Coupled Reservoir GeomechanicsModeling for Optimal Field Management

Chee Phuat Tan

Chee Phuat Tan Asia Geomechanics Advisor

Kuala Lumpur, Malaysia

Presentation Objectives

� Introduce geomechanics of reservoir depletion/ injection, compaction/heave/overburden movement, slip on fractures/plane of weakness and fault movement

� Describe effects of mechanisms on reservoir

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Describe effects of mechanisms on reservoir behaviour and performance

� Describe coupled reservoir geomechanicsmodeling workflow

� Illustrate consequences of mechanisms and development of solutions through field examples

Why Do We Need Geomechanics?

Model the effects of depletion:

- identify when best to shoot next monitor survey

- maximize the value of your 4D seismic.

Comparing the base and monitor surveys

- identify the fluid and rock property changes

- more accurate ‘picture’ for decision makingSubsidenceSubsidence

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Effects & Consequences of

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Effects & Consequences of Reservoir Depletion & Injection

Effects of Reservoir Depletion

Pp

σV

σh

Depletion

σV = constant

Pp-∆pp

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Depletion

σV = constant

σh - ∆ σh Pp-∆pp

Region of reduced σhσv

Permeable horizon

Cap rock

σh

New σh

Injection and Loss of Fracture Containment

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Pressurized zone

Potentialfracturing

Compaction-Induced Well Integrity Problems

Any stretch inoverburden

causesextension in casing etc.

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Compacting reservoir

Worst at crest

Shear & localplastic

deformationEuler

buckling

Slip on Fractures and Planes of Weakness

With Depletion (and Compaction and Stress Transfer)

High σhregion

(low angle shear)

Highτ

regionSlip planes

in overburden

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Flanks Shoulders Crest Shoulders Flanks

Reservoir compaction

Damagedcement

Ductileinterval

Cased, cemented w ellbore

Hard interval

Collapsedcasing

LmstMarl

Anhydrite

Natural Fracture ConductivityUnder shear and normal deformationF

ract

ure

aper

ture

a

Fra

ctur

e co

nduc

tivity

k

Fracture dilatingunder shear (i.e. critical stress concept)

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k = ƒ(σ′, a)

Effective normal stress σ′

Fra

ctur

e ap

ertu

re a

Fra

ctur

e co

nduc

tivity

k

Fracture closingunder shear

Changing effectivenormal stress σ′

Fault Re-activation Due to Depletion/Injection

σ′n = σn - p

τ

Production

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Lateral stress increase- Overburden due to production

- Reservoir due to injection

High p area

σH > σv

Lateral stress reduction- Reservoir due to production- Overburden due to injectionNormal faulting mechanism

Thrust faulting mechanismSlip can occur at interfaces

or planes of weakness

Thrust

σ2

σ3

σ1

Change in Optimum Perforation Orientation with Depletion

Safe drawdown

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σ1

σ2

σ3

Strike-slipσ2

σ3

σ1

90o Phasing

0o Phasing

Coupled Reservoir

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Coupled Reservoir Geomechanics Modeling

Porosity correlations�

Manual correlations�

Log data �

Coupled Modeller

Fault surface�

Seismic horizons�

Strength data correlations �

Static Model

Dynamic Model

Coupled Modelling Workflow

Completion Integrity �

1-D MEM

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Coupled ModellerDynamic Model

13

Embedded

Dynamic Model

∆∆∆∆P, ∆∆∆∆T

PVT Tables∆∆∆∆K, ∆φ∆φ∆φ∆φ

Geomechanics

Model

Coupling4-D�

Micro-seismic �

Completions �Sector Model �Fault stability�

Toolkits

Integrity �

Step 1 – Development of Embedded Model� Add grid cells to dynamic model to eliminate

boundary condition effects

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Step 1 – Development of Embedded Model (Cont’d)

� Add embedding grid cells to over, under and side-burdens

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Step 1 – Development of Embedded Model (Cont’d)

� Incorporate faults and fractures

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Step 2 – Development of GeomechanicalProperty Model

� Use static model kriging tools to populate rock mechanical properties...

Neural Networks utility

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Step 3 – Establishment of Initial Stress Conditions

� Boundary conditions...

– Use stress profiles from 1D MEMs as initial boundary

conditions for geomechanical model

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Faults

Step 3 – Establishment of Initial Stress Conditions (Cont’d)

� Determine 3-D stress distribution

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Fractures & Faults

Step 4 – Running of Coupled Simulation

Reservoir Simulation Model

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Geomechanical Model

• User defined steps, or... automated step detection

Application of Post-Processed Output

1-Plan well...

3-Predict well events......Wellbore Stability

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2-Extract properties...

Application of Post-Processed Output (Cont’d)

Well-02

Fault Re-activation

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Well-01

Final compaction

Casing

Stress state along

Cement

Application of Post-Processed Output (Cont’d)Completion Integrity

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Stress state along well trajectory

Well location –Unstructured grid Details around

the well

Field Examples

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Field Examples

Lack of BHP Increase from InjectionReservoir Simulation

Without GeomechanicsMeasured

(Field Data)Reservoir Simulation With Geomechanics

Pre

ssur

e

1000

1500

2000

2500

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• Client expected to see large pressure increase from injection

• Instead small pressure rises and falls from injection were observed

Time

15 years

Top reservoir

Fault and Fracture Behaviour With Production

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• 4-D response of faults and fractures

• Effective drainage area delineation

• Well placement relative to permeability direction/magnitude

• Well design (optimum drain hole)

Depletion-induced Fracture Strain

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Seismic Inverted StrainPredicted Strain

Reservoir Compaction with ProductionGeomechanics Prediction 4-D Seismic Inversion

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• Compaction determined by two independent methods ⇒ difference of ~5 cm

• Prediction helped in development planning & seismic inversion confirmed prediction

Prediction of Completion Failure

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Excessive shear strains along well path

Successfully predicted wellbore integrity problems in formation where not previously expected

Coupled Production Prediction

0

50000

100000

150000

200000

250000

300000

350000

400000

450000

0 5 10 15

Time(Year)

FG

PT

(M

SC

F*E

3)

Coupled-case 2

Coupled-case 1

No Permeabilityupdating

Permeability updating

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

0 5 10 15

Time (year)

FW

PT

(S

TB

^10

E3)

Coupled-case 2

Coupled-case 1

Permeability updating

No Permeabilityupdating

Field water production totalField gas production total

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Time(Year)

Field Pressure History

0

1000

2000

3000

4000

5000

6000

0 5 10 15

Time (year)

FP

R (

PS

IA)

Coupled-case 2

Coupled-case 1

No Permeabilityupdating

Permeability updating

Field pressure history• Reservoir performance/recovery

factor

• Water handling/disposal and facilities design

• Injection and pressure maintenance

4000

5000

6000

7000

Field data

No history match

Example well - WBHP (psia)

History Matching Via Geomechanics

� Two fracture sets were implemented

� Different fracture strike, spacing and

conductivity

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0

1000

2000

3000

0 1 2 3 4 5 6 7

No history matchGeomechanics

Time (year)

Hydraulic Fracture Containment with Injection

Scenario 1 Scenario 2

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• Scenario 1 proposed by client

• Scenario 2 recommended based on results from coupled reservoir geomechanics modeling

Presentation Summary

� Reservoir depletion/injection can impact on reservoir behaviour and performance

– Compaction/heave/overburden movement

– Slip on fractures and planes of weakness

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– Fault movement

� Development of solutions to optimise field management

– Coupled reservoir geomechanics modeling

REMEMBER !!!

Chee Phuat Tan THANK YOU