130411 Slides.final [Compatibility Mode]

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4/10/201

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1

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

3

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?

5

Conditions

Reservoir geometriesStress dependent permeability

Radial composite

Two-layer system

Completion parametersHydraulic fracture clean-up and damage

Liquid loading

6

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

8

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

9

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

11

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

12

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

14

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

15

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

17

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

18

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

20

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

21

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

24

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

26

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

27

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

29

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?

30

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

32

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

33

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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34

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

35

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.

Documents

130411 Slides.final [Compatibility Mode]