Gryphon Oil Field.

Petroleum Geology of west Europe: Proceedings of the 4th

Conference. The Geological Society, London, pp 123-133.

13.15. Rathmell, J. J., Braun, P. H. & Perkins, T. K. (1973) Reservoir Waterflood Residual Oil Saturation from Laboratory

Tests. SPE Journal of Petroleum Technology, 25 (2), 175-185.

14.16. Stiles, J. (20041995) Relative Permeability: It’s Use and Misuse in Reservoir Engineering. ENI In-house training.

Milan, Section 5, p 7-11.

15.17. Strange, L. K. & Baldwin, W. F. (1972) Core and Log Determination of Residual Oil After Waterflooding - Two Case

Histories. SPE Improved Oil Recovery Symposium. Tulsa, Oklahoma, 1972 Copyright 1972 American Institute of Mining,

Metallurgical, and Petroleum Engineers, Inc.

16.18. Syed, E. U., Salaita, G. N. & McCaffery, F. G. (1991) Determination of Residual Oil Saturation From Time-Lapse

Pulsed Neutron Capture Logs in a Large Sandstone Reservoir. Middle East Oil Show. Bahrain, 1991.

17.19. Valenti, Nick P., Valenti, R. M. & Koederitz, L. F. (2002) A Unified Theory on Residual Oil Saturation and Irreducible

Water Saturation. SPE Annual Technical Conference and Exhibition. San Antonio, Texas, 2002,. Society of Petroleum

Engineers Inc.

18.20. Wood, A. R., Wilcox, T. C., MacDonald, D. G., Flynn, J. J. & Angert, P. F. (1991) Determining Effective Residual Oil

Saturation for Mixed Wettability Reservoirs: Endicott Field, Alaska. SPE Annual Technical Conference and Exhibition.

Dallas, Texas, 1991 Copyright 1991, Society of Petroleum Engineers, Inc.

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APPENDIX – 1: Critical Literature Review1: Critical Literature Review 1

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APPENDIX 1: APPENDIX - 1 Critical Literature Review

SPE

Paper No

Year Title Authors Contribution

88628718

2

200419

77

Residual Oil

Saturation Analysis of

The Burgan Fromation in

the Greater Burgan Field,

Kuwait.HOW SHOULD

WE MEASURE

RESIDUAL-OIL

SATURATION?

Al-Sabea,

Salem, Bean,

Clarke & Crowe,

John R. E. Wyman

This paper gives an example of

integrated residual oil saturation with the

case study of Greater Burgan Field in

Kuwait. The paper describe how historical

Pulse Neutron Capture log data could be

used to monitor the decreasing residual oil

saturation over time and the possibility of

variation in residual saturation in spatial

point of view.

One of the very first paper that

comprehensively describe and compare

various methods of measuring residual oil

saturation, by open hole log, cased hole log,

core analysis, tracer test, and reservoir

performance

3791 1972 Determination of

Residual Oil Saturation

After Water flooding

F. S. Cordiner,

D. T. Gordon and J.

R. Jargon,

Members AIME,

Marathon Oil Co

The very first paper that includes

pressure transient test as a tool to measure

residual oil saturation. Pressure transient test

tells the in-situ parameter such as effective

permeability and total compressibility. Later

on compressibility value indicates that gas

saturation remaining after waterflooding is

essentially zero

14887 1988 Evaluation and

Comparison of Residual

Oil Saturation

Determination

Techniques

Chang,M.M.;

Maerefat,N.L.;

Tomutsa,L.;

Honarpour,M.M.

This paper compares the various method

for residual oil saturation (ROS) for both

single well measurement and inter-well

measurement. It also presents a screening

criteria to select the best method under

certain wellbore and reservoir conditions

and present the results in statistical approach

19851 1993 Field Wide Variations

in Residual Oil Saturation

in a Sea Sandstone

Reservoir

Davies,G.W.;

Gamble,I.J.A.;

Heaviside,John

The paper explain the work of extensive

coreflood analysis from Sea sandstone

reservoir to provide reservoir wide

description.Various factors are investigated

using more than 200 samples. It is also

explains ROS distribution in spatial

perspective

30763 1996 Dependence of

Waterflood Remaining

Oil Saturation on Relative

Permeability,

Capillary Pressure, and

Reservoir Parameters in

Mixed Wet Turbidite

Sands

G. J. Hirasaki Describe the dependencies of residual oil

saturation (ROS) on relative permeability,

capillary pressure, and reservoir parameters.

The author work with a core sampe of

Turbidite sandstone reservoir. It focus on

swept region after waterflooding in water

wet and mixed wet system.

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2

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16471123

923

198720

09

Wettability Literature

Survey-Part 6: The

Effects of Wettability on

Waterflooding Harding

Central—Achieving 74%

Recovery

Anderson, W.

G. P. Zhang and S.

Green

The paper is a comprehensive literature

survey on the effect of wettability to

waterflooding. The author compiled and

reviewed various core water flood

experiments and observes the impact of

changing wettability to waterflood

behaviour. Different wettability state

including water wet, oil wet and mixed wet

are discussed and compared to make clear

understanding on how different wetting state

could affect oil recovery.

The paper presents the success story of

Harding field reservoir management to

achieve high recovery factor

SPWLA

1986-

vXXVIIn5a3

1986 Sensitivity Analysis of

The Parameters In

Archie''s Water Saturation

Equation

Chen, H. C. &

Fang, J. H.

The paper provide a full sensitivity analysis

of the Archie water saturation equation,

assuming all six variables in the equatuion

to be error prone. The analysis was

performed in two models, (1) Equal

uncertainty and (2) unequal uncertainty. The

method proposed in the paper enables us to

quantify the error contribution of each

parameter. Sensitivity analysis become

important when the measurement of each

Archie parameter are not always accurate

and highly depends on the measurement and

interpretation technique.

SPWLA

2004-UUU

2004 EVALUATION OF

RESIDUAL OIL

SATURATION IN THE

BALMORAL FIELD

(UKCS)

Conti, F. &

Bona, N.

The paper provide of a case study for

residual oil calculation in Balmoral Field in

the UK North Sea using integrated core and

log analysis in the swept zone. The author

shows that not all the laboratory analysis

result is valid to be taken as a reference for

Sor study due to the associated uncertainty

from laboratory procedure and sample

condition.

39038 1997 Optimal Design and

Planning for Laboratory

Corefloods.

dos Santos,

Renato L. A.,

Bedrikovetsky, P.

& Holleben, Carlos

R.

The paper provides a method to quantify

different effect from laboratory experiments

in core water flood study. The method

proposed by the paper could be used for

planning a core water flood test to get a

reliable result.

17686 1988 Residual Oil

Saturations Determined

by Core Analysis

Kennaird, T. The paper discussed the result of

laboratory oil displacement experiments

using water and gas which conducted for

different purposes such as flood analysis

and relative permeability measurement for

various lithologies. The experiments were

conducted in different conditions such as

steady state, unsteady state, and centrifuge

at both reservoir and ambient temperature.




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3785 1973 Reservoir Waterflood


from Laboratory Tests

Rathmell, J. J.,

Braun, P. H. &

Perkins, T. K.

The paper presents the results of

theoretical and experimental study of

laboratory waterflood and core saturation

data which was obtained using water based

mud. The paper used previously published

information and its own experimental result.

3786 1972 Core and Log

Determination of

Residual Oil After

Waterflooding - Two

Case Histories.

Strange, L. K.

& Baldwin, W. F.

This is a case study of two fields under

waterflood which is assessed for tertiary

recovery. The method of determining

residual oil saturation comes from core and

log analysis. The paper investigate the effect

of mobile oil and water which lead to

flushing during coring operation which lead

the measurement become invalid.

3795 1991 Determination of


From Time-Lapse Pulsed

Neutron Capture Logs in

a Large Sandstone

Reservoir.

Syed, E. U.,

Salaita, G. N. &

McCaffery, F. G.

The paper shows the utilization of

Pulsed Neutron Logs to investigate the

relation of residual oil saturation to the

amount of water sweep in the reservoir. The

in situ measurement provides a reliable

result since it is free from potential error

during the laboratory experiments.

77545 2002 A Unified Theory on


and Irreducible Water

Saturation.

Valenti, Nick

P., Valenti, R. M.

& Koederitz, L. F.

The paper pointed out several classic

assumptions used in approximating

reservoir recovery in a small reservoir

which is no longer applicable when is used

in bigger reservoir. The unified theory of

residual saturation provides a general

approach for different type of reservoirs.

22903-

MS

1991 Determining Effective


for Mixed Wettability

Reservoirs: Endicott

Field, Alaska.

Wood, A. R.,

Wilcox, T. C.,

MacDonald, D. G.,

Flynn, J. J. &

Angert, P. F.

The paper explains the significance of

mixed wettability to effective water

saturation, in which the value is a function

of the amount of PV of water injected.


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A1.1 SPE 3791 - DETERMINATION OF RESIDUAL OIL SATURATION AFTER WATER FLOODING

Authors : F. S. Cordiner, D. T. Gordon and J. R. Jargon, Members AIME, Marathon Oil Co

Contribution:

The first paper that includes pressure transient test as a tool to measure residual oil saturation.

Pressure transient test tells the in-situ parameter such as effective permeability and total

compressibility. Later on compressibility value indicates that gas saturation remaining after

waterflooding is essentially zero

Objective of Paper:

This paper illustrates the use of several independent testing and calculational procedures for

determining residual hydrocarbon saturations remaining in a reservoir after waterflooding. These

methods consist of material balance calculations, analysis of well test data, pressure transient

testing, core analyses, and borehole log calculations.

Methodology used:

Test case was carried out using data from two Pennsylvanian and Devonian age sandstone

reservoirs in Illinois, USA. Both fields undergone 5 spot-10 acre spacing waterflood. Core data,

well log data and reservoir performance data as well as pressure transient test data were utilized

to calculate ROS in different methods

Conclusion reached:

Good agreement was obtained for values of water saturation after waterfloods from several

independent methods. Relative permeability data are important to analysis technique, where

laboratory derived kr should be carefully validated. Field case show that waterflood performance

tends to verify laboratory Kr as well as indicates values of Sor. A comprehensive approach using

all tools available resulted in satisfactory answer

Comments:

Although good agreement was achieved but this paper does not describe uncertainties in each

measurement which eventually should be included to reflect tools limitation.


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A1.2 SPE 14887 - EVALUATION AND COMPARISON OF RESIDUAL OIL SATURATION

DETERMINATION TECHNIQUES

Authors: Chang,M.M.; Maerefat,N.L.; Tomutsa,L.; Honarpour,M.M.

Contribution:

This paper compares the various method for residual oil saturation (ROS) for both single well

measurement and inter-well measurement. It also presents a screening criteria to select the best

method under certain wellbore and reservoir conditions and present the results in statistical

approach

Objective of Paper:

A brief review of available ROS tachnique is presented indicating advantages, limitations,

problems, and possible improvement of each techniques. Advantages and disadvantages are

summarized, and screening criteria to select the best method is presented. The paper also

presents ROS vertical profiles to eliminate ROS variations resulting from formation depths. The

vertical profiles based on ROS zoning and foot-by-foot measurements were studied to provide

more "resolution" for comparisons. The results show that discrepancies in measurement methods

are more pronounced when vertical profiles are divided into different zones. This could mean

that the discrepancies are much greater for some zones than for others. This approach offers the

possibility of studying ROS-method discrepancies as a function of different ROS values.

Methodology used:

The paper compares data from 89 measurements in 57 sandstones reservoirs and 18

measurement in 4 carbonates reservoirs from Interstate Oil Compact Comission (IOCC) in

Oklahoma using core analysis data, open hole, cased hole, tracer, and production data for

material balance.

Conclusion reached:

Each ROS technique offer advantages and limitations. The selection of effective technique

should be based on the formation and wellbore condition. Although some methods has been

improved, further improvement are still needed such as interpretation models, determination of

saturation exponents, and development of inter-well measurement.Resistivity logs tends to give

higher values and coring tends to give lower than average values. ROS zoning and foot-by-foot

comparison between the ROS vertical profiles provide better resolution for ROS comparison.

The comparison offer possibility of studying ROS method discrepancies as a function of depth.

Comments:

The paper gives an objective comment on how each method has its own disadvantages and

includes the uncertainty in measurement and how proper method should be select for different

reservoirconditions.








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A1.3 SPE 30763 - DEPENDENCE OF WATERFLOOD REMAINING OIL SATURATION ON RELATIVE

PERMEABILITY, CAPILLARY PRESSURE, AND RESERVOIR PARAMETERS IN MIXED WET

TURBIDITE SANDS

Authors: G. J. Hirasaki

Contribution Describe the dependencies of residual oil saturation (ROS) on relative

permeability, capillary pressure, and reservoir parameters. The author work with a core sampe of

Turbidite sandstone reservoir. It focus on swept region after waterflooding in water wet and

mixed wet system.

Objective of Paper:

The oil remaining after waterflood operations is sometimes divided into mobile, unswept oil

and immobile, “residual oil saturation” in the swept region. Here the paper will focus only on the

swept region. it will show that the much of the ROS in the swept region may be mobile. The

residual oil saturation, Sor, is defined here as the saturation at which the oil relative permeability

goes to zero. We show that the ROS in the swept region can be very different from S in mixed-

wet systems.

Methodology used:

The author uses finite difference grid reservoir simulation to simulate Buckley-Leverett

displacement process using water-wet and mixed wet core samples.

Conclusion reached:

"A mixed-wet sand may have a low residual oil saturation, Sor. This is a necessary but not

sufficient condition for a low ROS. Other conditions that need to be satisfied for a low ROS are

that (1) the dimensionless time for gravity drainage must be large enough, (2) the sand thickness

should be large compared with the capillary transition zone, and (3) either the mobility ratio be

small or the gravity number be significant compared with unity. In addition, the ROS’s of mixed-

wet systems are sensitive to the shape of the oil relative permeability curve (Corey exponent) and

the mobility ratio. "

Comments:

The paper show the example of using reservoir simulation to calculate ROS using calibrated

core data in mixed we turbidite reservoir which is the part of thesis project workflow.






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A1.4 SPE 19851 - FIELD WIDE VARIATIONS IN RESIDUAL OIL SATURATION IN A SEA SANDSTONE

RESERVOIR

Authors: Davies,G.W.; Gamble,I.J.A.; Heaviside,John

Contribution:

The paper explains the work of extensive coreflood analysis from North Sea sandstone

reservoir to provide reservoir wide description.Various factors are investigated using more than

200 samples. It is also explains ROS distribution in spatial perspective

Objective of Paper:

An extensive set of core waterflood data is analyzed to provide a reservoir-wide description of

residual oil saturation, provide a reservoir-wide description of residual oil saturation, Sor. Such

core tests are influenced by many parameters, including rock structure, wettability, fluid

properties, and experimental procedures. With a data set as large as that used here (more than

procedures. With a data set as large as that used here (more than 200 waterfloods) the effects of

these factors can be separated. It investigated rock structure, permeability, porosity, initial water

saturation, Swi, and wettability. The data indicated that variations in Sor were caused by trends

in Swi and wettability, both of which varied with depth across the transition zone. This implies

that a unique Soi/Sor relationship for this reservoir does not exist. The work presented here was

used to rescale relative permeability data in regions of the field where spatial variation in Swi

exists. The value of the large database for defining trends in reservoir behavior was significant

and enabled more accurate reservoir simulation. Introduction Reservoir performance evaluation

requires accurate description of the displacement processes.

Methodology used:

The paper draws on data produced from many core studies performed over period of time.

The author examines numbers of factors including wettability, flooding method, field procedure,

and laboratory procedures.

Conclusion reached:

Although the lithology of North Sea core is relatively homogeneous, but trends in waterflood

behaviour as a function of height above OWC were observed.Systemic procedures should always

be applied in SCAL analysis so that representative data can be obtained. The particular trend

observed show properties varying with height in the transition zone. Specific differences were

observed in ROS characteristics between samples from oil zone and transition zones.

Comments:

The paper specifically describes ROS characteristics from North Sea sandstone reservoir

generated from various methods and will be a good basis for my upcoming research project.







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8

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A1.5 SPE 88628 RESIDUAL OIL SATURATION ANALYSIS OF THE BURGAN FROMATION IN THE

GREATER BURGAN FIELD, KUWAIT.

Authors: Al-Sabea, Salem, Bean, Clarke & Crowe, John

Contribution:

This paper gives an example of integrated residual oil saturation with the case study of

Greater Burgan Field in Kuwait. The paper describe how historical Pulse Neutron Capture log

data could be used to monitor the decreasing residual oil saturation over time and the possibility

of variation in residual saturation in spatial point of view.

Objective of Paper:

This paper is a continuation of some previous study conducted in Greater Burgan reservoir.

Previously, the determinations of residual oil saturation only looks at one type of data at a time

and frequently give different answers. The aim of the current study is to integrate different type

of measurements to produce consistent result.

Methodology used:

Time-lapsed PNC log data from 22 years of field production has been used to monitor flood

front and the remaining oil saturation in the swept zones. This data is then compared to open

hole logs data from newly drilled wells that penetrated the swept zones. Core analysis data from

Dean Stark measurement and core flood test also being used. SMAX imaging method from Core

Laboratories was used to to observe residual oil distribution across the core. During open hole

log analysis, different rock type are identified using rock type flag and probabilistic flag.

Conclusion reached:

Residual oil saturation values might be different for different rock types and area although not

significantly. The different methods of cased hole and open hole logs give a consistent result

with core analysis data.

Comments:

The paper shows how to integrate different type of measurement and relates the result with

time. However this study rely heavily on cased hole logs data which might not be available for

typical North Sea wells which has subsea completion.



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A1.6 SPE 16471 WETTABILITY LITERATURE SURVEY-PART 6: THE EFFECTS OF WETTABILITY ON

WATERFLOODING

Authors: Anderson, W. G.

Contribution:

The paper is a comprehensive literature survey on the effect of wettability to waterflooding.

The author compiled and reviewed various core water flood experiments and observes the impact

of changing wettability to waterflood behaviour. Different wettability state including water wet,

oil wet and mixed wet are discussed and compared to make clear understanding on how different

wetting state could affect oil recovery.

Objective of Paper:

The paper aims to summarise various experimental result on core waterflood study and

discuss the relation of different wetting phase to residual oil saturation, breakthrough time,

cumulative oil recovery, and the period of two phase flow after breakthrough. The paper also

discuss the effect of viscosity ratio on recovery factor and the effect of core handling and

cleaning to the wetting state of the core plugs.

Methodology used:

The author conducted literature survey on various technical publications about core water

flood analysis.

Conclusion reached:

In a strongly water wet sample, most of the oil is produced before breakthrough followed by

small or no oil production afterwards. In water wet system, water act as a continuous phase on

the pore surface making the water sweep become more effective. In the oil wet system, earlier

breakthrough is observed followed by two phase flow for a long period of time. More oil could

be recovered when more PV of water is injected. Oil wet sytem shows lower recovery factor

compared to water wet system. In a mix wet system, water is trapped in the smaller pore which

has water wet behaviour, while oil is trapped in the bigger pore which has oil wet behaviour.

When it comes to water flooding, mix wet system could achieve a very low residual saturation

since most of the oil will be swept out from the bigger pores.

Comments:

The paper provide comprehensive discussion on the effect of different wettability system

could impact the performance of water flood process.

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A1.7 SPWLA 1986-VXXVIIN5A3 SENSITIVITY ANALYSIS OF THE PARAMETERS IN ARCHIE''S

WATER SATURATION EQUATION

Authors: Chen, H. C. & Fang, J. H.

Contribution:

The paper provide a full sensitivity analysis of the Archie water saturation equation, assuming

all six variables in the equatuion to be error prone. The analysis was performed in two models,

(1) Equal uncertainty and (2) unequal uncertainty. The method proposed in the paper enables us

to quantify the error contribution of each parameter. Sensitivity analysis become important when

the measurement of each Archie parameter are not always accurate and highly depends on the

measurement and interpretation technique.

Objective of Paper:

The paper aims to provide simple and direct calculation technique to quantify error in each

Archie parameter by introducing fractional error contribution of each constant. The author tried

to develop a simpler approach of sensitivity analysis for Archie equation compared to the more

complicated Monte Carlo analysis.

Methodology used:

The equation was derived based on standard analysis of errors developed by Bevington (1969)

and then created random variables for each of Archie constants.Total variances of Sw is devided

into six individual variances to create fractional error contribution parameter.

Conclusion reached:

Sensitivity analysis is a study of the sensitivity of a system’s response to various disturbances

in the system. This type of study is essential to well log analysis where algebraic equation such

as Archie call for several parameter whose values may not be accurately known. This method is

found to be as accurate as Monte Carlo simulation. However the time needed for calculation is

much less than Monte Carlo analysis.

Comments:

The paper provide a simple approach to conduct sensitivity analysis for Archie equation

which is essential for the study objective of this project.





A1.8 SPWLA 2004-UUU EVALUATION OF RESIDUAL OIL SATURATION IN THE

BALMORAL FIELD (UKCS)

Authors: Conti, F. & Bona, N.

Contribution:

The paper provide of a case study for residual oil calculation in Balmoral Field in the UK

North Sea using integrated core and log analysis in the swept zone. The author shows that not all

the laboratory analysis result is valid to be taken as a reference for Sor study due to the

associated uncertainty from laboratory procedure and sample condition.

Objective of Paper:

The paper was attempted to investigate the true value of residual oil saturation in Balmoral

Field operated by ENI UK Ltd. The study was triggered by a suspicion that the current Sor value

used in the reservoir simulation might be too high due to the field performance which always

higher than the prediction. It aims to quantify residual oil saturation from logs obtained across

the swept zone of the reservoir,

Methodology used:

The author used open hole logs data which obtained from newly drilled well that exhibit

swept zone. Residual oil saturation was calculated using Archie formula at the swept zone which

exhibit higher resistivity values compared to the water zone. The uncertainty in calculated water

saturation was analyzed using deterministic methods.

Conclusion reached:

True residual oil saturation in Balmoral was find much lower than the one currently used in

the reservoir simulation. The change of Sorw values in simulation improved history matching

which later on provide a better prediction for the reservoir performance.

Comments:

The paper shows a simple yet reliable method of quantifying residual oil saturation from open

hole log data and special core analysis result which is reliable and accurate.

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12

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A1.9 SPE 39038 OPTIMAL DESIGN AND PLANNING FOR LABORATORY COREFLOODS

Authors: dos Santos, Renato L. A., Bedrikovetsky, P. & Holleben, Carlos R.

Contribution:

The paper provides a method to quantify different effect from laboratory experiments in core

water flood study. The method proposed by the paper could be used for planning a core water

flood test to get a reliable result.

Objective of Paper:

The paper pointed out the conditions that should be fulfilled in order an unsteady state method

of relative permeability measurement becomes valid. The criteriais based on the physical

similarity to waterflooding conducted in the reservoir. This criteria will avoid a laboratory

experiments result from becoming invalid due to numerous effect of different parameters.

Methodology used:

The work of Bedrikovetsky et al for planning the core flood test based on the Barenblatt’s non

equilibrium theory was used a a basis. The proposed method calculates the capillary number,

capillary viscous ratio, and gravity viscous ratio as a screening criterion.

Conclusion reached:

Sample lengths and fluid velocity is the most important factor in order to get a reliable core

flood result. More criteria should be fulfilled when the displacement is using miscible fluid or

EOR fluid such as surfactant or polymer.

Comments:

The method describe in the paper could be used to screen out and select for a reliable

laboratory core flood result from the existing database. This step will be the first step for a sor

determination from core analysis.

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A1.10 SPE 17686 RESIDUAL OIL SATURATIONS DETERMINED BY CORE ANALYSIS

Authors: Kennaird, T.

Contribution:

The paper discussed the result of laboratory oil displacement experiments using water and gas

which conducted for different purposes such as flood analysis and relative permeability

measurement for various lithologies. The experiments were conducted in different conditions

such as steady state, unsteady state, and centrifuge at both reservoir and ambient temperature.

Objective of Paper:

The paper investigate the value of residual oil saturation which resulted from different type of

measurement and see the impact of different lithology, viscosity ratio, rate, temperature, and

petrophysics feature of each core samples.

Methodology used:

The author conducted water flood experiments to different lithology of core sample in both

room and reservoir temperature using different value of viscosity ratio. The relation of residual

saturation to petrophysical parameter is bein investigated.

Conclusion reached:

Water injection seems to lead to a lower residual oils aturation than gas injection, In assessing

residual oil saturation data, consideration should be given to the test methods. Given the possible

influence of rock water interaction and oil viscosity on oil recovery, a waterflooding test used to

determine residual saturation should preferably reflect what happen in the reservoir.

Consideration should be given to whether or not the reservoir characteristics favour oil

displacement by gravitational forces. Trends exist between residual oil saturation, initial water

satiration and permeability.

Comments:

The paper gives a valuable insight of residual oil determination from various laboratory

methods.


14

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A1.11 SPE 3785 RESERVOIR WATERFLOOD RESIDUAL OIL SATURATION FROM LABORATORY

TESTS

Authors: Rathmell, J. J., Braun, P. H. & Perkins, T. K.

Contribution:

The paper presents the results of theoretical and experimental study of laboratory waterflood

and core saturation data which was obtained using water based mud. The paper used previously

published information and its own experimental result.

Objective of Paper:

The paper aims to compare different type of residual saturation measurements by core flood

and dean and stark method on a core sample cutted using water based mud.

Methodology used:

The authors uses fresh core with different type of wettability to conduct laboratory water

flood. Routine core analysis was used as a comparison after the data being adjusted with

bleeding and shrinkage factor.

Conclusion reached:

Laboratory measurement of oil bleeding and shrinkage during the lifting of a core may be

used to adjust the surface oil saturation of the core to reflect the oil saturation before lifting. The

change in oil saturation due to bleeding was found to be about 10% PV for the reservoir cores

which were used in the study. In order to get results representative of the reservoir, laboratory

waterflood must sometimes be carried out using live fluids at reservoir pressure and temperature.

Rocks characteritized as weakly water wet by imbibitions behaviour may have lower residual oil

saturation both at breakthrough and at flood out than rocks that are strongly water wet.

Comments:

The paper provide an understanding of the importance of using live reservoir fluids and

conduct the experiments at reservoir temperature and pressure to match the actual condition of

waterflood in the reservoir.




A1.12 SPE 3786 CORE AND LOG DETERMINATION OF RESIDUAL OIL AFTER WATERFLOODING -

TWO CASE HISTORIES.

Authors: Strange, L. K. & Baldwin, W. F.

Contribution:

This is a case study of two fields under waterflood which is assessed for tertiary recovery. The

method of determining residual oil saturation comes from core and log analysis. The paper

investigate the effect of mobile oil and water which lead to flushing during coring operation

which lead the measurement become invalid.

Objective of Paper:

The paper studies two field which are Loudon and Loma Novia field which both under

waterflooding. It used log and core data to assess the potential of two fields to undergo tertiary

recovery

Methodology used:

The paper observe the effect of coring fluid the the measurement of residual oil saturation.

The obtained log data is compared to core measurement to find the degree of flushing and look at

the different result of flushed and non flushed cores.

Conclusion reached:

Conventional rotary cores appear to be superior to cable tool cores from the stand point of

core flushing. While the rubber sleeve core barrel can provide good recovery of unconsolidated

cores, there is evidence that flushing may be more severe than in better consolidated cores.

Electric log techniques proved superior to coring and core analysis to determine oil in place

saturation under the dual mobility conditions.

Comments:

The paper shows the importance of electric log measurement to provide valid saturation

measurements when the core sample are found to be flushed due to the existence of mobile oil

and water during the coring operation.


16

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A1.13 SPE 3795 DETERMINATION OF RESIDUAL OIL SATURATION FROM TIME-LAPSE PULSED

NEUTRON CAPTURE LOGS IN A LARGE SANDSTONE RESERVOIR.

Authors: Syed, E. U., Salaita, G. N. & McCaffery, F. G.

Contribution:

The paper shows the utilization of Pulsed Neutron Logs to investigate the relation of residual

oil saturation to the amount of water sweep in the reservoir. The in situ measurement provides a

reliable result since it is free from potential error during the laboratory experiments.

Objective of Paper:

Saturation behind casing is a useful data to monitor the movements of flood front and

unswept zones during waterflood process. The paper describe quantitative determination of

residual oil saturation in water swept zones from numerous wells representing major protions of

the field where water advancement had been dominant.

Methodology used:

The author carried out the work by utilizing PNC log transform developed from the well test

data. The transform was made easier die to the equivalence of the borehole sizes. The paper also

assess the uncertainty in Sor calculation by calculating the total error calculated in water

saturation.

Conclusion reached:

Error analyses suggest that the overall uncertainty in saturations is ranges with porosity

uncertainty being a major factor affecting the analysis results. Errors in initial water saturation

calculations from open hole logs were not included in the uncertainty assessments. The use of

test well PNC log transform provided effective means for time lapse analysis. Formation sigma

traces from early generation tools were converted to equivalent traces for a more accurate tool.

Higher Sor values generally corresponded to deteriorating reservoir rock quality.

Comments:

The paper shows that Sor could be accurately measured using PNC log, and with periodic

survey, a relation of Sor with the function of time could be generated.




A1.14 SPE 77545 A UNIFIED THEORY ON RESIDUAL OIL SATURATION AND IRREDUCIBLE WATER

SATURATION.

Authors: Valenti, Nick P., Valenti, R. M. & Koederitz, L. F.

Contribution:

The paper pointed out several classic assumptions used in approximating reservoir recovery in

a small reservoir which is no longer applicable when is used in bigger reservoir. The unified

theory of residual saturation provides a general approach for different type of reservoirs.

Objective of Paper:

The paper define residual oil saturation and irreducible water saturation in the context of

saturation after displacement process is over. It considers capillary force in different type of

laboratory measurement such as drainage/imbibitions capuillary pressure curves, coreflood, and

centrifuge test.

Methodology used:

The author compiles different publication in residual saturation and irreducible oil saturation

measurements and discuss how different condition could lead to different result and might lead

to the wrong decision for tertiary recovery.

Conclusion reached:

Centrifuge tests are recommended over core flood test in terms of obtaining residual oil

saturations and irreducible water saturations. However the maximum centrifuge wpeed must be

correspond with the maximum capillary pressure encountered in the reservoir. The typical

centrifuge and core flood teset result can be reasonably representative for reservoirs with

minimal closure. Using conservative residual oils aturation has yielded an optimistic estimate of

sweep efficiency, therefore forecasting technique such as reservoir simulation model are likely to

underestimate the quantitiy of mobile oil remaining in the reservoir.

Comments:

The current old assumption of residual oil saturation tends to underestimate the true potential

of tertiary oil recovery.



18

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A1.15 SPE 22903-MS DETERMINING EFFECTIVE RESIDUAL OIL SATURATION FOR MIXED

WETTABILITY RESERVOIRS: ENDICOTT FIELD, ALASKA.

Authors: Wood, A. R., Wilcox, T. C., MacDonald, D. G., Flynn, J. J. & Angert, P. F.

Contribution:

The paper explains the significance of mixed wettability to effective water saturation, in

which the value is a function of the amount of PV of water injected.

Objective of Paper:

The paper discuss the residual oilsaturation in Endicott field Alaska which has mix wettability

type rock. The particular wettability is expected to behave differently from the commonly known

water and oil wet reservoir.

Methodology used:

The author used core water flood experiments to observe the behaviour and oil recovery after

breakthrough and also the duration of two phase flow afterwards.

Conclusion reached:

Mix wet reservoir exhibit lower residual saturation com[pared to strongly oil wet and strongly

water wet samples. This is due to the trapping mechanism of water and oil which is trapped in

different size of pores.

Comments:

This paper give a case study of mix wettability reservoir which undergone waterflood.

Previous studies normally only cover

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Integration of Residual Hydrocarbon Saturations From Well Logs GGiri Aridiita ta Identified Swept Zones With Relative Permeability and Core Saturation Data MSc in Petroleum Engineering 2009/2010

APPENDIX – 2 Field Description Figures APPENDIX – 3: Archie Constants CalculationAPPENDIX – 2: Field Description

20

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APPENDIX 2: APPENDIX - 2 FField Description FiguresDescriptions

\The Gryophon Field is located in the South Viking Graben area of the North Sea within Blocks 9/18b and the extreme

southern part of 9/18a, located approximately

Figure A 1 Net Sand Map of Gryphon Area with the Locations of Cored Wells

5597.83 ’ 5600.67 ’ 5603.58 ’ 5606.3

3 ’ 5609.17 ’

5600.67 ’ 5603.58 ’ 5606.33 ’ 5609.17 ’ 5611.88 ’

5597.83 ’ 5600.67 ’ 5603.58 ’ 5606.33

’ 5609.17 ’

5600.67 ’ 5603.58 ’ 5606.33 ’ 5609.17 ’ 5611.88 ’

White Light Core Photograph

Ultra Violet Light Core Photograph

5597.83 ’ 5600.67 ’ 5603.58 ’ 5606.3

3 ’ 5609.17 ’

5600.67 ’ 5603.58 ’ 5606.33 ’ 5609.17 ’ 5611.88 ’

5597.83 ’ 5600.67 ’ 5603.58 ’ 5606.33

’ 5609.17 ’

5600.67 ’ 5603.58 ’ 5606.33 ’ 5609.17 ’ 5611.88 ’



5597.83 ’ 5600.67 ’ 5603.58 ’ 5606.33

’ 5609.17 ’

5600.67 ’ 5603.58 ’ 5606.33 ’ 5609.17 ’ 5611.88 ’

5597.83 ’ 5600.67 ’ 5603.58 ’ 5606.33

’ 5609.17 ’

5600.67 ’ 5603.58 ’ 5606.33 ’ 5609.17 ’ 5611.88 ’



5597.83 ’ 5600.67 ’ 5603.58 ’ 5606.3

3 ’ 5609.17 ’

5600.67 ’ 5603.58 ’ 5606.33 ’ 5609.17 ’ 5611.88 ’

5597.83 ’ 5600.67 ’ 5603.58 ’ 5606.33

’ 5609.17 ’

5600.67 ’ 5603.58 ’ 5606.33 ’ 5609.17 ’ 5611.88 ’



Figure A 2 Core photograph of Well 9/18b-7 Showing Oil Bearing Sandstone

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APPENDIX – 1: Critical Literature Review2 Field Description Figures1: Critical Literature Review 21


Figure A 3 Type Log of Gryphon Area Showing Balder Massive Sandstone





22



-6100

-6000

-5900

-5800

-5700

-5600

-5500

-5400

-5300

-5200

2460 2510 2560 2610 2660 2710 2760

GOC -5541ft ss

OWC -5731ft ss

Gas Gradient

0.03 psi/ft

Oil Gradient 0.37

psi/ft

Water Gradient

0.45 psi/ft

Figure A 4 Composite RFT Data from Gyphon

Figure A 6 Kv/Kh Cross Plot of Balder Massive

Sandstone

Composite RFT Data from Gyphon Wells

Figure A 5 Porosity Permeability Cross Plot of

Balder Massive Sandstone

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Figure A 8 West East Seismic Cross Section of Gryphon Field

Figure A 7 North South Schematic Cross Section of Gryphon Field






24



Figure A 10 North South Schematic Cross Section of Maclure Field

Figure A 9 North South Schematic Cross Section of Harding and Tullich Field






Formatted ...

Table A 11 Reservoir Oil Properties

Gryphon Harding Maclure Tullich

Stock tank oil gravity (API) 21.5 19.3 26.5

Bubble point (psia) @Pb 2504 2504 2503

Rs (scf/stb) @Pb 259 254 330

Bo (rb/stb) @Pb 1.114 1.118 1.114

Oil compressibility (1/psi) (3000 to Pb) 3.92e-06 6.05e-6 7.52e-06

Reservoir oil viscosity 6.7 9.7 5.8

Table A 22 Formation Water Properties

Well

9/18b 7 10 11 12 13 13Z 14 14Y 14Z 16 17 17X 17Y 17Z

Sample

Source RFT RFT RFT RFT RFT RFT RFT RFT RFT RFT RFT RFT RFT RFT

Specific

Gravity 1.049 1.046 1.047 1.045 1.05 1.048 1.04 1.047 1.05 1.046 1.052 1.052 1.052 1.05

Resistivity

@ 60oF

0.142 0.132 0.131 0.14 0.142 0.141 0.135 0.135 0.135 0.138 0.146 0.143 0.132 0.139

pH 6.97 7.03 7.34 7.33 7.33 7.08 8.41 6.95 6.92 7.55 7.13 7.07 8.1 7.68




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Formatted Table



Formatted ...

Formatted


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Formatted


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Formatted


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APPENDIX – 3: Log AnalysisAPPENDIX – 3: Archie Constants CalculationAPPENDIX – 2: Field Description

26



Saturation Exponent Histogram (n)

0

1

2

3

4

5

6

11.

31.

61.

92.

22.

52.

83.

13.

43.

7 44.

34.

64.

9

Saturation Exponent (n)

Fre

qu

en

cy

0

10

20

30

40

50

60

70

80

90

100

Pe

rce

nta

ge

n

Cummulative frequency

Cementation Factor Histogram (m)

0

1

2

3

4

5

6

7

8

1.51.

531.

561.

591.

621.

651.

681.

721.

751.

781.

811.

841.

87 1.9

1.93

1.96

1.99

Cementation Factor (m)

Fre

qu

en

cy

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

Pe

rce

nta

ge

m

Cummulative frequency

APPENDIX - 3 Archie Constants Log AnalysisCalculation

Figure A 11 Histogram of Core Derived Cementation Factor

Figure A 12 Histogram of Core Derived Saturation Exponent


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APPENDIX – 3: Log AnalysisAPPENDIX – 3: Archie Constants Calculation 27


Histogram of COMPOSITE.RWAWell: 19 Wells

Range: All of WellFilter: REFERENCE.TVDSS>5731&COMPOSITE.PHIE>0.1

0.0

0.2

0.4

0.6

0.8

1.0

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.0

1

0.1 1

Percentiles:

5% 0.0324150% 0.0583395% 0.10907

Statistics:

Possible values 7359Missing values 0Minimum value 0.00913Maximum value 15.31219Range 15.30306

Mean 0.07260Geometric Mean 0.05809Harmonic Mean 0.05367

Variance 0.11079Standard Deviation 0.33285Skewness 40.53374Kurtosis 1733.51089Median 0.05833Mode 0.06166

7359

7344

3 12

Figure A 13 Histogram of Log Derived Apparent Water Resistivity (Rwa) Formatted: Caption, Centered, Keepwith next



28



Log Analysis

APPENDIX 3:

Figure A 14 Harding Well 9/23b-A29 Open Hole Log

Formatted: Centered



APPENDIX – 3: Log AnalysisAPPENDIX – 3: Archie Constants Calculation 29


Figure A 1515154 HardingGryphon Well 9/1823b-30AA29 Open Hole Log




30



Histogram of COMPOSITE.RWAWell: 19 Wells

Range: All of WellFilter: REFERENCE.TVDSS>5731&COMPOSITE.PHIE>0.1

0.0

0.2

0.4

0.6

0.8

1.0

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.0

1

0.1 1

Percentiles:

5% 0.0324150% 0.0583395% 0.10907

Statistics:

Possible values 7359Missing values 0Minimum value 0.00913Maximum value 15.31219Range 15.30306

Mean 0.07260Geometric Mean 0.05809Harmonic Mean 0.05367

Variance 0.11079Standard Deviation 0.33285Skewness 40.53374Kurtosis 1733.51089Median 0.05833Mode 0.06166

7359

7344

3 12

Formatted: English (U.S.), Checkspelling and grammar


Formatted: Section start: New page


APPENDIX – 3: Archie Constants 4: Core Analysis DataCalculation 31


Harding SCAL Distribution

FRF @ NOB Pressure, 29

FRI @ NOB Pressure, 14

Water-Oil PC, 6

Mercury Injection, 6

Cation Exchange

Capacity, 7

Gas-Oil Rel Perm, 12

Water-Oil Rel Perm, 13

Waterflood Susceptibility

Analysis, 6

Por as Function of

Overburden, 7

XRD Analysis, 7

Por-perm @ Overburden

Pressure, 10

Air Brine PC, 7

PV Compressibility, 4

FRF @ NOB Pressure

FRI @ NOB Pressure

Water-Oil PC

Mercury Injection

Air Brine PC

Cation Exchange Capacity

Gas-Oil Rel Perm

Water-Oil Rel Perm

PV Compressibility

Waterflood Susceptibility Analysis

Por as Function of Overburden

XRD Analysis

Por-perm @ Overburden Pressure

SCAL Wells

Gryphon, 7

Maclure, 2

Tullich, 1

Harding, 4

Gryphon

Maclure

Tullich

Harding

Gryphon SCAL Distribution

Oil/Water Rel Perm, 55

Gas/Oil Rel Perm, 29

Wettability, 71

Electrical properties, 87

Waterflood Susceptibility,

33

Irreducible Sw, 18

Uniaxial & Hydrostatic

Compressibility, 5

Por-perm at Overburden,

29

Capillary pressure, 35Oil/Water Rel Perm

Gas/Oil Rel Perm

Wettability

Electrical properties

Waterflood Susceptibility

Irreducible Sw

Uniaxial & Hydrostatic Compressibility

Por-perm at Overburden

Capillary pressure

APPENDIX 4: APPENDIX - 4 Relative Permeability Data RefinementCore

Analysis

Figure A 1616187 Pie Chart of the Number of Plugs for Different SCAL Analysis in Harding

Field

Figure A 1818168 Pie Chart of the Number of SCAL Wells

Figure A 1717176 Pie Chart of the Number of Plugs for Different SCAL Analysis in Gryphon

Field

Formatted: Heading 1, Don't keepwith next

Formatted

Field Code Changed

Formatted: English (U.S.), Checkspelling and grammar




APPENDIX – 4: Core Analysis DataAPPENDIX – 45: Relative Permeability Data Refinements

32


Maclure SCAL Distribution

Sw Irreducible, 17

AMOTT Wettability, 6

Oil/Water Rel Perm, 13FRF @ Overburden

Pressure, 9

Capillary Pressure, 9

FRI @ Overburden

Pressure, 4


Kw @ Overburden

Pressure, 5

Porosity @ Overburden

Pressure, 5 Sw Irreducible

AMOTT Wettability

Oil/Water Rel Perm

FRF @ Overburden Pressure

Capillary Pressure

FRI @ Overburden Pressure

PV Compressibility

Kw @ Overburden Pressure

Porosity @ Overburden Pressure

Figure A 1919189 Pie Chart of the Number of Plugs for Different SCAL Analysis in Maclure

Field

Tullich SCAL Distribution

FRF @ Ambient Pressure,

4

FRI @ Overburden

Pressure, 4


Air-Brine Capillary

Pressure, 4

Oil-Water Rel Perm, 8

Core Saturation, 8

Mercury Injection, 4

X-ray Diffraction, 4

Cation Exchange

Capacity, 4FRF @ Ambient Pressure

FRI @ Overburden Pressure

PV Compressibility

Air-Brine Capillary Pressure

Oil-Water Rel Perm

Core Saturation

Mercury Injection

X-ray Diffraction

Cation Exchange Capacity

Figure A 20201209 Pie Chart of the Number of Plugs for Different SCAL Analysis in Tullich

Field




APPENDIX – 3: Archie Constants 4: Core Analysis DataCalculation 33


Dean Stark Histogram

0

2

4

6

8

10

12

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Sor (%)

Fre

qu

en

cy

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

Frequency

Cumulative %

Figure A 2121210 Histogram of Oil Saturation From Dean Stark Analysis


Integration of Residual Hydrocarbon Saturations From Well Logs Giri Aridiita ta Identified Swept Zones With Relative Permeability and Core Saturation Data MSc in Petroleum Engineering 2009/2010

APPENDIX – 5: Relative Permeability Data Refinements APPENDIX – 45: Relative Permeability Data

Refinements 34


0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00K

r

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

APPENDIX 5: Relative Permeability Data Refinement

Fig. A 1 Rel Perm Data from

Sample 17-87VA


Sample 17-94VC


Sample 17-120VB


Sample 17-134VA


Sample 14-A3


Sample 12-229VA


Sample 14-D2


Sample 13-Test


Sample 12-Test


Sample 14-B3

Formatted: Left: 3.05 cm, Right: 0.95 cm, Top: 1.52 cm, Bottom: 1.52cm, Width: 29.7 cm, Height: 21 cm

Formatted: Caption

Formatted: Caption

Formatted: Caption

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Formatted: Caption

Formatted: Caption

Integration of Residual Hydrocarbon Saturations From Well Logs Giri Aridita Identified Swept Zones With Relative Permeability and Core Saturation Data MSc in Petroleum Engineering 2009/2010Integration of Residual Hydrocarbon Saturations From Well Logs Giri Aridita Identified Swept Zones With Relative Permeability and Core Saturation Data MSc in Petroleum Engineering 2009/2010

APPENDIX – 5: Relative Permeability Data Refinements APPENDIX – 5: Sector Model

35

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`


Sample 12-206V


Sample 12-82V


Sample 11-10V


Sample 11-49V


Sample 11-105V


Sample 11-178V


Sample 11-44V


Sample 11-109V


Sample 11-176V


Sample 11-15V

Formatted: Caption

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Formatted: Caption



Refinements 36


0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`


Sample 11-16V Fig. A 10 Rel Perm Data from

Sample 11-89VA


Sample 11-13V


Sample 11-15V2


Sample 11-16V2


Sample 11-11


Sample 11-12


Sample 11-16


Sample 11-17


Sample 11-50

Formatted: Caption

Formatted: Caption

Formatted: Caption

Formatted: Caption

Formatted: Caption

Formatted: Caption

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37

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0

Kr

Sw

Curve Refinement

Krw

Kro

Krw, ref.

Kro, ref.

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`


Sample 11-105


Sample 11-51


Sample 11-106


Sample 11-108


Sample 11-109


Sample 11-143


Sample 11-144


Sample 11-167


Sample 11-168


Sample 10-13B

Formatted: Caption

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Refinements 38


0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

Krw, ref.

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`


Sample 7-9D


Sample 7-8D


Sample 7-7D


Sample 7-6D


Sample 7-5D


Sample 7-4D


Sample 7-3D


Sample 7-2D


Sample 7-1D


Sample 10-14A

Formatted: Caption

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39

0.00

0.10

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0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Kr

Sw

Curve Refinement

Krw

Kro

`


Sample 7-10D


Sample 12-205VA Formatted: Caption

Formatted: Caption


APPENDIX – 5: Relative Permeability Data Refinements

APPENDIX – 5: Sector Model 41

APPENDIX - 5 Core Analysis

Routine core analysis including core gamma measurement, core slabbing, core sampling core cleaning and drying, porosity

and permeability measurement, and saturation determination by both retort distillation method and Dean and Stark Analysis.

The plugs are cut about 2-3 inches long and 1.5 inch in diameter in SCAL analysis before loaded into hydrostatic core holder

where overburden pressure were applied. Subsequently each plug was flushed with 200 cP bland mineral oil at 200C and

followed by flushing with 20 cP mineral oil to determine irreducible water saturation and permeability to oil (Kro at Swc).



Formatted


APPENDIX – 6: Buckley Leverett Calculation 42


APPENDIX 6: APPENDIX - 6 Buckley Leverett Calculations

Figure A 222221 Workflow of Buckley Leverett Analysis to Calculate Oil Saturation as A Function of PV Water

Sweep





APPENDIX – 7: Impact of SORW to Recovery Prediction and History Match 43

APPENDIX 7: APPENDIX - 7 Impact of SORW to Recovery Prediction and History Match

Figure A 242422 Comparison of Field Oil Production Rate from Different Sor Cases with Actual Production Rate

Figure A 232323 Comparison of Field Water Production Rate from Different Sor Cases with Actual Production Rate



Formatted




APPENDIX – 7: Impact of SORW to Recovery Prediction and History Match 44


Figure A 252525 Comparison of Field Gas Production Rate from Different Sor Cases with Actual Production Rate

Figure A 262624 Comparison of Field Water Cut Production Rate from Different Sor Cases with Actual Production

Rate



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