thesis presentation_ final defence

Reserve Estimation of Titas Gas Field Insight From Log Data and Production Data

Presented By

Sharmin Ahmed

Reg.: 2005336029

Supervisor

Dr. Md. Farhad HowladarAssistant Professor

Department of Petroleum & Mining EngineeringShah jalal University of Science & Technology, Sylhet.

Contents

Reserve Estimation of Titas Gas Field Insight From Log Data and Production Data 2

Description of the Study Area.

Objectives

Methodology

Results

Comparison of results

Discussion

Problems

Comment

Study Area

3

Location This field was discovered by Pakistan Shell well company in 1962.

Titas Gas Field is situated in Brahmanbaria district. And it is about

50 miles east of Dhaka city.

The area lies in Block-12 under PSC (Production Sharing Contract)

for petroleum exploration.

Titas Gas Field is the largest anticlinal closure so far discovered in

Bangladesh.

The depth of the gas reservoirs are range from 2616 to 3124m

below the surface.


Study Area

4

Maps : Location map of Titas structure in the Petroleum Exploration Blocks of Bangladesh. (Source- Petrobangla)


Titas gas field

Objectives

5

Main Objectives– To know the study area

– To estimate Gas initially in place (GIIP)

– To estimate the Recoverable reserves and

– Recovery factor (RF) of Titas gas field.

– To obtain the result of the above parameters the following

methods are used:

– Volumetric method

– Conventional material balance method

– Flowing gas material balance method

– To compare the results of all methods.Reserve Estimation of Titas Gas Field Insight From Log Data and Production Data

Geology

6

Geology and Stratigraphy of Titas Gas Field:

Titas structure is located in the north-eastern part of the Deep

(Geosyncline) Basin.

Also the Titas gas field lies in the Fold Belt area which is a part of

Deep Basin.

We know that the Fold Belt area is characterized by folding of the

sedimentary layers into a series of anticlines and synclines.

As the gas field lies over the north-eastern part of the Fold Belt

also known as Sylhet trough, so this part is comprised with very

high amplitude hills.


Geology

Maps: Physiographic and Tectonic map of Bangladesh showing the position of Titas structure (Source- Petrobangla)

7Reserve Estimation of Titas Gas Field Insight From Log Data and Production Data

TITAS Structure

Geology

8

Fig: Spatial orientation of major productive sands (Source- Petrobangla)


Geology

9

Figure: Sand wise structure of different wells (from well no 1-16) of Titash Gas Field.(source Petrobangla)


A1 Sand

A2 Sand

A3 Sand

A4 Sand

C Sand

B Sand

Geology


A1 sand: Yellow colour represents A1 sand. Shale mixed sand and not very good quality sand. A few amount of hydrocarbons are deposited here.

A2 sand: Ash colour represents A2 sand. Very good quality sand and it is he main sand of Titash Gas Field. Here the sand grains are equally distributed as a result porosity is very high. A huge amount of hydrocarbons are deposited here.

A3 sand: Brown colour represents A3 sand. Good quality sand and main sand of Titash Gas Field. A huge amount of hydrocarbons are deposited here.

Area extension is larger in A2 and A3 sand and major gas sand of gas field.

Geology


A1 A2 and A3 sand layers are isolated by shale.

B sand: Blue colour represents B sand. Minor sand layer of Titash Gas Field.

C sand: Red colour represents C sand. Minor sand layer of gas field.

A few amount of hydrocarbons are deposited in B and C sand.

Methodology


To achieve the mentioned objectives of my research

the following methods are adopted:

Volumetric Estimate

Material Balance Estimate

Conventional Material Balance Estimate

Flowing Gas Material Balance Estimate

Methodology

13

• Early stage of the reservoir development

• Geology, geophysics rocks & fluid properties needed• Not time dependent• No production data is required• After discovery, during initial delineation and

development of a field volumetric estimation is the key to estimation

• It is a useful tool for calculating the gas in place at any time; considerably it has reasonable utility in estimating gas reserves.


Volumetric Study

Methodology


Volumetric Study

Figure : Porosity Vs. Depth Plot, Titas Gas Field

Methodology

15

G = 43,560AhΦ(1− Swi)/ Bg

• G - in-place gas, standard cubic feet

• A - reservoir area, feet2

• Ф - reservoir porosity, fraction

• Swi -connate water saturation

• (1-Swi ) - gas saturation• Bg - gas formation volume factor• Where, Bgi=0.02828ZiT/Pi,ft3/scf


Area,Thikness

Porosity,Saturation

Formation volume factor

Structure, contour map

Log and core analysis

PVT correlation

Variables

Methodology

Sources

Data and sources of volumetric study


Methodology


(Sub-Surface )

Proposed Well Surface (Present)

Existing Well

Proposed Well Sub-Surface (Present)

(Surface)

Proposal for new wells

Figure: Area estimation (Source Petrobangla)

18

Methodology


Material Balance Method

Assumptions:

Homogeneous Tank (Same Rock and Fluid Properties) Fluid Production at a Single Point No Direction to Fluid Flow

Applications:

Original Oil or Gas-In-Place Producing Mechanism Production Performance

Methodology


P/Z =(1-Gp/G) Pi/Zi

Gp = cumulative gas production, scf

G =original gas in place, scf

P =pressure, psia

Pi =initial pressure, psia

Z = compressibility at pressure

Zi = compressibility at initial pressure

Gas Material Balance Equation

Methodology


Conventional material balance analysis

• Basis: Shut in reservoir pressure

• Based on the obtaining a straight line on P/Z versus Gp to estimate GIIP

• Requires fully build up reservoir pressure , obtained by shutting in the wells for few days.

Methodology


Reserve Estimates Involve some Degree of Uncertainties:

• Dependent upon reliability of the available data• Interpretation of the data• Techniques used

Results


Calculated Reserves:Volumetric estimation:

Formula, GIIP= 43560*AhΦ(1-SWC)*1/Bgi (scf) ( Dake L. P., Fundamentals of Reservoir Engineering)

So gas initially in place in Titas gas field is

SAND GIIP (Tcf)

A 5.68

BC 0.523

GIIP in Titas gas field 6.2065

Table: Total GIIP in Titas gas field.

Results


Conventional Method:

The conventional method shows that the gas initially in place in A sand is 9.7 Tcf.

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100000

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Cummulative production,Gp(bcf)

p/z

,psia

A sand reserve using Shut in Reservoir Pressure

y = - 0.43*x + 4.2e+003

data 1

linear

Gas initially inplace,GIIP, 9.6 TCF

Figure : GIIP in A sand using Conventional method. (Source- Petrobangla)

Results


Conventional Method: For BC sand the gas initially in place is 1.555 Tcf.

0 200 400 600 800 1000 1200 1400 1600 1800 20000

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Cummulative production, Gp(bcf)

p/z

Reserves in B&C Sand using BHP

y = - 2.8*x + 4.4e+003

data 1

linear

Figure: Gas initially in place in BC sand using the conventional method.

Results


Result of the conventional method:

Table: Gas initially in place using Conventional Material Balance method.

NAME OF THE SAND GAS INITIALLY (Tcf)

A 9.7

BC 1.555

TOTAL 11.255

Results


Flowing head pressure method:

So the well wise GIIP in A sand using the Flowing well head pressure are as follows:

Table: GIIP in A Sand using the flowing well head pressure.

WELL NAME (A SAND) GAS INITIALLY IN PLACE (Bcf)

T1A 890T2A 940T3A 710T4A 800T5A 910T6A 735T7A 790T11A 1360T12A 330T13A 450T14A 290T15A 395T16A 830Total gas initially in place in A SAND

9430 (Bcf) or 9.43 Tcf

Results


Gas initially in place in Titas gas field using flowing well head pressure:

Table: Total gas initially in place in Titas gas field using Flowing well head pressure.

SAND NAME GAS INTIALLY (Tcf)

A 9.43

BC 1.6

Total gas initially in place in Titas gas field

11.03

Results


Reserves, remaining reserve and recovery factor:

Conventional method:

A sand:For A sand the gas initially in place is 9.7 Tcf.Up to April 2011 the cumulative production from A sand was 2.4782302 Tcf. Reserve at the abandonment P/Z of 1000 psia is 7.25Tcf .So the remaining reserve for this location 4.77Tcf.The recovery from A sand till April 2011 is (2.4782302/9.7) or 25.51%

BC Sand:The gas initially in place is 1.555 Tcf .Up to April 2011 the cumulative production from BC sand was .6667072 Tcf.Reserves at the abandonment P/Z of 1000 psia is 1.2Tcf.So the remaining reserve for this location is 0.53 Tcf.The recovery from BC sand till April 2011 is (.6667072/1.555) or 42.83%

Results


Present status of Titas gas field:

Table : Present status of Titas Gas field.

SAND GIIP (Tcf)

Reserves (Tcf) at abandonment P/Z of 1000 psia

Cumulative production (Tcf) up to April 2011

Remaining reserve (Tcf)

Recovery %

A 9.7 7.25 2.4782302

4.77 25.51

BC 1.555 1.20 0.6667072

0.53 42.83

Results


Flowing wellhead pressure approach:A sand: For individual well of A sand the reserves at abandonment P/Z of 1000 psia, reaming reserves and recovery factor for each well are in the following well.

Table : GIIP, Reserves, Cumulative production, Remaining Reserve & Recovery

Well name GIIP (bcf) Reserves (bcf) at P/Z of 1000 psia

Cumulative production (bcf) up to April 2011

Remaining reserves (bcf)

Recovery %

T1A 890 685 338.6795 346.3205 38.05

T2A 940 730 325.2039 404.7961 34.60

T3A 710 555 310.2267 244.7733 43.69

T4A 800 610 258.4766 351.5234 32.31T5A 910 710 316.4576 393.5424 34.78

T6A 730 570 251.3580 318.6420 34.43

T7A 790 600 232.0970 367.9030 29.38

T11A 1350 1050 156.2427 893.7573 11.57T12A 325 255 24.3902 230.6098 7.50

T13A 450 345 102.2771 242.7229 22.73

T14A 285 220 72.3942 147.6058 25.40

T15A 395 295 43.2764 251.7236 10.96

T16A 825 635 47.1503 587.8497 5.72∑=7.260 (Tcf)

Results

Figure 5.1: Average gas production & Flowing well head pressure at titas 1 of A Sand.

05001000150020002500300035004000

05

101520253035404550

Mar-69

Nov-70

Jul-72

Mar-74

Nov-75

Jul-77

Mar-79

Nov-80

Jul-82

Mar-84

Nov-85

Jul-87

Mar-89

Nov-90

Jul-92

Mar-94

Nov-95

Jul-97

Mar-99

Nov-00

2-Jul

4-Mar

5-Nov 7-

Jul9-

Mar Flowing well head pressure (psig)Average Gas production MMscfd

Month

Well name T-1AGas MMscfd FWHP Psig

Results


BC Sand:

Using the flowing wellhead pressure approach,

Gas initially in place is 1.6 Tcf.

Reserves at abandonment P/Z of 1000 psia is 1.220Tcf

Cumulative production up to April 2011 is 0.6667072 Tcf.

Remaining reserve is o.55 Tcf

And the recovery factor is 41.67%

Comparison of Results


Table: Comparison of result

Comparison of the results of volumetric & material balance method

Name of the method

GIIP in A Sand(Tcf)

GIIP in BC Sand (Tcf)

Total GIIP (Tcf)

Reserve (Tcf)

Recovery factor (%)

Volumetric 5.68 0.523 6.2065 *4.257 70

Conventional material balance

9.7 1.555 11.255 *8.45 75

Flowing gas material balance

9.43 1.6 11.03 *8.4 76

Name of the method

GIIP in A Sand(Tcf)

GIIP in BC Sand (Tcf)

Total GIIP (Tcf)

Reserve (Tcf)

Recovery factor (%)

Volumetric 5.56 0.522 6.082 *4.257 70

Conventional material balance

9.45 1.550 11.00 *7.700 70

Flowing gas material balance

7.92 1.440 9.360 *5.79 62

Comparison of ResultsPrevious Calculation

Table: Comparison of result


Comparison of Results

• From the estimation of reservoir performance, however the production data analysis shows more accurate result with less data. The other methods shows reliable and comparable results as well.

• By calculating the result the GIIP that we have got using Volumatric method is not much reliable because it shows that in BC Sand the GIIP is 523 Bcf. But up to April 2011 gas produced from BC Sand is 670.80 Bcf.

• So it can be said that recalculation is needed for

volumetric method to estimate GIIP.


Discussion• In case of reserve estimation analysis, first the volumetric

analysis is performed by studying log data. Then the OGIP is found. Using production decline curves (q vs t curve) the production data is analyzed. Flowing material balance is performed based on flowing well head pressure. Conventional material balance is performed based on stabilized shut in pressure at the wells.

• From all the calculations and quantitative analysis, it is observed that different wells shows different nature and different methods shows different amount of gas reserve. Like he total gas in place value of Titas gas field obtained by the volumetric method, flowing well method and conventional method are 6. 2065 Tcf, 11.03 Tcf and 11.255 Tcf respectively.


Problems

But in case of reserve evaluation some problems has been identified this include the following:

• The log data used are not recent. As a result the more accurate results are not found.

• In this research FMB analysis for individuals are also done to show the results would appear if the interference of other wells is not considered.

• The reserved estination by production data analysis is more accurate than volumatric analysis because production data is more updated.

• Dependent upon reliability of the available data


Comment


Comment:

Therefore from the above analysis, it can be expressed

that this research has a few constraints due to different

applications of various methods. Otherwise the results

found here more reliable and can be useful for further

development of Titas gas field. These methods can

also be used for the calculation of other hydrocarbon

zones.

Now I would like to express my deep sense of gratitude to-


Superviser: Dr. M. Farhad Howladar, Assistant Professor, Dept of PME.

Muhammad Imaduddin, Director (PSC) Petrobangla.

All members of the Departmental Academic Committee.

All of my Friends and Family member.

40

…Thank You…


thesis presentation_ final defence

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