04a Frac Design Variables (Height) v4 SPE

7/21/2019 04a Frac Design Variables (Height) v4 SPE

1/23

Work Process1. Estimate Stresses and

Pressures

2. Determine Fcd and FOI(Evaluate Various Proppants and

Frac Lengths)

3. Preliminary ProppantSelection

4. Estimate Fracture

Geometry

a) YoungsModulusb) Sand/Shale

5. Fluid LossC and SpurtLoss

6. Fluid Selectiona) Apparent Viscosity (cps)b) Basic Chemistry / Additives

7. Calibrate ModelDiagnosticsa) Fracturing Pressure

b) Temperature/RA Logs

c) Microseismic

8. Final Treatment Pump

Schedule

9. Operations / Perforating


2/23

FRACTURE DESIGN

VARIABLES

H

, E , C ,

K

Ic

-

App

m

, Q, Vor

Building A Basis of Design


3/23

Fracturing PhysicsH, E, C, KIC m, Q, TP

SdSh

Net

AppIc

Net

NetClosure

PP

P

Pf

H

HH

K

E

LQ

H

EP

E

PH

E

PH

w

HwTHC

TQL

m

0

4/1

2

4

4

4

'2'2

)(

3


4/23

Fracture Height (Ho)Questions We Can Answer

Is there a potential for stress differences and thus,confinement ?

Is there a potential for stress differences that could

prevent fracturing the total thickness of the

formation ?

How big might stress differences be ?Depth

PReservoirand Depletion


5/23

Fracture Height (Ho)Questions We Cannot Answer

What is the shale stress ?


6/23

Federal court in Oklahoma City.

Springer formation in Western Oklahoma.

Small company was a co-owner.

Sent a Telex to try and stop large company from fracing well.

The small company and the land owner took the big company to court to sue

for lost reserves.

You are the judge.


7/23

Major Factors

Closure Stress DifferencesFormation Thickness Effects

Fracture Pressure (HO, E, m, KIc-App)

Modulus ContrastsBedding Plane Slip(Probably Only At Shallow Depths)

Rock Ductility

Stress/Fluid Pressure Gradients

Strength (Toughness) Differences


8/23

In Situ Stress Differences

2700 meter Canadian Well

0.7psi/ft with no stress

difference

Fracture was radial

Shallow zone showed 1000

psi difference in stress

Did a severe limited entry

but still did not treat upperzone as noted from Post-

Frac GR tracer


9/23


10/23


11/23

Major Factors


Fracture Pressure (HO, E, , KIc-App)

Modulus Contrasts

Bedding Plane Slip(Probably Only At Shallow Depths)

Rock DuctilityStress/Fluid Pressure Gradients



12/23

Effect of Formation ThicknessPay Zone

203050 100 200300

200

300

500

1,000

2,000

3,000

FractureHeight, H (ft)

,

Q=30bpm

=150cp

C=0.001ft/minXf =700ft

E=2

E=6x10 psi6

E=4x10 psi

6

E=1x10 psi6

F

Net Pressure

for Near PerfectHeight

Confinement


13/23

Effect of Formation ThicknessBoundary Layers


14/23


15/23

Major Factors



Modulus Contrasts

Bedding Plane Slip(Probably Only At Shallow Depths)




16/23

Modulus ContrastsVery Little Effect on Height

E2

E1

E2x

f

H

5 10 2030

1

2

3

E / E21


17/23

Major Factors



Modulus Contrasts

Bedding Plane Slip (Elastic Debonding)(Probably Only At Shallow Depths)




18/23

Bedding Plane SlipOnly At Shallow Depths

5001000150020002500

500

1,000

1,500

2,000

Net OverburdenStress(psi)(Overburden- PorePressure)

FractureStopped

At Interface

FractureCrossedInterface


19/23

Interface Slip/Elastic Debonding

Mineback experiments,

BUT essentially 0

Net Overburden


20/23

Major Factors


Fracture Pressure (HO

, E, m, KIc-App

)

Modulus Contrasts

Bedding Plane Slip (Elastic Debonding)(Probably Only At Shallow Depths)




21/23

Stress/Pressure GradientsOnly Important After Massive Height Growth

Dep

th

Closure Stress

Fluid Pressure Gradient

A FractureWOULD Rather

Grow Up Than

Down.

F t H i ht E ti t


22/23

Fracture Height Estimates,(i.e. Shale-SandEstimates)

Lithology Logs(Bed Thickness)

In Situ Stresses(Pore Pressure, Pore Pressure Variations,

Stress Tests, Acid Breakdown Data)Special Stress Logs(Must Be Calibrated)

Modulus Contrasts

(Sonic Log Data)

Experience + Sound Engineering Judgement


23/23

Fracture Height =

Who do you rule for?

04a Frac Design Variables (Height) v4 SPE

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