©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