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© 2016 BAKER HUGHES INCORPORATED. ALL RIGHTS RESERVED. TERMS AND CONDITIONS OF USE: BY ACCEPTING THIS DOCUMENT, THE RECIPIENT AGREES THAT THE DOCUMENT TOGETHER WITH ALL INFORMATION INCLUDED THEREIN IS THE

CONFIDENTIAL AND PROPRIETARY PROPERTY OF BAKER HUGHES INCORPORATED AND INCLUDES VALUABLE TRADE SECRETS AND/OR PROPRIETARY INFORMATION OF BAKER HUGHES (COLLECTIVELY "INFORMATION"). BAKER HUGHES RETAINS

ALL RIGHTS UNDER COPYRIGHT LAWS AND TRADE SECRET LAWS OF THE UNITED STATES OF AMERICA AND OTHER COUNTRIES. THE RECIPIENT FURTHER AGREES THAT THE DOCUMENT MAY NOT BE DISTRIBUTED, TRANSMITTED, COPIED OR

REPRODUCED IN WHOLE OR IN PART BY ANY MEANS, ELECTRONIC, MECHANICAL, OR OTHERWISE, WITHOUT THE EXPRESS PRIOR WRITTEN CONSENT OF BAKER HUGHES, AND MAY NOT BE USED DIRECTLY OR INDIRECTLY IN ANY WAY DETRIMENTAL

Geomechanics Assessment of Depletion

(and Injection) Induced Changes: Risks of

Reservoir Compaction & Subsidence, Well

Integrity, Fault Reactivation & Earthquakes

Abbas Khaksar (PhD)

Global Geomechanics Advisor

Geoscience and Petroleum Engineering, Baker Hughes Inc.

AOG Conference Perth, West Australia 23 February, 2017

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Definition of Geomechanics

Geomechanics is the study of Earth stresses and mechanical properties of rocks at their current states, their changes and their effects

Present-day geological structures (folds, faults, fractures, etc.) are the consequence of the past stresses which may not be active today

Oilfield operations, and hence behaviour of reservoir and cap rocks, faults, etc. are strongly influenced by the present-day stress state Sv

- Pore pressure

- Rock mechanical properties

- In situ stress orientations &

magnitudes

- Faults and fractures Ge

om

ech

an

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l Mo

de

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Geomechanical modelling is therefore the basis for understanding rock behaviour and developing solutions for drilling, completion, stimulation and exploitation of conventional & unconventional reservoirs: to avoid hazards, increase efficiency and optimize production, safely and economically

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Where and When is Geomechanics Needed in Oil Fields?

-to-abandonment

-to-field applications

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Geomechanical Modeling, Workflow and Input Data

Drilling & Production Data mud weights/ECD, survey, drilling history &

events, XLOT/XLOT, Pp data, DST, production info

Geomechanical Model stress magnitudes & orientation, pore

pressure & rock strength

Core Data Routine &SCAL

UCS, TWCPSD, thin section, SEM, dispersion, chemical

Geolo. Geophys. & Petrophy. Seismic, Tectonic history, sediment., analogs, etc.

Pp Prediction Sanding Prediction

Hydraulic fracturing &

Injection Compaction &

Subsidence

Wellbore Stability Fault seal & Fracture

Permeability and

Seismicity

Well Logs Caliper, Gr, Rhob, Acoustic, image,

NME, dipmeter, MWD/ LWD

Update the model

with new data Stress changes with

depletion & injection

Field Development and Reservoir Management

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Depletion Effect on Stresses Reservoir

Depletion

Str

ess

Ma

gnitu

de

Vertical Stress (Sv)

In the reservoir section, the magnitude of the horizontal stresses reduces as the

reservoir depletes.

For a a laterally long layer-cake

( Sh/ Pp) can be determined from poroelastic equations or field scale numerical

modelling, both require calibration with field data.

1

21, pHh PS

Stress profile of infill wells after depletion.

Sh Pp

Pore Pressure & Stress

Pore Pressure & Stress

Fracking data ( ) showed that stress path factors varies in different locations of the field.

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Potential Depletion Effect on Reservoir and Overburden

After M.B. Dusseault et al. (2001) Casing Shear: Causes, Cases, Cures

Fault reactivation due to Depletion

Reservoir compaction, surface subsidence

compression and shear damage within production interval

shearing at the top of production/injection zones

localized horizontal shear at weak lithology interfaces within the overburden

Depth

Thickness

H

Subsidence

Compaction

Reservoir Diameter

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Casing Damage from Compaction

Example casing deformation patterns from Ekofisk Field (SPE 28091)

~10m compaction, ~3.7m surface subsidence

Shear damage in overburden Buckling damage in reservoir

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Example of Subsidence- Ekofisk, North Sea

Cost estimate: Ekofisk complex in the North

Sea was sinking by approximately 40cm/yr and had reduced the safety air gap of 20m to 16.3m between the platform decks and storm waves. In order to compensate for the

was born with

the platform legs and raising the decks 6m. This was the largest lift and most prestigious project in the world at the time with a total value of £400 million, and for IMH Commissioning Engineers the most challenging and rewarding undertaken at

Example: Ekofisk, North Sea

http://www.conocophillips.no/PublishingImages/Ekofisk_Complex_Press-Photo3.jpg http://subseaworldnews.com/2012/08/15/subsea-7-to-conduct-underwater-operations-on-norwegian-ekofisk-field/ http://www.imh -uk.com/wp-content/uploads/2012/10/Deck-Elevation-Project-for-Ekofisk-Oil-Platform-Field-Subsidence.pdf

Compaction and Subsidence can be predicted and modelled with a reasonable accuracy

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Model Calibration for Subsidence and Compaction

Modelled subsidence Comparison with surface data

Subsidence (surface data)

Onshore, subsidence can be calibrated with surface data (GPS, InSAR

Offshore, regular bathymetric surveys or platform positioning (GPS, InSAR)

Compaction (downhole measurements)

Compaction calibration requires downhole measurement.

CMI - radioactive bullet placed in the formation with regular spacing.

Sureview Wire monitoring - optic fibers clamped on a casing

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Real Time Compaction Monitoring (RTCM)

How it Works:

Thousands of Fiber Brag Grating on a fiber

Each FBG responds individually to strain

Software combines the information and creates a 3D image

Directly measures axial strain, radius of curvature of bend and crushing

Characteristic response differentiates the mode of deformation

Axial compression (compaction) & tension

Bending, Ovalization, Shearing

Figure 8. Unique signatures are seen for a) pure

axial strain, b) bend our buckle, c) and shearing.

a b c

Figure 8. Unique signatures are seen for a) pure

axial strain, b) bend our buckle, c) and shearing.

a b ca b c

Pure Axial

Strain

Bend or

Buckle

Shearing

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8 major reservoirs are constrained with 3 major

faults.

6 individual structural models are available for the

reservoir sections.

R6 has been in water/gas injection for EOR since

1994.

R4 and R5 are planned to be injected for EOR

from 2017.

Zone of interest

*All

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Modelling of Compaction and Subsidence Case Study from South East Asia

Business motivations:

1) Loss of permeability due to pore collapse

2) Platform subsidence

3) Fault permeability after depletion / re-injection

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Simulation Results: Compaction and Subsidence (strain)

Total subsidence

Compaction of individual layers

with depletion and injection