a intro to pet geomec

8/9/2019 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

©MB

©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

a intro to pet geomec

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