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Distinguished Lecturer Online (DLO)
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Society of Petroleum Engineers
Distinguished Lecturer Program
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Effects Of Complex Reservoir Geometries AndCompletion Practices On Production Analysis In Tight
Gas Reservoirs
Stuart A. CoxMarathon Oil Company
Society of Petroleum Engineers
Distinguished Lecturer Programwww.spe.org/dl
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Outline
Introduce production analysis
Reservoir geometries
-Synthetic cases
- Field examples
Completion parameters
-Synthetic cases
- Field examples
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Purpose
Address the following question:
When performing production analysis,can complex reservoir geometries andcompletion practices cause linear flow,limited fracture half lengths and limited
drainage areas to be predicted?
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Conditions
Reservoir geometriesStress dependent permeability
Radial composite
Two-layer system
Completion parametersHydraulic fracture clean-up and damage
Liquid loading
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Production Analysis
Rate, time, pressure analysis
Long term pressure drawdown test
Type-curve matching technique
Major Assumptions- Single-phase fluid
- Constant reservoir / completion properties
- Volumetric production
- Bottomhole pressure known
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Applications ofProduction Analysis
Determine effective drainage volume
Estimate drainage area
Estimate reserves / productive life
Identify infill drilling potential
Estimate reservoir flow capacity
Evaluate completion performance
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0.1
1
10
100
0.0001 0.001 0.01 0.1 1 10 100
tDA
PwD
Infinite Conductivity Fracture
Kh = 3.27 md-ftXf = 200 ft
Boundary Dominated
Uniform Flow
Boundary Dominated
Linear Flow
Infinite Acting Flow
Example of Reservoir Flow Geometryon Diagnostic Type Curve
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0.1
1
10
100
0.0001 0.001 0.01 0.1 1 10 100
tDA
PwDor
PwD'
Actual PwD
Actual PwD'
Analytical PwD
Analytical PwD'
Boundary Dominated
Flow
East Texas Example 2 to 1 Rectangular Boundary at 1,017 Days
Kh = 3.3 md-ft
Inifite Acting
Pseudo Radial Flow
Uniform Flux Fracture
Xf = 380'
Field Example of Flow Characteristics
East Texas Example First 90 Days
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0.1
1
10
100
0.0001 0.001 0.01 0.1 1 10 100
tDA
PwDor
PwD'
Actual PwD
Actual PwD'
Analytical PwD
Analytical PwD'
Boundary Dominated
Flow
East Texas Example 2 to 1 Rectangular Boundary at 1,017 Days
Kh = 3.3 md-ft
Inifite Acting
Pseudo Radial Flow
Uniform Flux Fracture
Xf = 380'
Field Example of Flow Characteristics
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Base Simulation Cases
Uniform 40 acres Model Parameters
Formation top, ft 10,000
Initial reservoir p ressure, psi 5 ,00 0
Net pay, ft 40
Gas specific gravity 0.65
Effective Gas Perm. md 0.05
Fracture half -length, ft 200
Fracture Conductivity, md-ft 75
Simulation Controls
Flowing tubing pressure 350 psia
Production time 2 years
Single layer model
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Base Case Radial Flow
Results match simulation
Average pressure 2,630 psi after 2 years
0.01
0.1
1
10
100
0.0001 0.001 0.01 0.1 1 10 100
tDA
PwDorPwD'
Actual PwD
Actual PwD'
Analytical PwD
Analytical PwD'
InfiniteConductivityFracturein1to 1RectangularBoundaryat2 years
Match Simulation
Kh =2.0md-ft, 2.0md-ftX
f=165ft, 165ft
Area= 40Acres, 40Acres
Pressure, Psia
400 5000
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Stress Dependent Permeability
Matrix Natural Fracture
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Stress Dependent Permeability
Reduced flow capacity
Reduction in reservoir andcompletion flow capacity
Flowing pressure 450 psi0.001
0.01
0.1
1
10
0 1000 2000 3000 4000 5000 6000 7000
Net Stress, Psi
PermeabilityMultiplier
Change in Net Stress, psi
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Natural FractureParameters
Fracture spacing 30 ft
Flow capacity 2.0 md-ft
- Matrix = 0.005 md
- Natural fracture = 0.045 md
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Type Curve Match
0.01
0.1
1
10
100
0.0001 0.001 0.01 0.1 1 10 100
tDA
PwDor
PwD'
ActualPwD
ActualPwD'
Analytical PwD
Analytical PwD'
InfiniteConductivity Fracture in3 to1 Rectangular Boundaryat 2years
Match
Kh = 0.68md-ftXf = 165f t
Area= 23Acres
Reduced flow capacity
Linear flow
Limited drainage area
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Pressure Profile After Two Years
No Stress dependent Permeability Stress dependent Permeability
False depletion stem draining ~ 20 Acres
Linear flow
PA after 16 years resulted in a 40 acre
400 5000
Pressure, Psia
400 5000
Pressure, Psia
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Field ExampleStress Dependant Permeability
Carbonate ~ 10,000 ft
Flow capacity Natural fractured
Completion Horizontal
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Depletion stem
Field ExampleProduction Analysis Results
Rate & Pressure HistoryLog-Log Plot
Limited Reservoir
Flow capacity 13.6 md-ft
Effective length 520 ft
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Pressure Build Modeling
1E-3 0.01 0.1 1 10 1001
10
100
Log-Log plot: p-p@dt=0 and derivative [psi] vs dt [hr]
Log-Log Plot
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Actual Pressure Build UpLog-Log Plot
100 Hour Test
Stimulated well performance
No Boundaries
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Actual Pressure Build UpPressure Match
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Radial Composite
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Radial Composite
Two regions considered- Inner region 5 acres, 2 md-ft
- Outer region 35 acres, 0.02 md-ft
Results- Reduced effective drainage area
- PA match shows linear flow
- Long-term complex transient behavior
- PA after 25 years results show 40 acres
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Type Curve Match
Linear flow with limited drainage area
0.01
0.1
1
10
100
0.0001 0.001 0.01 0.1 1 10 100
tDA
PwDor
PwD'
Actual PwD
Actual PwD'
Analytical PwD
Analytical PwD'
Infinite Conductivity Fracture in 3 to 1 Rectangular Boundaryat 2 years
Case 3Kh = 2.0 md-ft
Xf = 165 ft
Area= 7 Acres
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Pressure Profile After Two Years
Blue area is the 5 acre higher flow capacity area
Radial shape reflected in the model
400 5000
Pressure, Psia
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Hydraulic Fracture Clean-up
Initial fracture conductivity set at 2 md-ft
60 day clean-up to a final fracture conductivity of 75 md-ft
Result show short effective length
0.01
0.1
1
10
100
0.0001 0.001 0.01 0.1 1 10 100
tDA
PwDor
PwD'
Actual PwD
Actual PwD'
Analytical PwD
Analytical PwD'
InfiniteConductivityFracture in 1 to 1 Rectangular Boundaryat 2 years
Match Simulation
Kh = 2.0 md-ft, 2.0 md-ft
Xf = 37 ft, 165ft
Area= 40 Acres, 40 Acres
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0.01
0.1
1
10
100
0.0001 0.001 0.01 0.1 1 10 100
tDA
PwDorPwD'
Actual PwD
Actual PwD'
Analytical PwD
Analytical PwD'
InfiniteConductivity Fracturein 2.2to 1Rectangular Boundaryat 2years
Match Simulation
Kh = 1.8md-ft, 2.0 md-ft
Xf = 181ft, 165ft
Area= 17Acres, 40Acres
Fracture Conductivity Reducing
Fracture conductivity reduced by 1%
each day for the two years
False depletion stem and linear flow
400 5000
Pressure, Psia
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Liquid Loading Whats The Problem?
Additional back pressure on formation?
Poor estimate of actual bottomhole
pressure from surface data?
Imbibition of water into the formation while
the well is flowing and static?
Will the well improve i f unloaded?
Do loaded wells result in a false depletionstem and reservoir shape?
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Wyoming Gas Well
0
500
1000
1500
2000
7/28/2001 12/10/2002 4/23/2004 9/5/2005 1/18/2007
MCFD/FTP/CP
0
25
50
75
100
BWPD/BOPD
MCFD
Unloading Rate,MCFD
BOPD
BWPD
Wyoming Field Example
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Imbibition Under Flowing Conditions
8 ft
Water dP
Gas dP
Exit Pressure
4 ft
MeteredGas Rate
Water Pump
55 galDrum
Laboratory work by Stim-Lab
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Liquid Loading
Standing liquid promotes near-well damage throughspontaneous imbibition.
In field applications it is common to see both linear flow andfalse depletion stems
Pressure profile from the model confirms the false depletion
0.1
1
10
100
1000
0.0001 0.001 0.01 0.1 1 10 100
tDA
PwDor
PwD'x0.1
Actual PwD
Actual PwD'
Analytical PwD
Analytical PwD'
Infinite ConductivityFracture in2.8to 1 Rectangular Boundaryat 2years
Match SimulationKh = 18 md-ft, 20 md-ft
Xf = 45ft, 120 ft
Area = 29Acres, 40 Acres
Two Year Pressure ProfileLate Time SLC
550 5000
Pressure, Psia
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Sims Gas Unit No. 1
0
250
500
750
1000
8/1/2004 8/1/2005 8/1/2006
GasRate&TubingPressure,(msc
f/D,psi)
0
250
500
WaterRate,bbl/D
MCFD
FTP
BWPDInstalled
Pumping Unit
East Texas Well
East Texas Field Example
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University7-6S No.2
0
250
500
750
1000
1250
1500
4/20/2004
5/20/2004
6/19/2004
7/19/2004
8/18/2004
9/17/2004
10/17/2004
11/16/2004
12/16/2004
1/15/2005
2/14/2005
3/16/2005
4/15/2005
MCFD
0
25
50
75
100
125
150
BOPD/BWPD
MCFD
BWPD
West Texas Well
West Texas Field Example
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Observations
Complex flow conditions can cause PA to incorrectly predict
flow geometry and drainage area.
Actual reservoir properties can be reproduced through PA
when the reservoir and the fracture are producing at a
pseudo steady state conditions. When these conditions are
not achieved, PA can not be expected to provide unique
solutions.
The cases presented highlight the need to incorporate all
available data into the analysis of the wells performance
and recognize the limitations of the technique being used to
analyze well performance.