LPS Seminar- Cased Hole Petrophysics

Utilising multi detector pulsed neutron technologies to understand

behind pipe saturations in Rumaila, Iraq.

Oliver Grimston

Outline

• Rumaila context: location and delivering production

• Nuclear Modelling to interpretation workflow

• The Field Trial: Well XX and Well YY

• Tool Response

• Zubair and Mishrif Petrophysical Interpretation

• Summary

Rumaila location and production history

• Super-giant oil field in SE Iraq

• Stacked pay (clastic & carbonate)

• >80 billion barrels initially in

place

• Low relief N-S anticline ~75 km

long

• Discovered 1953

• Production startup 1955

• Peaky profile from geopolitics

• Rumaila Operating Organization (ROO)

formed in 2010

• BP (lead), CNPC and BOC

North

Rumaila

South

Rumaila

Flank

dips <5°

‘Saddle’~75 km

~15 km

Delivering Production

• Few nuclear logging technologies applied prior 2010

• Previously open hole logging- gamma ray, resistivity sufficient to detect OWC in

clean sands

• Recently multi-detector pulsed neutron (MDPN) introduced for fresh water

detection

• Large field size & multiple reservoirs = high complexity, variable wellbore

conditions & different tool designs

• To assure standardization robust workflows are needed

• Robust saturation model resulted in +20mbbls produced year to date

Ra

teR

ate

Add

perf

WSO

Interpretation Workflow

Well bore

schematic casing

size, thickness…

Borehole

fluid- Gradio,

pressure…

PVT Model

Lithology

Properties-

XRD..

BP Nuclear Simulation Log QC/QA

inc.

uncertainty

analysis

Wellsite

witnessing-

Checking

Spectra

Acquired

MDPN log

data

Interpretation and error propagation

So/Sw; Sg/Sw

Simulate tool response

Uncertainty of So, Sg and Sw

Phases saturation interpretation

Constra

ining

the

model

BP Nuclear modelling Platform

Logging data quality control

Petrophysical Interpretation

Reservoir

description data/

uncertainty

So Sg & Sw

Check

against Res

Model Sat

• An independent and

consistent set of results for all

approved vendors

• BP IP controlled technology at

the forefront of technology

The Field Trial

Well XX

Mishrif

Zubair

Well YY

Objectives

• Investigate saturation response of formation fluids for similar

nuclear attributes with different MDPN instruments

• Assess the measurements sensitivity and saturation uncertainty

• Six wells selected to test the MDPN responses for:

• Well bore design: Observation/Producer Wells

• Wellbore conditions: Flowing & Shut-in

• Formation characteristics: Clastics/Carbonates,

High/Low quality facies

• Two wells (XX and YY) were chosen for this paper

Well XX and Well YY

20 in; 94 lb/ft;

K-133

13 3/8 in; 54.5

lb/ft; L-80

9 5/8 in; 47 lb/ft;

L-80

7 in; 29 lb/ft;

L-80

Well XX Well YY

Perforated

Well and Logging

• Borehole size- 8.5”

• Casing- 7” (29lbm/ft, L-80)

• Logging speed- 2.5-3ft/min

• 3 repeat passes

Well Condition

• Well XX- Borehole Fluid- Oil/Water- 80/20 (240kppm)

• Well YY- Borehole Fluid- Brine- (50kppm)

Formation Fluids

• Well XX- Connate water- ~240kppm NaCL eq.

• Well YY- Connate water- ~210kppm NaCL eq.

• Well XX & YY- Injection water- ~2kppm

• Oil –PVT report

• Reservoir Pressure & Temperature

Formation Lithology

• Well XX- Quartz sandstone (> 90%) with kaolinite clays

• Well YY- Limestone (> 90%) with dolomite & chert

Photos from the field

Tool Response Sensitivities

Mean Mean Standard Deviation

of 3 CO passes

Uncertaint

y (su)

Vendor A 1.14 0.009 12.9

Vendor B 0.62 0.004 8.2

Mean Mean Standard Deviation

of 3 CO passes

Uncertaint

y (su)

Vendor A 1.05 0.011 12.8

Vendor B 0.52 0.004 7.7

Relative sensitivity comparison- response was normalized at origin point for comparison

purpose

Well YY (PHIT > 0.20, the averaged porosity (PHIT) is 0.224)

Well XX (PHIT>0.19, the averaged porosity (PHIT) is 0.22)

Well XX Well YY

• Pre-job models were built to understand

tool response sensitivity in the

carbonate and clastic formations

• Green & blue lines represents tool

response of oil and water saturated

(Vendor A continuous, B dotted).

• Final saturation uncertainty is controlled

by tool response sensitivity and

uncertainty of the actual measurements

• Tool A is ~1/3 more sensitive to oil than

tool B

• Tool B is less uncertain than tool A

Zubair Petrophysical Interpretation

TOPS

AB

D

F

HK

L

MN

C

• Vendor A and B show equivalent sigma and

CO saturations, oxygen activation and

chlorine yield response.

• AB and F/H sands show injection sweep in

amalgamated channel sands

• CO saturation shows oil bearing D sands;

providing wellwork opportunity

• LMN sands – both Sigma and CO indicate

saline aquifer sweep

• Oxygen activation shows water inflow

(arrows) affecting CO response from

heterogeneous wellbore fluids

Understanding Zubair’s Shale Response

Oil sands CO

response

Shale CO

response

Modelled fan chart (oil/water lines) of shale

(dotted) and sand (continuous) for Well XX

• CO reading high, consistent over shale zones suggesting

shale affects CO measurement

• Rumaila is unique - quartz matrix (> 90%) but kaolinite

dominant shale matrix

• Kaolinite clay contains large percentage of aluminium

• Similar cross section & high energy gamma ray may spread

into carbon window

• Result - Similar CO response for shale and oil bearing sands;

highlighting the importance of nuclear modelling

Element Inelastic C.S. @ 14

MeV (barns)

Al 0.4330

C 0.4207

Mishrif Petrophysical Interpretation

• Vendor A and B show equivalent sigma

and CO saturations and yields response.

• Mhf1 fresh water response (arrow)-

↑ sigma saturation, ↓ Chorine yield &

↓ CO saturation.

• Integrating NMR with cased hole

saturation is vital where the OH model

struggles with cherty rock type (arrow)

• At <15% porosity, the CO ratio is highly

uncertain (>30%) and reduces tool’s

dynamic response (arrow)

• Chlorine yield, oxygen activation and

sigma are qualitative curves helping to

monitor small CO saturation changes

• Two MDPN tools were trialled in the carbonate (Mishrif) and clastic (Zubair)

formations and both tools showed comparable saturation response and uncertainty.

• While MDPN tools share same physics, the instrumentation and characterization is

tool specific.

• Thus using in-house workflows to apply nuclear models to simulate tool response in

well conditions provides robust saturation extraction.

• Zubair CO response is similar in oil bearing sands and shale because of the

uniqueness of the kaolinite rich clay

• Carbonates are more challenging and the CO struggles in <15% porosity with

uncertainty above 30%

• Selection of MDPN tools has business value:

• Creates competition on the market

• Provides job specific choice

Summary

Questions

?