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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
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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FRACTURE DESIGN
VARIABLES
H
, E , C ,
K
Ic
-
App
m
, Q, Vor
Building A Basis of Design
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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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
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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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
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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Fracture Height (Ho)Questions We Cannot Answer
What is the shale stress ?
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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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.
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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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
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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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
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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7/21/2019 04a Frac Design Variables (Height) v4 SPE
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7/21/2019 04a Frac Design Variables (Height) v4 SPE
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Major Factors
Closure Stress DifferencesFormation Thickness Effects
Fracture Pressure (HO, E, , KIc-App)
Modulus Contrasts
Bedding Plane Slip(Probably Only At Shallow Depths)
Rock DuctilityStress/Fluid Pressure Gradients
Strength (Toughness) Differences
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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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
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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Effect of Formation ThicknessBoundary Layers
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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7/21/2019 04a Frac Design Variables (Height) v4 SPE
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Major Factors
Closure Stress DifferencesFormation Thickness Effects
Fracture Pressure (HO, E, m, KIc-App)
Modulus Contrasts
Bedding Plane Slip(Probably Only At Shallow Depths)
Rock DuctilityStress/Fluid Pressure Gradients
Strength (Toughness) Differences
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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Modulus ContrastsVery Little Effect on Height
E2
E1
E2x
f
H
5 10 2030
1
2
3
E / E21
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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Major Factors
Closure Stress DifferencesFormation Thickness Effects
Fracture Pressure (HO, E, m, KIc-App)
Modulus Contrasts
Bedding Plane Slip (Elastic Debonding)(Probably Only At Shallow Depths)
Rock DuctilityStress/Fluid Pressure Gradients
Strength (Toughness) Differences
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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Bedding Plane SlipOnly At Shallow Depths
5001000150020002500
500
1,000
1,500
2,000
Net OverburdenStress(psi)(Overburden- PorePressure)
FractureStopped
At Interface
FractureCrossedInterface
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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Interface Slip/Elastic Debonding
Mineback experiments,
BUT essentially 0
Net Overburden
7/21/2019 04a Frac Design Variables (Height) v4 SPE
20/23
Major Factors
Closure Stress DifferencesFormation Thickness Effects
Fracture Pressure (HO
, E, m, KIc-App
)
Modulus Contrasts
Bedding Plane Slip (Elastic Debonding)(Probably Only At Shallow Depths)
Rock DuctilityStress/Fluid Pressure Gradients
Strength (Toughness) Differences
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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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
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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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
7/21/2019 04a Frac Design Variables (Height) v4 SPE
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Fracture Height =
Who do you rule for?