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Geomechanic for Hydraulic Fracturing in Unconventional Reservoirs 1 Raul German Rachid Production Stimulation Engineer Schlumberger Argentina Bolivia Chile 04-Jul-11
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Page 1: Geomechanicfor Hydraulic Fracturing in Unconventional ... · Geomechanicfor Hydraulic Fracturing in Unconventional Reservoirs 1 ... Reservoir & Source Rock Trap ... maximize benefit

Geomechanic for Hydraulic Fracturing

in Unconventional Reservoirs

1

Raul German Rachid

Production Stimulation Engineer

Schlumberger

Argentina Bolivia Chile

04-Jul-11

Page 2: Geomechanicfor Hydraulic Fracturing in Unconventional ... · Geomechanicfor Hydraulic Fracturing in Unconventional Reservoirs 1 ... Reservoir & Source Rock Trap ... maximize benefit

Agenda

2

� Introduction to Unconventional Reservoirs

� Consequences of Heterogeneity and Lamination

� Stress Profile Modeling in Anisotropic Media

� Horizontal Wells

� Fracture Geometry Simulation

� Conclusions

04-Jul-11

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Introduction to

Unconventional

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Unconventional

Reservoirs

04-Jul-11

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The Industry Challenge

� Orders of magnitude reductions in permrequire orders of magnitude increase inreservoir contact

� Efficiency key to economic successConventional ReservoirsConventional ReservoirsConventional ReservoirsConventional Reservoirs

Small volumes that are

easy to develop

Unconventional Unconventional Unconventional Unconventional

1md +1md +1md +1md +

0.01 md

4S

chlu

mb

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Unconventional Unconventional Unconventional Unconventional

Large volumes

difficult to

develop

0.001 md

0.00001 md

04-Jul-11

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Shales are unconventional reservoirs S

chlu

mb

erger P

ub

lic

504-Jul-11

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Shale Gas Introduction

What are they?– Organic-rich shale– Source rocks

– Adsorbed and free gas

– Very low permeability

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licCommon traits of gas shale reservoirs– Abundant gas (20 to 400 BCF/mi2)

– Large developments (economies of scale)– Large and numerous hydraulic stimulations

– Long well life (60-year reserves common)

04-Jul-11

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Trap, Reservoir & Source Rock

Trap/Seal

Trap

Conventional Unconventional

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04-Jul-11

7

Reservoir

Source

Reservoir

Source

Rock is too tight to let go of Hydrocarbon

so source rock acts as the trap

and the Reservoir

Hydrocarbon leaves source and settles

in the reservoir because it cannot

pass the trap

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Heterogeneous Rock at Fine Scale

Matrix

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SPE 131772

Kerogen

04-Jul-11

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Sal

t

Ara

b-D

Car

bona

te

Jona

h La

nce

Fm

. (T

ight

GA

S)

Cem

CR

ET

E

Org

anic

Sha

le

Bric

k

Ber

ea S

and

Shale in Perspective: Permeability

9S

chlu

mb

erger P

ub

lic

1000 10100 1.0 0.1 0.001 0.0001 0.00001 1e-060.01

Bric

k

Ber

ea S

and

md

Unconventional

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Earth Scale

SEM Scale

Mechanical Properties for ShalesThe Consequence of Laminations

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Core Scale

Thin Section Scale

SEM Scale

Log Scale04-Jul-11

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Unconventional Shale Gas Reservoirs

�Hydraulic fracture containment is often either unknown or perceived as uncertain.

�Traditional stress modeling in shale gas reservoirs has

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�Traditional stress modeling in shale gas reservoirs has lead to inefficient fracturing or unexpected height growth.

�However by considering anisotropic rock properties……

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Heterogeneity

A heterogeneous material is one consisting of

dissimilar or diverse constituents

Homogenous Heterogeneous Heterogeneous

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Anisotropy

Isotropic Anisotropic Anisotropic

Anisotropy is defined as the variation of a property

with the direction in which it is measured.

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Evaluate using core, logs and seismic04-Jul-11

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What is a Transversely Isotropic medium?

Isotropic mediaIsotropic mediaIsotropic mediaIsotropic media

Same property in the 3 principal directions of space

Transverse isotropicTransverse isotropicTransverse isotropicTransverse isotropic

Property is the same in 2 principal directions:

- TIV same property in horizontal plane

- TIH same property in vertical plane

X

Y

Z

X

Y

Z

Isotropic

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- TIH same property in vertical plane

OrthotropicOrthotropicOrthotropicOrthotropic

Property varies in 3 directions

XY

Z

X

Y

Z

TIV

TIH

Orthotropic04-Jul-11

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Stress Modeling of Shales

Jaeger and Cook – Fundamentals of Rock Mechanics (1979)

This is the case of a sedimentary rock with z-axis perpendicular to the bedding,

and the increase of the number of elastic constants from two for the isotropic

case to five is formidable. There is no great difficulty in handling many

mathematical problems involving such materials, cf. Hearmon (1961), Savin

(1961); the difficulty for practical purposes is in obtaining and using realistic

values of the elastic constants.

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values of the elastic constants.

( )pVph Pv

vP ασασ −

−=−

1

( )pVh

V

V

hph P

v

v

E

EP ασασ −

−=−

1

Isotropic

TransverseIsotropic

04-Jul-11

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Traditional Stress Modeling: Isotropy� σ vertical

Stress Profile

Shale

Sandstone

Isotropy assumes that:

Horizontal = Vertical

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σ h

σ vσ p

( ) tectonicspvph +−−

=− σσυ

υσσ1

Shale

Sandstone All conventional sonic tools !!

04-Jul-11

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Stress Profiles in Anisotropic Rock

Where:

� E = Young’s Modulus Vertical

� v = Poisson’s Ratio Vertical

σ vertical

E, vE’, v’

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� v = Poisson’s Ratio Vertical

� E’ = Young’s Modulus Horizontal

� v’ = Poisson’s Ratio Horizontal

( ) tectonicsh

v

Ev

Ehpvph +−

−=− σσ

υυσσ

1

Laminated Shale which is the

reservoir & source rock

04-Jul-11

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Vertically Anisotropic Formation – Impact on Frac Height

Isotropic Stress Anisotropic Stress Sonic Scanner

Leads to more accurate mechanical properties in laminated shales

18

properties in laminated shales

04-Jul-11

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Staging the

Stimulation

Anisotropic Stress

Profile

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Isotropic Stress

Profile

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Comparison of Isotropic and Anisotropic Models

Low stress predicted in shales using conventional earth model in high clay volume rocks

MineralogyGR

Stress

Gradients

Higher stress predicted in shales

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Higher stress predicted in shales using anisotropic earth model in high clay volume rocks

Measured stresses via in-situ stress testing

04-Jul-11

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Impact of Anisotropic Stress Profile

4300

4400

4500

4600

4700

4800

TV

D -

ft

Frac Half Length Propped Frac Half Length4300

4400

4500

4600

4700

4800

TV

D -

ft

Frac Half Length Propped Frac Half Length

Isotropic Stress Profile Fracture Geometry Anisotropic Stress Profile Fracture Geometry

Shale Reservoir Shale

Reservoir

21S

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mb

erger P

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lic

4900

5000

51003500 3600 3700 3800 3900 4000 4100 4200

Stress - psi

-0.2 -0.1 0.0 0.1 0.2

Width at Wellbore - in @118.0 min

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Fracture Half Length - ft @118.0 min

4900

5000

51003000 3500 4000 4500

Stress - psi

-0.10 -0.05 0.00 0.05 0.10

Width at Wellbore - in @119.0 min

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Fracture Half Length - ft @119.0 min

Hydraulic fracture contained within the organic shale

Hydraulic fracture grows above the organic shale

Best barriers for organic shales are conventional, high clay volume inorganic shales

Fractures that grow out of zone will result in poor production regardless of the Reservoir Quality

04-Jul-11

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Proppant Concentration

0.0 PPA 2.0 PPA 4.0 PPA 6.0 PPA 8.0 PPA

Fracture WidthFrac#1 MD = 13495.85ft

Lithology and StressSat. and Young's Modulus

Well

Depth

(TV

D) (ft)

13100

13200

13300

13400

13500

13600

Impact of Stress model on hydraulic fracture Isotropic Vs Anisotropic assumption

22S

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mb

erger P

ub

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> 10.0 PPA

Length (ft)

0 100 200 300 400 500 600 700

Width (in)

-2.00 0 2.00

Stress (psi)

8000.0 10000.0 12000.0 14000.013700

Young's Mod. (psi)

4.0x1066.0x1068.0x1061.0x1071.2x107

Proppant Concentration

0.0 PPA 2.0 PPA 4.0 PPA 6.0 PPA 8.0 PPA

> 10.0 PPA

Length (ft)

0 500 1000 1500 2000

Fracture WidthFrac#1 MD = 13487.00ft

Width (in)

-2.00 0 2.00

Lithology and Stress

Stress (psi)

10000.0 12000.0 14000.0 16000.0

Sat. and Young's Modulus

We

ll D

ep

th (

TV

D)

(ft)

13100

13200

13300

13400

13500

13600

13700

13800

Young's Mod. (psi)

4.0x106 6.0x106 8.0x106 1.0x107

04-Jul-11

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Anisotropy and Fracture Containment

( )pVph Pv

vP ασασ −

−=−

1

( )Vh PvE

P ασασ −=−

Isotropic Blue (v)

Anisotropic Red (Eh, EV, νh, νV)

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( )pVh

V

V

hph P

v

v

E

EP ασασ −

−=−

1

Leads to more accurate mechanical properties inlaminated formations

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`

24S

chlu

mb

erger P

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04-Jul-11

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Frac Breakdown

Pressure

4000

5000

6000

7000

Pre

ssu

re [p

si]

40

50

60

70

Slu

rry Rate [b

pm

]P

rop C

on

x 10 [PP

Ax10]

Koone 4-34H Stage 2

0

1000

2000

3000

4000

5000

6000

7000

8000

0 15 30 45 60 75 90 105 120

Time [min]

Pre

ssu

re [

psi

]

0

10

20

30

40

50

60

70

80

Slu

rry Rate [b

pm

]P

rop

Co

n x 10 [P

PA

x10]

Lithology σHmin

25S

chlu

mb

erger P

ub

lic

0

1000

2000

3000

0 15 30 45 60 75 90 105 120

Time [min]

Pre

ssu

re [p

si]

0

10

20

30

Slu

rry Rate [b

pm

]P

rop C

on

x 10 [PP

Ax10]

04-Jul-11

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Unconventional

Reservoir

Fracturing

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Fracturing

Evaluation04-Jul-11

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Hydraulic Fracturing Direction

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Hydraulic Fracturing Direction

SH

S

ShSH

Sh

28

� Low stress anisotropy

� Lower seismic anisotropy

� Wide fracture fairway

� High stress anisotropy

� Higher seismic

anisotropy

� Narrow fracture fairway

SH

Sh

SH

Sh

04-Jul-11

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Fracture Geometry Information from Horizontal Image LogsVariable Induced Fractures Infers Variable Stress

Transverse Fractures Only:

σσσσHHHH >> σσσσhhhh

No Fractures:

High High High High σσσσ’’’’

Long & Trans Fractures:

Low Low Low Low σσσσ‘ & ‘ & ‘ & ‘ & σσσσHHHH ~ σσσσh h h h

Long, Narrow Fracture FairwayLong, Narrow Fracture FairwayLong, Narrow Fracture FairwayLong, Narrow Fracture FairwayWide Fracture FairwayWide Fracture FairwayWide Fracture FairwayWide Fracture FairwayNo FracturesNo FracturesNo FracturesNo Fractures

29

04-Jul-11

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SPE-90051 (HW)

30S

chlu

mb

erger P

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SRV or ESV04-Jul-11

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SPE-90051

31S

chlu

mb

erger P

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lic

04-Jul-11

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SPE-90051

32S

chlu

mb

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Effective use of the fracturing fluid

Volume optimization using the fracture acoustic volume for make real time decisions.

04-Jul-11

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geophonesgeophonesgeophonesgeophones

Effective Stimulated VolumeEffective Stimulated VolumeEffective Stimulated VolumeEffective Stimulated Volume

(ESV) density based algorithm(ESV) density based algorithm(ESV) density based algorithm(ESV) density based algorithm

StimMAP* LIVE – Quantifying

Contact Volume

33S

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A Tool to make informed decisionsA Tool to make informed decisionsA Tool to make informed decisionsA Tool to make informed decisions

Event HistogramEvent HistogramEvent HistogramEvent Histogram

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Hydraulic fracture mapping for evaluation

4150D

epth

(ft

)Microseismic Measurements

with prop-placement model

34S

chlu

mb

erger P

ub

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4850

-500 -250 0 250 500Along Fracture Length (ft)

Dep

th (

ft)

4850

SPE 38575 ( DOE-GRI MWX data )

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Slickwater Fluids

– More ft2/$– Wider Fracture “Fairways”

Geled fluids

Fracturing Fluid Selection

35S

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mb

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Geled fluids

– Frac Initiation

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Horizontal

Wells

36S

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mb

erger P

ub

licWells

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Fracture Treatments – Increase Surface Area & Flow

37S

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SurfaceSurface

Wellbore azimuth 90°

Which direction to drill?

Where to land?

Fracture height growth?

Fracture network width?

Fracture conductivity?

Transverse Aplication:

Place Multiple Fracutes

Hydraulic Fractures In Horizontal Wellbores

38S

chlu

mb

erger P

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lic

Vertical StressWellbore azimuth 0

Longitudinal fractures

Reservoir

Minimum horizontal stress

Vertical Stress

Maximum horizontal stress

Wellbore azimuth 90°Transverse fractures

04-Jul-11

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Bedding– Lamination → Complexity

Quartz Rich Shales� Isotropic Behavior

Drilling/Stimulation Efficiency

Lateral Placement

39S

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mb

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� Expanding Clays

� Oil Based Muds

� Borehole Breakout

Closure Stress

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Induced Stress due to a Horizontal Hole in σσσσh Direction

Drilling Process can induce Tensile Stress

Potential Initiation of Tensile Fractures

Longitudinal Fracture

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Borehole

In-Situ Stress Field

Induced Stress Field

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Factors Affecting Fracture GeometryFactors Affecting Fracture GeometryFactors Affecting Fracture GeometryFactors Affecting Fracture Geometry

Weijer 1994 – Fracture

initiate longitudinal when

OH drilled ┴ to σmax, then is

reoriented to transverse .

The effect of induced stress concentration

created by removing a cylinder of supporting

rock is known as “Hoop Stress”.

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Microseismic Data and Fracture Orientation

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SPE 11056243

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04-Jul-11

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Stage 1Stage 1Stage 1Stage 1 Stage 2Stage 2Stage 2Stage 2 Stage 3Stage 3Stage 3Stage 3 Stage 4Stage 4Stage 4Stage 4

σmax avg = .77.77.77.77

σmin ISIPISIPISIPISIP = .70.70.70.70

σM- σm = .07.07.07.07

σmax avg = .74.74.74.74

σmin ISIPISIPISIPISIP = .64.64.64.64

σM- σm = .10.10.10.10

σmax avg = .69.69.69.69

σmin ISIPISIPISIPISIP = .65.65.65.65

σM- σm = .04.04.04.04

σmax avg = .65.65.65.65

σmin ISIPISIPISIPISIP = .62.62.62.62

σM- σm =.03.03.03.03

SPE 110562S

chlu

mb

erger P

ub

lic

High High High High Stress Stress Stress Stress

AnisotropyAnisotropyAnisotropyAnisotropy

Low Low Low Low Stress Stress Stress Stress

AnisotropyAnisotropyAnisotropyAnisotropy

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Stage 1Stage 1Stage 1Stage 1

Stage 2Stage 2Stage 2Stage 2

Stage 3Stage 3Stage 3Stage 3

Stage 4Stage 4Stage 4Stage 4

σM- σm = .07.07.07.07

σM- σm = .10.10.10.10

σM- σm = .04.04.04.04

σM- σm =.03.03.03.03

∆ P = P = P = P = ----191191191191

∆ P = 249P = 249P = 249P = 249

∆ P = 564P = 564P = 564P = 564

∆ P = 1109P = 1109P = 1109P = 1109

SPE 110562S

chlu

mb

erger P

ub

lic

σM- σm = .10.10.10.10 σM- σm =.03.03.03.03

Stage 2 Stage 3

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Hydraulic

Fracturing

46S

chlu

mb

erger P

ub

lic

Fracturing

Simulation

04-Jul-11

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Fracture geometry modelingDifferences between pseudo 3-D and planar 3-D

47S

chlu

mb

erger P

ub

lic

Propagation and fluid flow are 1-D

Assumes fracture length >> height (plane-strain assumption)

Propagation and fluid flow are 2-D

No assumption/restriction on the aspect ratio (length vs height)

Only constraint – fracture stays within one plane (no bending or turning)

Planar 3Planar 3Planar 3Planar 3Planar 3Planar 3Planar 3Planar 3--------D models are more accurate in layered reservoirs than pseudo 3D models are more accurate in layered reservoirs than pseudo 3D models are more accurate in layered reservoirs than pseudo 3D models are more accurate in layered reservoirs than pseudo 3D models are more accurate in layered reservoirs than pseudo 3D models are more accurate in layered reservoirs than pseudo 3D models are more accurate in layered reservoirs than pseudo 3D models are more accurate in layered reservoirs than pseudo 3--------D, which will D, which will D, which will D, which will D, which will D, which will D, which will D, which will

maximize benefit from petrophysical and maximize benefit from petrophysical and maximize benefit from petrophysical and maximize benefit from petrophysical and maximize benefit from petrophysical and maximize benefit from petrophysical and maximize benefit from petrophysical and maximize benefit from petrophysical and geomechanicalgeomechanicalgeomechanicalgeomechanicalgeomechanicalgeomechanicalgeomechanicalgeomechanical datadatadatadatadatadatadatadata04-Jul-11

Page 48: Geomechanicfor Hydraulic Fracturing in Unconventional ... · Geomechanicfor Hydraulic Fracturing in Unconventional Reservoirs 1 ... Reservoir & Source Rock Trap ... maximize benefit

What is it?– Multi-stage stimulation design and evaluation software for conventional and

unconventional markets

– Integrated in the overall oil field services’ multi-disciplinary solutions;

…petrophysics, G&G, geomechanics, reservoir engineering

How does it work?– Implemented as a Plug-in for Petrel

Unconventional Reservoir Simulator (Mangrove*)48

– Implemented as a Plug-in for Petrel

What is the value?� Differentiate through technical solution rooted in reservoir

characterization (measurements and interpretation),

enabling reservoir centric stimulation design for specific

environments

� Reorient for the global shift to unconventional reservoirs

04-Jul-11

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Multi-staging Advisors�Tight Gas Sandstone & Pilot Shale (Vertical)– 100 separate stacked sands over 3000 ft gross

– Differential depletion

– Starting point AutoFRAC (Denver)

� Shale (Laterals)

– Laterals through heterogeneous rock

– Ultra low permeability

49

Source: www.eandp.info

– Naturally Fractured

Completion challenges

– Consistent model

– Tedious process (2 days – 2 weeks)

Improved Efficiency, Consistency & Knowledge DisseminationImproved Efficiency, Consistency & Knowledge DisseminationImproved Efficiency, Consistency & Knowledge DisseminationImproved Efficiency, Consistency & Knowledge Dissemination

04-Jul-11

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50

04-Jul-11

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HF-NF Interaction (Crossing Criterion)

NF Arrest /

slippage

NF dilation

HF propagating

along NF

HF

51

Crossing

Fissure opening after

crossing

NF staying

closed

04-Jul-11

Page 52: Geomechanicfor Hydraulic Fracturing in Unconventional ... · Geomechanicfor Hydraulic Fracturing in Unconventional Reservoirs 1 ... Reservoir & Source Rock Trap ... maximize benefit

Example of UFM Results with micro-seismic data

52

04-Jul-11

Page 53: Geomechanicfor Hydraulic Fracturing in Unconventional ... · Geomechanicfor Hydraulic Fracturing in Unconventional Reservoirs 1 ... Reservoir & Source Rock Trap ... maximize benefit

Integrating Reservoir & Completion Quality

30000

40000

50000

3 M

on

th

BO

E

� 33% increase in 3 month average cumulative BOE on

new wells. Save $300k in frac costs

� New wells used Reservoir Quality and Completion

Quality to optimize completions.

Effective Porosity

Spectroscopy Volumes

Examine Reservoir and Completion Quality.

Recommend stages with optimal

properties. Variable

53

0

10000

20000

30000

Pre Optimization (6 Wells) Post Optimization (3 Wells)

3 M

on

th

BO

E

Perforations

Shale Stress Index

Poisson’s Ratio

Stress

with optimal properties. Variable number and lengths.

Recommend specific perforation location

− Combined logs and core measurements for the reservoir and completion quality assessment.

− Reservoir Quality technology routine: Triple Combo-Spectroscopy (PEX-ECS/ EcoScope), Di-Electric Scanner, NMR

− Completion Quality technology routine: Borehole Images (FMI, RAB, LWD Density), Sonic Scanner/Mangrove*

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Conclusion & Summary

54

� Unconventional Reservoirs require special consideration related to the heterogeneity.

� Conventional Isotropic stress models can lead to erroneous evaluations.

� Geomechanical Models are becoming more important in the � Geomechanical Models are becoming more important in the process of the Reservoir completion.

� It’s not just about technology, it’s about integrating appropriate technology.

04-Jul-11

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