a intro to pet geomec
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Petroleum GeomechanicsPetroleum Geomechanics
in the Value Chainin the Value Chain
(Introduction to Rock Mechanics inPetroleum Engineering)
Maurice Dusseault
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Petroleum Exploration & ProductionPetroleum Exploration & Production
Geosciences
Geology
Geophysics
Diffusion Sciences (Transport)
Darcy – fluid flow = (Δ p, permeability…)Thermal – heat flow = (ΔT, conductivity…)
Fickian – ionic flow = (ΔC, diffusivity…)
Thermodynamics (energy, phase behavior, etc.)
Geomechanics
Geomechanics is often secondary, but not always!
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Importance of GeomechanicsImportance of Geomechanics
What is GEOMECHANICS?
Geo + mechanics: Mechanics of geological
materials (soils, rocks, fluids in the rocks…)
…deformation-yield-flow behavior of
geomaterials exposed to changes in stresses,pressures, temperatures and chemistry.
…used in exploration, drilling, reservoir eng.,
completion, waste disposal, pipelines…
Geomechanics applications are growing…
Geomechanics knowledge helps reduce risk
Δσ
Δp
ΔT
ΔC
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Stress and PressureStress and Pressure
Petroleum geomechanics
deals with stress & pressure
Stress is a force over an area
Pressure is that part of the
boundary forces supported bythe fluid phase only
Do not confuse the two!
Pressure – p – used for
fluids only.
Fluid can be water, oil, gas…
σa – axial
stress
σr – radial
stress
po
pore
pressure
A
Faa
r
=σ
A
a porous
medium
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Geomechanics and OilGeomechanics and Oil……
Δσ′ - stress changesΔp - pressure changes
ΔC - chemistry changes
ΔT - temperature changes= ΔV - volume changes
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Example: Thermal ContractionExample: Thermal Contraction……
What happen if you
severely cool the
rock? (i.e.: -ΔT)
Shrinking (i.e.: -ΔV)
Loss of confiningstress (i.e.: -Δσ′)
Loss of frictional
strength
The rock slips…
- ΔT =
- ΔV
Δσ′ Δσ′
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Permafrost Stability on a PipelinePermafrost Stability on a Pipeline
Aleyska pipeline
Passive heat transfer in piles to maintain
permafrost frozen, giving good soil stability
Radiator fins
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Surface Heave fromSurface Heave from ΔΔT &T & ΔΔ p p
Surface heaves cannot be explained by Δ
T & Δ
p alone: there must be shear dilationtaking place. Therefore, there are massive changes in the reservoir properties – k, Cc, φ,
Surface heave – Δz –
above a SAGD project
1 k m
320 mm + Δ
z
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Geomechanics ApplicationsGeomechanics Applications
Exploration issues: geology, geophysics, oilemplacement, abnormal pressures, ...
Drilling engineering, borehole stability,casing placement, mud weight window…
Completions engineering, fracturing Reservoir engineering, compaction, fluid
flow, thermal stresses, ...
Process monitoring and optimization… Storage and transportation of products…
Environmental issues, waste disposal, CO2sequestration (see next slide…)
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Carbon Dioxide EmissionsCarbon Dioxide Emissions……
Recovered
CO2 Injection
EOR
CO2 OIL
Sequestration:
EOR, Δp, Δσ′ , ΔC…
Sequestration involves
geomechanics at all
stages…
Carbon emissions (tonnes C/TJ)
Environment Canada
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Geomechanics and the Value ChainGeomechanics and the Value Chain……
Some of geomechanics is problem avoidance
and risk reduction: for example, in drilling…
Stress determination in the earth with depth helps
choose the maximum MW and casing points
Pressure determination and borehole stability anal-
ysis help set the minimum MW and casing points
Geomechanics also saves $ (increased value)
Underbalanced drilling (reduced time and damage) …and helps find resources…
Stress history and pressure valving in basins
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Underbalanced DrillingUnderbalanced Drilling
Drilling Contractor,
Jul/Aug 2003)
1. Underbalanced drilling
requires rock strong enough
to remain open under the
additional forces from fluidinflux.
2. UB drilling is much faster:
time-dependent strength
losses in shale are low.
3. Fluid flux is inward, thus
shale strength is not
affected by mud filtrate.
4. Formation damage reduced
(e.g. capillary blockage),
giving better production.
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Geomechanics and ExplorationGeomechanics and Exploration
State of stress in the earth (drilling, fractures)
Sedimentary basin types and stressdistributions (finding oil accumulations)
Inference of rock properties from seismics and
geophysical logs (reservoir analysis)
Structural and lithostratigraphic issues
Geomechanics of abnormal pressured zones Hydraulic valving of reservoirs (finding gas,
predicting pressures in reservoirs)
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Stresses Above a Domal StructureStresses Above a Domal Structure
Fault identification can help
well planning (avoidance)
σv > σh
Normal faulting
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Drilling GeomechanicsDrilling Geomechanics
Bit-rock interaction
Stresses and pressures around a borehole Physical behavior of shales in vertical and
deviated wells
Borehole stability analysis
Formation damage
Diffusion processes (ΔT, Δ p, ΔC) Salt squeeze and viscous rock behavior
Disposal of drill cuttings by annular injection
ionic specie
concentration
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Horizontal, Slant Wellbore StabilityHorizontal, Slant Wellbore Stability
Verticalstress - σv
Bit-rock
processes
Earth
stresses
Courtesy Statoil
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Completions GeomechanicsCompletions Geomechanics
Mechanical aspects of formation damage
Stresses during and after cementing casing Perforating the cased hole (see next slide)
Hydraulic fracture geomechanicsWhy fractures rise and where they go
Frac-and-pack strategies for completions
Fracturing the horizontal well
Stresses and fracture direction control
Fracturing naturally fractured reservoirs (see
example)
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PerforationPerforation--Damaged ZonesDamaged Zones
Geomechanics issues…
cohesion damage
Introduction of a “flaw”
Focusing of flow paths
cased hole
drilling damage = weakened rock
cement is broken, permeable
perforation damage
f l o w l i n e s
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Reservoir Engineering (I)Reservoir Engineering (I)
What is poroelasticity? Later in the course…
Compaction and subsidence (Maracaibo, Wil-mington, Ekofisk, Ravenna, Groeningen…)
Induced seismicity during conventional
reservoir exploitation (Δ p processes) Geomechanics & thermal EOR processes (ΔT)
Thermal stresses in reservoirs
Changes in rock properties during EOR (dilation)Changes in stresses, induced seismicity
Casing shear problems
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Wilmington. CaliforniaWilmington. California
Bowl shaped Δz
Shear of casings
occurred mainly onthe shoulders of the
subsidence bowl
Few shears in themiddle, where Δz
greatest
Few on flanks
Associated
earthquakes
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Reservoir Engineering (II)Reservoir Engineering (II)
Conventional sand production (avoidance)
Sand management (production enhancement)
Geomechanics of massive sanding as a production mechanism in heavy oils
Geomechanics aspects of methane productionfrom coal seams (see next slide)
Production and injection stress changes
Changes in fractured rock permeabilityChanges in fracture gradient because of
production
Waste disposal by slurry injection
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LateLate--Time Coalbed PermeabilityTime Coalbed Permeability
σ′ - stresspressure - p
‘k’ - apparent
permeability
fracture-dominated stratum
po
ko
σ′ο
1.The CH4 is depleted near thewellbore, - ΔV in coal blocks.
2.Coal fractures open up,increasing permeability.
3.Closure stress drop, helpingfractures remain open
4.
The well improves with time!
affected region
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Surface Heave fromSurface Heave from ΔΔT &T & ΔΔ p p
Surface heaves cannot be explained by ΔT & Δp alone: there must be shear dilation
taking place. Therefore, there are massive changes in the reservoir properties – k, Cc, φ,
Surface heave – Δz –
above a SAGD project
1 k m
320 mm + Δz
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Environmental IssuesEnvironmental Issues
Petroleum development generates wastes…
Drilling wastes, OBM, spent chemicals…
Production wastes, sludges, tank bottoms, produced sand, spills, oily saline produced water,
scale, etc.
Wastes during refining and upgrading of heavy oil
include coke, sulfur (?), ash, sludges, etc.
Waste treatment and disposalChemical or thermal treatment and landfilling…
Injection of liquids, gas scrubbing…
Slurry fracture injection for solids…
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Waste DisposalWaste Disposal……
Slurry injection of sulfur is being considered in Alberta
and Kazakhstan to dispose huge excess S volumes
Is S a waste? Is coke a waste? Do we store them
indefinitely? How do we dispose or treat wastescheaply, with high environmental security?
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Process MonitoringProcess Monitoring
PVT and geochemical data
Well tests and geomechanics inference Deformation monitoring (Δz, Δθ, Δl)
Seismic monitoring (3D, X-hole, VSP) Microseismic monitoring
Electrical monitoring
Integrated reservoir monitoring for process
understanding and management
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©MB
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TimeTime--Lapse SeismicsLapse Seismics
Red areas = large drops in wave amplitude related to steam injection( Δsaturation, fabric dilation - ΔV, stress changes, pressure changes…)
Shell Peace River, horizontal well cyclic steam stimulation
M c G i l l i v r a y P .
M i c r o s e i s m i c a n d T i m e - l a p s e
S e i s m i c M o n i t o r i n g
o f a H e a v y O i l
E x t r a c
t i o n P r o c e s s a t P e a
c e R i v e r , C a n a d a , C
S E G
R e c o r d e r , J a n
u a r y 2 0 0 5 ,
5 - 9
Δ A Δt
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Lessons LearnedLessons Learned……
Geomechanics issues arise in almost all
branches of the oil and gas E&P industry
Petroleum engineers should be well versed ingeomechanics as well as fluid flow
But, this is not as common as it should be Borehole stability, hydraulic fracturing, sand
production, reservoir compaction, etc…, are
among issues dominated by geomechanics Implementing geomechanics into planning
saves money, avoids problems, reduces risk