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Petroleum GeomechanicsPetroleum Geomechanics

Examples where Geomechanics Knowledge is Vital

Maurice Dusseault

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ePetroleum Geomechanics AreasPetroleum Geomechanics Areas……

Borehole stability (+ chemistry, diffusion, wellbore hydraulics…)Hydraulic fracturing (+ fracture and porous media flow of fluids & slurries, filtration…)Reservoir compaction (+ reservoir mechanics, geological history, mineralogy…)Sand production (+ capillarity, hydrodynamic forces…)Thermally-induced casing shear (+ thermo-dynamics, fluid flow…)

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eCoupled ProblemsCoupled Problems……

All these are coupled problems! Solve a fluid flow

problem to get a general pressure distribution, {p}

Pressures change stress so use {p} in a stress-strain (σ’-ε) problem

Δσ’ generates ΔV, so we have to put this back into

the pressure solution

ReservoirSimulator for Δp & ΔT

Geomechanics Simulator for Δσ'-ε solution

Diffusion mechanics

Continuum mechanics

Measurements for verification and model calibration

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eThree Chosen Case HistoriesThree Chosen Case Histories

Borehole Stability at Cusiana (Colombia)$35,000,000 per hole before changes$12-15,000,000 per hole after changes

Compaction at Ekofisk-Valhall (North Sea)Massive surface subsidencePlatform rebuilding as necessary, casing shear

Casing Shear in Cyclic Steam (Canada)Massive shear stresses from thermal stressesHorizontal wells help solve the problem

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eColombia TectonicsColombia Tectonics……

COLOMBIA

Venezuela

Panama

Ecuador

Peru

Brasil

http://geology.about.com/library/bl/maps/blcolombiamap.htm http://geology.com/world/colombia-satellite-image.shtml

Cusiana

→ Massive Borehole Stability

Problems

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eThe General Stability ProblemThe General Stability Problem……

Cusiana Field, 4270 m, discovered in 1989In foothills just east of last major Andes rangeLithology: alternating sand-shale sequenceTectonics: active faulting, overthrust belt, very high in situ shear stress at depth (near failure)10 months drilling time, lost 20-30% of wells that were spudded, >10% of time spent on cleaning holes, expensive mud, stuck pipe, sidetracks, distorted casings, and so on$35,000,000 per well in 1990-1992 period…

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eThe Geomechanics ProblemThe Geomechanics Problem

Very high stresses in situRelatively weak rocks (mechanical weakness)Fissile shales dipping at up to 30-40°Inclined joints and fissures that can slip if the MW is too high, creating hole constrictionsThese issues led to the problems observed:

Massive breakouts, sloughing, hole enlargementOil-based muds not effective (ie: natural fractures)Stuck pipe from joint displacementsHole cleaning problems, tripping problems…

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eStressesStresses……

Ref

: Mar

kley

ME

, Las

t N, M

endo

za S

, Muj

ica

S. C

ase

Stu

dies

of

Cas

ing

Def

orm

atio

n…, I

AD

C/S

PE

645

61.

Dal

las

TX 2

002.

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eBorehole StabilityBorehole Stability……

Borehole management involves not only stresses, rock strength, MW, mud type…!It also depends on hydraulics & chemistry:

Pumping strategy and cleaning capabilitiesGel strength, viscosity, mud density, filtrate chem.BHA design, ECD, even tripping policy

Rock mechanics Hydraulics

Chemistry

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HOW DO WE REDUCE HOW DO WE REDUCE ECONOMIC RISKS IN ECONOMIC RISKS IN

DRILLING AT CUSIANA?DRILLING AT CUSIANA?

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eMassive Subsidence Massive Subsidence -- EkofiskEkofisk

Huge reservoir, over 300 m thick in centerHigh porosity (high-φ) Chalk (see next slide)Oil production causes:

Drawdown of reservoir pressure – pIncrease in effective stress – σ′Collapse of high-φ Chalk to a lower porosityMassive reservoir compaction (> 9 m at present)Seafloor subsidence (>8 m at present)And - good reservoir drive energy!

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eCoccolithicCoccolithic Structure of ChalkStructure of Chalk

Hju

lerM

L. 2

007.

Dia

gene

sis

of U

pper

Cre

tace

ous

onsh

ore

and

offs

hore

ch

alk

from

the

Nor

th S

ea a

rea.

PhD

The

sis,

Inst

itute

of E

nviro

nmen

tal a

nd

Res

ourc

es, T

echn

ical

Uni

vers

ity o

f Den

mar

k, 7

0 p.

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eHollow Hollow CoccolithsCoccoliths, Little Cement, Little Cement

Ris

nes,

R.,

Mad

land

, M.V

., H

ole,

M. &

Kw

abia

h, N

.K.,

2005

. Wat

er w

eake

ning

of

cha

lk –

Mec

hani

cal e

ffect

s of

wat

er-g

lyco

l mix

ture

s. J

ourn

al o

f Pet

role

um

Scie

nce

and

Engi

neer

ing,

48,

21-

36.

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eEkofiskEkofisk……

10 km

Reservoir structure

Subsidence bowl

saltPorosity, φ ≈50% in this

zone

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eValhallValhall DispositionDisposition

From: Zoback MD, Zinke JC. Production-induced Normal Faulting in the Valhall and Ekofisk Oil Fields. Pure Appl.

Geophys. 159 (2002) 403-420

Ekofisk and Valhall are similar Chalk reservoirs, formed because of deep-seated salt doming creating an anticline.EKOFISK

Geography

VALHALL

A

A′

Deep salt ridge

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eMassive Reservoir Compaction Massive Reservoir Compaction

Seafloor subsidenceLeads to wave risks for platformsCasing shearing (some wells redrilledseveral times)Wonderful drive sustaining process!

1973

1984

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eCasing Shear at Casing Shear at EkofiskEkofisk……

Source: EPOKE, Phillips Petroleum, No 7, 1999

6262000

6263000

6264000

6265000

6266000

6267000

6268000

6269000

6270000

6271000

510000 511000 512000 513000 514000 515000 516000E-W Coordinates

N-S

Coo

rdin

ates

Overburden

Reservoir

Distribution of overburden shear damage and producing interval compaction damage

at Ekofisk(SPE 71695)

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eRock Mechanics ImplicationsRock Mechanics Implications

During development (1969-1975), engineers failed to predict massive subsidenceWhen noted in 1981-83, maximum subsidence was greatly underestimated (~6-7 m)Also, engineers failed for many years to understand the water-weakening phenomenonSome consequences:

Platform jacking by 6.3 m in 1988-89Complete platform redevelopment in 1999-2002Far greater OOIP and production rate

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eProductionProduction--Injection HistoryInjection History

Start water injection

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eButBut……

Ekofisk taught us a great deal…The need for very careful rock testing under in situ conditions without altering the materialLinks between rock behavior, capillarity, chemistry and fluid flow (Δp) are important.Coupled modeling is needed for realistic predictions in reservoir geomechanicsMeasurements are always importantRisks can be reduced by careful geomechanicsThere will always be some surprises!

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HOW DO WE MANAGE HOW DO WE MANAGE ECONOMIC RISKS BECAUSE ECONOMIC RISKS BECAUSE

OF SUBSIDENCE AT EKOFISK?OF SUBSIDENCE AT EKOFISK?

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eImperial Oil Cold LakeImperial Oil Cold Lake

50 km

Imperial Oil Cold Lake Property

Edmonton

Calgary

Saskatoon

Regina

Alberta Saskatchewan

Lloydminster

Alb

erta

Ene

rgy

Util

ities

Boa

rd D

ocum

ents

ht

tp://

ww

w.e

ub.c

a/do

cs/d

ocum

ents

/dec

isio

ns/1

999/

d99-

22.p

df

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eCasing Shear in Thermal ProjectsCasing Shear in Thermal Projects

High temperature (To ~ 25°C, Ti ~ 225-325°C)Large degree of thermal expansion of the sand reservoir that is convectively (flow) heatedThis also leads to thermal dilation of the sand, giving a large volume increase (1-3%)Overlying shale does not increase in volume (conductive heating is slow, no dilation)This means a great deal of shear stress is concentrated at the sand-shale interfaceCased wellbores cannot withstand this (shear)

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mod. Stancliffe & van der Kooij, AAPG 2001

+285 mm

+200

-210

+260

+130 mm

-165km

+100 Vertical displacements

(mm)over 86 days

subsidenceheave

Imperial Oil Imperial Oil –– Cold LakeCold Lake

Mega-RowCSS

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eThermallyThermally--Induced ShearInduced Shear……

thermal front,ΔV - expansion

displacementpattern

Shale: impermeable, stiff

Sandstone, permeable, softer

ovalization and collapsetendencies near interfaces

(large stress concentrations)

dogleg over an interval

Note: casing experiences substantial distortional loading far in advance of the arrival of the thermal front. Largest shear stresses probably coincide with the thermal front.

Shale: impermeable, stiff

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eThermal Compaction as WellThermal Compaction as Well……

Lost Hills, California Δz Interferogram

Subsidence Induced Fissure

Courtesy: Michael S. Bruno

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HOW DO WE MITIGATE HOW DO WE MITIGATE ECONOMIC IMPACTS OF ECONOMIC IMPACTS OF

CASING SHEAR?CASING SHEAR?

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eExerciseExercise…… Three separate groupsThree separate groups……

Each group develop a list of strategies for managing the risk associated with…

Group 1: Borehole instability, high stress areaGroup 2: Massive subsidence, offshore fieldGroup 3: Casing shear, thermal project

Write down your choices, we will present them and discuss them briefly…

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eCusianaCusiana and Borehole Stabilityand Borehole Stability

Choice of inclined well trajectory to penetrate shales at 90° (±15°), in the optimum directionAdditives to plug induced shear fractures and delay hole sloughing behaviorCareful mud controlChange casing pointsBetter hole cleaning & hydraulics to cope with the large sloughingEtc.

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eThe Risk Minimization LoopThe Risk Minimization Loop……

Sm

irnov

NY,

Lam

R, R

au II

I WE

. 20

03.

Pro

cess

of i

nteg

ratin

g G

eom

echa

nics

w

ith w

ell d

esig

n an

d dr

illing

ope

ratio

n. ,

AAD

E 20

03 N

atio

nal T

echn

olog

y C

onfe

renc

e “P

ract

ical

Sol

utio

ns fo

r Dril

ling

Cha

lleng

es”,

Hou

ston

, Tex

as, P

aper

A

AD

E-0

3-N

TCE

-28.

Mechanical

Earth Model

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eNow at Now at EkofiskEkofisk……

Water injection is sustaining the reservoir pressure. This reduces but does not eliminate the reservoir compaction. Wells are drilled and equipped with more compliant casing so that more shear distortion can occur without shearing or breachingMeasurements: seafloor gauges, logging, etc.Better modeling and therefore predictionsHowever, Ekofisk made us humble! We did not predict its behavior in advance!

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eHandling Casing ShearHandling Casing Shear

Mitigation strategies include:Adjusting well trajectories (avoidance)Adjusting injection/production strategiesModifying hole size and cementing practiceChanging casing grade (D/t ratio)Changing inner completion designAccept damage risk and adjust economicsAccept risk, design for easier re-drills, repairs…

Geomechanics analysis helps quantify risk…

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e Well PerformanceComparison Tool

CommonDesign AnalysisDatabase

AnalyticalAnalysisTool

Simple DecisionAnalysis Tool

ProprietaryReservoir Analysis

ProprietaryWell Damage Analysis

ProprietaryDecisionAnalysis

Well PerformanceComparison Tool

Well PerformanceComparison

Tool

CommonDesign AnalysisDatabase

CommonDesign AnalysisDatabase

AnalyticalAnalysis

Tool

AnalyticalAnalysis

Tool

Simple DecisionAnalysis Tool

Simple Decision

Analysis Tool

ProprietaryReservoir Analysis

ProprietaryReservoir Analysis

Estimate

Reservoir Deformation

Well Deformation

Limits

ProprietaryWell Damage Analysis

ProprietaryWell Damage

Analysis

ProprietaryDecisionAnalysis

ProprietaryDecisionAnalysis

Optimum Well Design

Risk Mitigation in Casing ShearRisk Mitigation in Casing Shear

Courtesy: Michael S. Bruno

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eShell Oil Canada Shell Oil Canada –– Peace RiverPeace River

ref. Nickle’s New Technology Magazine, Jan-Feb 2005

Surfaceuplift / tilt

data

reservoir inversion gridwith 50x50m grid cells

Multi-lateralCSS

Less well shear because of well

trajectories!

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eLessons LearnedLessons Learned……

In many instances, geomechanics knowledge is vital to oil and gas developmentBorehole stability (Cusiana example)Subsidence (Ekofisk example)Casing shear (Oil sands Cold Lake example)And many others…These are “coupled” problems (combined stress-flow problems – Δp, ΔT, Δσ)Implementing geomechanics into planning reduces risk, avoids problems, lowers costs…