Lecture 1 - Final for Posting

Reservoir Geomechanics

In situ stress and rock mechanics applied to reservoir processes ��

Week 1 – Lecture 1 Course Overview

Mark D. Zoback Professor of Geophysics

Stanford|ONLINE gp202.class.stanford.edu

Why is Geomechanics Important?

Drilling and Reservoir Engineering •  Compaction, Compaction Drive, Subsidence, Production-

Induced Faulting Prediction •  Optimizing Drainage of Fractured Reservoirs

•  Hydraulic Propagation in Vertical & Deviated Wells

•  Wellbore Stability During Drilling (mud weights, drilling directions)

•  Completion Engineering (long-term wellbore stability, sand production prediction)

•  Well Placement (Azimuth and Deviation, Sidetracks)

•  Underbalanced Drilling to Formation Damage

Reservoir Geology and Geophysics

•  Optimizing Drainage of Fractured Reservoirs

•  Pore Pressure Prediction

•  Understanding Shear Velocity Anisotropy

•  Fault Seal Integrity

•  Hydrocarbon Migration

•  Reservoir Compartmentalization

Exploitation of Shale Gas/Tight Gas/Tight Oil

•  Properties of Ultra-Low Permeability Formations

•  How Formation Properties Affect Production

•  Optimizing Well Placement

•  Multi-Stage Hydraulic Fracturing

•  Importance of Fractures and Faults on Well Productivity

•  Interpretation of Microseismic Data

•  Simulating Production from Ultra-Low Permeability Formations

Text for Class

Part I – Basic Principles Chapters 1-5

Part II – Measuring Stress Orientation and Magnitude

Chapters 6-9 Part III – Applications

Chapters 10-12

Course Syllabus – Part I - Basic Principles

Week 1 Lecture 1 – Introduction and Course Overview Lecture 2 – Ch. 1 - The Tectonic Stress Field

HW-1 Calculating SV from density logs Week 2 Lecture 3 - Ch. 2 - Pore Pressure at Depth

HW-2 Estimating pore pressure from porosity logs Lecture 4 - Ch. 3 - Basic Constitutive Laws Week 3 Lecture 5 - Ch. 4 - Rock Strength

HW-3 Estimating rock strength from geophysical logs Lecture 6 - Ch. 4 - Fault Friction and Crustal Strength

HW-4 Calculating limits on crustal stress Week 4 Lecture 7 - Ch. 5 - Faults and Fractures

HW-5 Analysis of fractures in image logs Stanford|ONLINE gp202.class.stanford.edu

Course Syllabus – Part II – In Situ Stress

Week 4 Lecture 8 - Ch. 6 - Stress Concentrations Around Vertical Wells Week 5 Lecture 9 - Ch. 7 - Hydraulic Fracturing, Measuring Shmin, Limiting Frac Height and Constraining Shmax

HW-6 Analysis of stress induced wellbore failures Lecture 10 - Ch. 8 - Failure of Deviated Wells Week 6 Lecture 11 - Ch. 9 - State of Stress in Sedimentary Basins

HW-7 Identification of critically-stressed faults

Course Syllabus – Part III - Applications

Week 6 Lecture 12 - Ch. 10 - Wellbore Stability -1 Week 7 Lecture 13 - Ch. 10 - Wellbore Stability – 2 Lecture 14 - Ch. 11 - Critically-Stressed Faults and Flow

HW-8 Development of a geomechanical model Week 8 Lecture 15 - Ch. 11 - Fault Seal and Dynamic Hydrocarbon Migration Lecture 16 - Ch. 12 - Effects of Depletion, Reservoir Stress Paths Week 9 Lecture 17 - Ch. 12 - Compaction of Weak Sands and Shales and Subsidence

Course Syllabus – Additional Topics

Week 9 Lecture 18 – Geomechanics and Shale Gas/Tight Oil Production - 1 Week 10 Lecture 19 – Geomechanics and Shale Gas/Tight Oil Production - 2 Lecture 20 - Geomechanics and Triggered Seismicity

Exploration Appraisal Development Harvest Abandonment

Geomechanical Model

Product ion

Wellbore Stability Pore Pressure Prediction

Sand Production Prediction

Compaction

Depletion

Subsidence Casing Shear

Fault Seal/Fracture Permeability

Fracture Stimulation/ Refrac Coupled Reservoir Simulation

Geomechanics Through the Life of a Field

Components of a Geomechanical Model

Sv – Overburden SHmax – Maximum horizontal

principal stress Shmin – Minimum horizontal

principal stress

Shmin SHmax

Principal Stresses at Depth

UCS Pp Pp – Pore Pressure

UCS – Rock Strength (from logs) Fractures and Faults (from Image

Logs, Seismic, etc.)

Additional Components of a Geomechanical Model

Anderson Classification of Relative Stress Magnitudes

Tectonic regimes are defined in terms of the relationship between the vertical stress (Sv) and two mutually perpendicular horizontal stresses (SHmax and Shmin)

Normal

Strike-slip

Reverse

Map View StereonetCross-section

SHmaxShmin

Sv > SHmax > Shmin

SvNormal

SHmax > Sv > Shmin

SHmax > Shmin > Sv

Strike-Slip

Reverse

SHmaxShmin

Range of Stress Magnitudes at Depth

Hydrostatic Pp

Figure 1.4 a,b,c – pg.13

Variations in Pore Pressure Within Compartments, Each With ~Hydrostatic Gradients

Figure 2.4 – pg.32 Stanford|ONLINE gp202.class.stanford.edu

Range of Stress Magnitudes at Depth

Overpressure at Depth

Figure 1.4 d,e,f – pg.13

Laboratory Testing

Figure 3.2 – pg.58 Stanford|ONLINE gp202.class.stanford.edu

Constitutive Laws

Figure 3.1 a,b – pg.57 Stanford|ONLINE gp202.class.stanford.edu

Figure 3.1 c,d – pg.57

Constitutive Laws

Section 1 •  Compressive Strength •  Strength Criterion •  Strength Anisotropy Section 2 •  Shear Enhanced Compaction •  Strength from Logs, HW 3 Section 3 •  Tensile Strength •  Hydraulic Fracture Propagation •  Vertical Growth of Hydraulic Fractures Stanford|ONLINE gp202.class.stanford.edu

Outline of Lecture

Limits on Stress Magnitudes Hydrostatic P

Sv −Pp

Shmin −Pp

Shmin =Sv −Pp

3.1+Pp

Shmin ≈ 0.6Sv

Critical Shmin

Critical SHmax

SHmax −Pp

Sv −Pp

SHmax = 3.1 Sv −Pp( ) +Pp

SHmax −Pp

Shmin −Pp

SHmax = 3.1 Shmin −Pp( ) +Pp

Normal

Strike-slip

Reverse

Map View StereonetCross-section

SHmaxShmin

Sv > SHmax > Shmin

SvNormal

SHmax > Sv > Shmin

SHmax > Shmin > Sv

Strike-Slip

Reverse

SHmaxShmin

Stress Regimes and Active Fault Systems

Stress Concentration Around a Vertical Well

Compressional and Tensile Wellbore Failure

UBI Well A FMI Well B

Well A

Drilling Induced Tensile Wall Fractures

FMI FMS Stanford|ONLINE gp202.class.stanford.edu

Visund Field Orientations

Regional Stress Field in the Timor Sea

Complex Stress Field in the Elk Hills Field

Horizontal Principal Stress Measurement Methods Stress Orientation

Stress-induced wellbore breakouts (Ch. 6) Stress-induced tensile wall fractures (Ch. 6) Hydraulic fracture orientations (Ch. 6)

Earthquake focal plane mechanisms (Ch. 5) Shear velocity anisotropy (Ch. 8)

Relative Stress Magnitude

Earthquake focal plane mechanisms (Ch. 5) Absolute Stress Magnitude

Hydraulic fracturing/Leak-off tests (Ch. 7) Modeling stress-induced wellbore breakouts (Ch. 7, 8) Modeling stress-induced tensile wall fractures (Ch. 7, 8)

Modeling breakout rotations due to slip on faults (Ch. 7)

Horizontal Principal Stress Measurement Methods Stress Orientation

Stress-induced wellbore breakouts (Ch. 6) Stress-induced tensile wall fractures (Ch. 6) Hydraulic fracture orientations (Ch. 6)

Earthquake focal plane mechanisms (Ch. 5) Shear velocity anisotropy (Ch. 8)

Relative Stress Magnitude

Earthquake focal plane mechanisms (Ch. 5) Absolute Stress Magnitude

Hydraulic fracturing/Leak-off tests (Ch. 7) Modeling stress-induced wellbore breakouts (Ch. 7, 8) Modeling stress-induced tensile wall fractures (Ch. 7, 8)

Modeling breakout rotations due to slip on faults (Ch. 7)

Why do we use these techniques? 1. Model is developed using data from formations of interest 2. Every well that is drilled tests the model 3. They work!

Obtaining a Comprehensive Geomechanical Model

Vertical stress S v z 0 ( ) = ρ g dz 0

∫ Shmin ⇐ LOT, XLOT, minifrac

Least principal stress

SHmax magnitude ⇐ modeling wellbore failures

Max. Horizontal Stress

Pore pressure Pp ⇐ Measure, sonic, seismic

Stress Orientation Orientation of Wellbore failures

Parameter Data

Rock Strength Lab, Logs, Modeling well failure Faults/Bedding

Planes Wellbore Imaging

Wellbore Wall Stresses for Arbitrary Trajectories

Generalized World Stress Map

-35 -35

SHmax incompressionaldomain

SHmax and Shminin strike-slipdomain

Shmin inextensionaldomain

M.L. Zoback (1992) and subsequent papers

~5cm/yr

Critically-Stressed Faults and Fluid Flow

Exploration Success Targeting Critically-Stressed Faults in

Damage Zones

Reservoir Faults &

Damage Zones Hennings et al (2012)

Depletion in Gulf of Mexico Field X

Feb-82

Nov-84

Aug-87

May-90

Jan-93

Oct-95

Jul-98

Apr-01

Jan-04

Depletion in Gulf of Mexico Field X

• Elliptical reservoir at 16300 ft depth with single well at centre • Reservoir dimensions – 6300 x 3150 x 70 ft, grid – 50 x 50 x 1 • Average permeability – 350 md, φinit – 30% • Oil flow, little/no water influx, no injection • IP – 10 MSTB/d, min. BHP - 1000 psi, Econ. Limit – 100 STB/d • Ran for maximum time of 8000 days

Compaction Drive

Simulation Result - Recovery

0 2000 4000 6000 8000 10000

Elastic strain only (Constant compressibility)

Compaction drive

Compaction drive with permeability change

Compaction Drive

National Geographic, October 2004

Land Loss 1932-2050

Land Gain 1932-2050

Oil and gas fields are pervasive

through the region of high rates of

land loss.

Study Area

( ) ( ) ( ) ( )

( ) ( ) ( ) ( )⎪⎩

⎪⎨

Δ−=

Δ−−=

∫∞ −

∞ −

αααν

drJRJepHRCru

( ) ( )∫ Δ=ΔH

m dzzpzCH0

Assuming R>>H, total reduction in reservoir height:

For a circular reservoir, surface displacements are:

Geertsma Model

Study Area: LaFourche Parish

Leeville Subsidence

Palo Duro

Woodford

Avalon

Barnett 24-252 Tcf

Haynesville (Shreveport/Louisiana) 29-39 Tcf

Fayetteville 20 Tcf

Floyd/ Conasauga

Niobrara/Mowry

Cane Creek

Monterey

Michigan Basin

Utica Shale

Horton Bluff Formation

New Albany 86-160 Tcf

Marcellus 225-520 Tcf

Antrim 35-160 Tcf

Lewis/Mancos 97 Tcf

Green River 1.3-2 Trillion Bbl

Gammon

Colorado Group >300 Tcf

Bakken 3.65 Billion Bbl

Montney Deep Basin >250 Tcf

Horn River Basin/ Cordova Embayment >700 Tcf

Eagle Ford 25-100+ Tcfe

OIL SHALE PLAY

GAS SHALE PLAY

✓ ✓

Current Shale Gas/Tight Oil Research Projects

✓ ✓

Eagle Ford Shale Pore Structure

10 µm 500 nm

Shale Permeability is a Million Times Smaller Than Conventional Reservoir

Horizontal Drilling and Multi-Stage Slick-Water Hydraulic Fracturing Induces Microearthquakes (M ~ -1 to M~ -3)

To Create a Permeable Fracture Network

Multi-Stage Hydraulic Fracturing

Dan Moos et al. SPE 145849

Palo Duro

Woodford

Avalon

Barnett 24-252 Tcf

Haynesville (Shreveport/Louisiana) 29-39 Tcf

Fayetteville 20 Tcf

Floyd/ Conasauga

Niobrara/Mowry

Cane Creek

Monterey

Michigan Basin

Utica Shale

Horton Bluff Formation

New Albany 86-160 Tcf

Marcellus 225-520 Tcf

Antrim 35-160 Tcf

Lewis/Mancos 97 Tcf

Green River 1.3-2 Trillion Bbl

Gammon

Colorado Group >300 Tcf

Bakken 3.65 Billion Bbl

Montney Deep Basin >250 Tcf

Horn River Basin/ Cordova Embayment >700 Tcf

Eagle Ford 25-100+ Tcfe

OIL SHALE PLAY

GAS SHALE PLAY

We Need to Dramatically Improve Recovery Factors

Dry Gas ~25% Petroleum Liquids ~ 5% Stanford|ONLINE gp202.class.stanford.edu

Recent Publications Physical properties of shale reservoir rocks

Sone, H and Zoback, M.D. (2013), Mechanical properties of shale-gas reservoir rocks—Part 1: Static and dynamic elastic properties and anisotropy, Geophysics, v. 78, no. 5, D381-D392, 10.1190/GEO2013-0050.1

Sone, H and Zoback, M.D. (2013), Mechanical properties of shale-gas reservoir rocks—Part 2: Ductile creep, brittle strength, and their relation to the elastic modulus, Geophysics, v. 78, no. 5, D393-D402, 10.1190/GEO2013-0051.1

Slowly slipping faults during hydraulic fracturing

Das, I. and M.D Zoback (2013), Long-period, long-duration seismic events during hydraulic stimulation of shale and tight gas reservoirs — Part 1: Waveform characteristics, Geophysics, v.78, no.6, p. KS107–KS118.

Das, I., and M.D Zoback (2013), Long-period long-duration seismic events during hydraulic stimulation of shale and tight gas reservoirs — Part 2: Location and mechanisms, Journal of Geophysics, , v.78, no.6, p. KS97–KS105.

Recent Publications Why slow slip occurs

Kohli, A. H. and M.D. Zoback (2013), Frictional properties of shale reservoir rocks, Journal of Geophysical Research, Solid Earth, v. 118, 1-17, doi: 10.1002/jgrb. 50346 Zoback, M.D., A. Kohli, I. Das and M. McClure, The importance of slow slip on faults during hydraulic fracturing of a shale gas reservoirs, SPE 155476, SPE Americas Unconventional Resources Conference held in Pittsburgh, PA, USA 5-7 June, 2012

Fluid transport/adsorption in nanoscale pores

Heller, R., J. Vermylen and M.D. Zoback (2013), Experimental Investigation of Matrix Permeability of Gas Shales, AAPG Bull., in press. Heller, R. and Zoback, M.D. (2013), Adsorption of Methane and Carbon Dioxide on Gas Shale and Pure Mineral Samples, The Jour. of Unconventional Oil and Gas Res., in review.

Recent Publications . Viscoplasticity in clay-rich reservoirs

Sone, H. and M.D. Zoback (2013), Viscoplastic Deformation of Shale Gas Reservoir Rocks and Its Long-Term Effects on the In-Situ State of Stress, Intl. Jour. Rock Mech., in review. Sone, H and M.D. Zoback (2013), Viscous Relaxation Model for Predicting Least Principal Stress Magnitudes in Sedimentary Rocks, Jour. Petrol. Sci. Eng., in review.

Discrete Fracture Network Modeling in Unconventional Reservoirs

Johri, M. and M.D. Zoback, M.D. (2013), The Evolution of Stimulated Reservoir Volume During Hydraulic Stimulation of Shale Gas Formations, URTec 1575434, Unconventional Resources Technology Conference in Denver, CO, U.S.A., 12-14 August 2013

Case Studies Yang, Y. and Zoback, M.D., The Role of Preexisting Fractures and Faults During Multi-Stage Hydraulic Fracturing in the Bakken Formation, Interpretation, in press

An Increase in Intraplate Seismicity

Prague, OK* Nov. 2011 M 5.7

Prague, OK 3 M5+ Eqs Nov., 2011

Zoback (2012)

An Increase in Intraplate Seismicity

Prague, OK* Nov. 2011 M 5.7

Prague, OK 3 M5+ Eqs Nov., 2011

Ellsworth (2013)

Managing Triggered Seismicity

EARTH April, 2012

Hurd and Zoback (2012)

Earthquakes Spreading Out Along an Active Fault

Horton (2012) Stanford|ONLINE gp202.class.stanford.edu

- Avoid Injection into Potentially Active Faults - Limit Injection Rates (Pressure) Increases - Monitor Seismicity (As Appropriate) - Assess Risk - Be Prepared to Abandon Some Injection Wells

Seismicity Triggered by Injection

Guy Arkansas Earthquake Swarm

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