©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Petroleum Geomechanics Petroleum Geomechanics in the Value Chainin the Value Chain
(Introduction to Rock Mechanics in Petroleum Engineering)
Maurice Dusseault
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Petroleum Exploration & ProductionPetroleum Exploration & Production
GeosciencesGeologyGeophysics
Diffusion Sciences (Transport)Darcy – fluid flow = ƒ(Δp, permeability…)Thermal – heat flow = ƒ(ΔT, conductivity…)Fickian – ionic flow = ƒ(ΔC, diffusivity…)
Thermodynamics (energy, phase behavior, etc.)Geomechanics
Geomechanics is often secondary, but not always!
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
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
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Stress and PressureStress and Pressure
Petroleum geomechanics deals with stress & pressureStress is a force over an areaPressure is that part of the boundary forces supported by the fluid phase onlyDo 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
AFa
a
r
=σ
A
a porous medium
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Geomechanics and OilGeomechanics and Oil……
Δσ′ - stress changesΔp - pressure changesΔC - chemistry changesΔT - temperature changes= ΔV - volume changes
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Example: Thermal ContractionExample: Thermal Contraction……
What happen if you severely cool the rock? (i.e.: -ΔT)Shrinking (i.e.: -ΔV)Loss of confining stress (i.e.: -Δσ′)Loss of frictional strengthThe rock slips…
-ΔT = -ΔV
Δσ′ Δσ′
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
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
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Surface Heave from Surface Heave from ΔΔT & T & ΔΔpp
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 km
320 mm +Δz
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Geomechanics ApplicationsGeomechanics Applications
Exploration issues: geology, geophysics, oil emplacement, abnormal pressures, ...Drilling engineering, borehole stability, casing placement, mud weight window…Completions engineering, fracturingReservoir engineering, compaction, fluid flow, thermal stresses, ...Process monitoring and optimization…Storage and transportation of products…Environmental issues, waste disposal, CO2sequestration (see next slide…)
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
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
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
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 pointsPressure 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
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Underbalanced DrillingUnderbalanced Drilling
Drilling Contractor, Jul/Aug 2003)
1. Underbalanced drilling requires rock strong enough to remain open under the additional forces from fluid influx.
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.
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Geomechanics and ExplorationGeomechanics and Exploration
State of stress in the earth (drilling, fractures)Sedimentary basin types and stress distributions (finding oil accumulations)Inference of rock properties from seismics and geophysical logs (reservoir analysis)Structural and lithostratigraphic issues Geomechanics of abnormal pressured zonesHydraulic valving of reservoirs (finding gas, predicting pressures in reservoirs)
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Stresses Above a Domal StructureStresses Above a Domal Structure
Fault identification can help well planning (avoidance)
σv > σh
Normal faulting
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Drilling GeomechanicsDrilling Geomechanics
Bit-rock interactionStresses and pressures around a boreholePhysical behavior of shales in vertical and deviated wellsBorehole stability analysisFormation damage Diffusion processes (ΔT, Δp, ΔC) Salt squeeze and viscous rock behaviorDisposal of drill cuttings by annular injection
ionic specie concentration
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Horizontal, Slant Wellbore StabilityHorizontal, Slant Wellbore Stability
Vertical stress - σv
Bit-rock processes
Earth stresses
Courtesy Statoil
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Completions GeomechanicsCompletions Geomechanics
Mechanical aspects of formation damageStresses during and after cementing casingPerforating the cased hole (see next slide)Hydraulic fracture geomechanics
Why fractures rise and where they goFrac-and-pack strategies for completionsFracturing the horizontal wellStresses and fracture direction controlFracturing naturally fractured reservoirs (see example)
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
PerforationPerforation--Damaged ZonesDamaged Zones
Geomechanics issues…cohesion damageIntroduction of a “flaw”Focusing of flow paths
cased hole
drilling damage = weakened rockcement is broken, permeableperforation damage
flow lines
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Hydraulic Fracture, MicroseismicsHydraulic Fracture, Microseismics
Barnett Shale gas play, Dallas-Ft. Worth region, HF necessaryNaturally fractured shaley reser-voir, low matrix permeabilitySingle or multiple HF fractures??This microseismic-Δt trace shows:
Growth of fracture lengthOpening of “associated” natural fractures in the Barnett reservoirMuch larger drainage area!
Maxwell SC et al. 2003. Fracs tracked using microseismic images. Hart’s E&P, Aug., 58-60.
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
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 (Δp processes) Geomechanics & thermal EOR processes (ΔT)
Thermal stresses in reservoirsChanges in rock properties during EOR (dilation)Changes in stresses, induced seismicityCasing shear problems
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Wilmington. CaliforniaWilmington. California
Bowl shaped ΔzShear of casings occurred mainly on the shoulders of the subsidence bowlFew shears in the middle, where Δz greatestFew on flanksAssociated earthquakes
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Reservoir Engineering (II)Reservoir Engineering (II)
Conventional sand production (avoidance)Sand management (production enhancement)Geomechanics of massive sanding as a production mechanism in heavy oilsGeomechanics aspects of methane production from 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
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
LateLate--Time Coalbed PermeabilityTime Coalbed Permeability
σ′ - stress pressure - p
‘k’ - apparent permeability
fracture-dominated stratum
po
koσ′ο
1.The CH4 is depleted near the wellbore, -ΔV in coal blocks.
2.Coal fractures open up, increasing permeability.
3.Closure stress drop, helping fractures remain open
4.The well improves with time!
affected region
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Reservoir Engineering Reservoir Engineering –– Heavy OilHeavy Oil
In HO unconsolidated sandstones, geomechanics behavior is a first-order factor…
Thermal expansion and shear-induced dilationRecompaction drive in cyclic Δp processes (CSS)Shear of casing because of formation shearIntegrity of overburden sealChanges in k, Cc, φ because of dilation
An understanding of the geomechanics issues involved in thermal EOR helps operations and planning…
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Surface Heave from Surface Heave from ΔΔT & T & ΔΔpp
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 km
320 mm +Δz
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Environmental Issues Environmental 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…
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
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 wastes
cheaply, with high environmental security?
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Process MonitoringProcess Monitoring
PVT and geochemical dataWell tests and geomechanics inferenceDeformation monitoring (Δz, Δθ, Δl)Seismic monitoring (3D, X-hole, VSP)Microseismic monitoringElectrical monitoringIntegrated reservoir monitoring for process understanding and management
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
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
McG
illivr
ay P
. M
icro
seis
mic
and
Tim
e-la
pse
Seis
mic
Mon
itorin
g of
a H
eavy
Oil
Extra
ctio
n Pr
oces
s at
Pea
ce R
iver
, Can
ada,
CSE
G R
ecor
der,
Janu
ary
2005
, 5-9
ΔAΔt
©MBDCI©MBDCI
1-A
Int
ro to
Pet
role
um G
eom
echa
nics
Lessons LearnedLessons Learned……
Geomechanics issues arise in almost all branches of the oil and gas E&P industryPetroleum engineers should be well versed in geomechanics as well as fluid flow
But, this is not as common as it should beBorehole stability, hydraulic fracturing, sand production, reservoir compaction, etc…, are among issues dominated by geomechanicsImplementing geomechanics into planning saves money, avoids problems, reduces risk