Post on 16-Feb-2018
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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…