Optim ization of Infill Drilling in Naturally-FracturedOptim ization of Infill Drilling in Naturally-FracturedTight-Gas Reservoirs of the San Juan BasinTight-Gas Reservoirs of the San Juan Basin

Lawrence W. Teufel

Petroleum Engineering DepartmentNew Mexico Institute of Mining and Technology

Socorro, New Mexico

Project Team• Her-Yuan Chen – Well test and production analysis• Tom Engler – Reservoir characterization and simulation• Bruce Hart – Geophysical studies• Mike Kelly – Reservoir simulation• John Lorenz – Characterization of natural fractures

Acknowledgments• Project is supported by NETL with DOE/Industry Cooperative

Agreement DE-FC26-98FT4086

• Industry Partners- BP- Burlington Resources- Conoco-Philllips Petroleum- Williams Energy

• NM Tech - Industry Consortium on Naturally-Fractured andStress-Sensitive Reservoirs

Optimization of Infill Well Locations in Naturally-FracturedTight-Gas Reservoirs Requires a Multi-Disciplinary Approach

• Reservoir characterization to determine reservoir heterogeneity, net paythickness, and effective porosity from integrated log analyses.

• Characterization of natural fracture systems to determine orientation,distribution, and intensity from geological and geophysical studies; and assessinfluence of fractures on reservoir permeability and permeability anisotropyfrom numerical models.

• Analyses of well tests and production data to determine reservoir permeabilityand permeability anisotropy.

• Reservoir simulation studies to determine - distribution of net pay, effective porosity, and reservoir permeability - well drainage shape and area - distribution of reservoir pressure and potential well interference - optimal location and number of infill wells - forecast of increased gas recovery.

Generalized Stratigraphy of San Juan BasinGeneralized Stratigraphy of San Juan Basin

MES

OZO

ICC

ENO

ZOIC

ERA SYSTEM FORMATION THICKNESS PRODUCTION

Naturally-Fractured Tight-GasSandstone Reservoirs

Mesaverde Group

Porosity : 6 – 12%

Permeability : < 0.01 D (Matrix)

0.01– 60 D (Reservoir)

Pore Pressure : 0.23 psi/ft

Overburden Stress : 1.03 psi/ft

San Juan BasinSan Juan Basin

Vertical Partially-Filled Extension Fracture inVertical Partially-Filled Extension Fracture inMesaverde CoreMesaverde Core

N

Orientations of Natural Fractures inMesaverde Sandstone at Heron Lake, NM

Fracture Network in DakotaFracture Network in DakotaSandstone OutcropSandstone Outcrop

N

Fracture Network MapFracture Network Map

10 m

Reservoir Permeability is AnisotropicReservoir Permeability is Anisotropic

kmin = 0.03 mD

kmax = 3.34 mD

kMatrix = 0.01 mDN10 m

Com parison of W ell Drainage AreasCom parison of W ell Drainage Areas

ba

k

Isotropic Anisotropic

kminkmax

`

kminkmaxk

Optim al Location of Infill W ell is Optim al Location of Infill W ell is Dependent on Shape of Drainage AreaDependent on Shape of Drainage Area

`

kminkmax

Rotation of Offset W ells Elim inates DrainageRotation of Offset W ells Elim inates DrainageOverlap and Increases Drainage of ReservoirsOverlap and Increases Drainage of Reservoirs

with Anisotropic Perm eabilitywith Anisotropic Perm eability

Increase in Cum ulative Production for Offset W ellIncrease in Cum ulative Production for Offset W ellRotated 10° from M axim um Perm eabilityRotated 10° from M axim um Perm eability

DirectionDirectionC

umul

ativ

e Pr

oduc

tion

[BSC

F]

1960 1965 1970 1975 1980 1985 1990 1995 20000

0.2

0.4

0.6

0.8

1

1.2

1.41.6

1.8

MesaverdeFormation

Kmax / Kmin = 10

Gas Recovery Increases with Rotation OfGas Recovery Increases with Rotation OfW ell Alignm ent from Direction of M axim umW ell Alignm ent from Direction of M axim um

Perm eabilityPerm eabilityIn

crea

sed

Rec

over

y [%

]

45

40

35

30

25

20

15

10

50

0 10 20 30 40Well Alignment [deg]

Kmax / Kmin = 10

MesaverdeFormation

Natural Fractures and Drainage AreaNatural Fractures and Drainage Area

Production from tight-gas sandstone reservoirs of the Mesaverdeand Dakota formations in the San Juan Basin is highly dependenton natural fractures.

Fractures not only enhance the overall permeability of thesereservoirs, but also create significant permeability anisotropy.

Permeability anisotropy causes the drainage area around wells tobe elliptical.

Elongated drainage creates more production interference anddrainage overlap between adjacent wells and increase the potentialfor leaving large sections of the reservoir undrained.

Pilot Study Areas in San Juan BasinPilot Study Areas in San Juan Basin

Outcrops ofPictured Cliffs FM

CONM

Farmington

Cuba

Mesaverde& DakotaPlays

20 mi

N

27N5W28N7W

29N7W30N8W

31N6W31N12W32N11W 32N10W

`

N

Deviation from north

New infill well

Existing well

DrainageKmin

Kmax

W ell Drainage Area in Reservoir withW ell Drainage Area in Reservoir withAnisotropic Perm eabilityAnisotropic Perm eability

`

Form ation Pressure in Offset W ells IncreasesForm ation Pressure in Offset W ells Increaseswith Increasing Rotation from Direction ofwith Increasing Rotation from Direction of

M axim um Perm eabilityM axim um Perm eabilityD

evia

tion

from

N/S

[deg

]

350 400 450 500 550 600 650 700 750 8000

5

10

15

20

25

30

3540

45

SICP [psi]

`

Elliptical Drainage Area Is Aligned withElliptical Drainage Area Is Aligned withM axim um Perm eability DirectionM axim um Perm eability Direction

Kmin

Kmax

Existing wellDrainage

Model boundary

N

POW 1 mile

Infill Drilling W ill Increase Gas RecoveryInfill Drilling W ill Increase Gas Recovery

1990 2000 2010 2020 2030 2040 20500

10

203040

50

6070

8090

100

BC

F

Proposed 80acre spacing

Existing wells on160 acre spacing

12 34

BC

F

160 acrespacing

90807060

50

4030

2010

0

80 acrespacing

Current wells 1 well persection

2 wells persection

3 wells persection

4 wells persection

Infill Drilling W ill IncreaseInfill Drilling W ill IncreaseGas RecoveryGas Recovery

`

Elliptical Drainage of W ells Is AlignedElliptical Drainage of W ells Is AlignedW ith M axim um Perm eability DirectionW ith M axim um Perm eability Direction

Kmin

Kmax

Existing wellDrainage

Model boundary1 mile

N

`

Infill Drilling will Increase Gas RecoveryInfill Drilling will Increase Gas Recovery

Proposed 80acre spacing

Existing wells on160 acre spacing

4321

70

60

50

40

30

20

10

01980 1990 2000 2010 2020 2030 2040

BC

F

`

Infill Drilling W ill Increase Gas RecoveryInfill Drilling W ill Increase Gas Recovery

4 wells persection

New wellsOld wells

80 acrespacing

160 acrespacing

3 wells persection

2 wells persection

1 well persection

Current wells

70

60

50

40

30

20

10

0

BC

F

High Fracture Intensity

Low Fracture Intensity

High Fracture Intensity(With Isotropic Permeability)R

ecov

ery

per w

ell [

BC

F]

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.01

Number Infill Wells/Section2 3 4

Potential for Increased Recovery IsPotential for Increased Recovery IsGreater In Reservoirs with Low FractureGreater In Reservoirs with Low Fracture

IntensityIntensity

Existing Wells Infill Wells

93A

93R

47

47B

47A

64B64C

57C57A 64

64A57

57B

37

37B 37C

38A

38

37A

85B 85C

84AC85

85A 84

Section 2 Section 1

Section 11 Section 12

Well Locations for Pilot 29N7W

Cum

. Gas

Pro

duct

ion,

BC

F

80

70

60

50

40

30

20

10

0No Infill Wells Hypothetical

Wells On NS Direction

Actual Well Locations

80 Acre Infill Drilling

Cumulative Gas Production Forecast for Pilot 29N7W

Production Forecast of Infill Wells for Pilot 29N7W

Cum

. Gas

Pro

duct

ion,

MM

cf

3000

2500

2000

1500

1000

500

0

80 Acre Infill Drilling

57A 57B 64B 85C 47B 57C 93R 37B 64C 85B

3500

39%

69%

39%29%

12% 49%62%

7% 95%

67%

50%

Actual Well Location

Hypothetical Well on NS Direction

Infill Wells

`

Fracture Swarm s EnhanceFracture Swarm s EnhanceReservoir Perm eability AnisotropyReservoir Perm eability Anisotropy

Kmin

Kmax

Existing wellDrainage

1 mile

Kmin

Kmax

Fracture swarm

N

SUM M ARYSUM M ARY

Reservoir characterization and simulation studies are beingconducted on naturally-fractured tight-gas reservoirs in theSan Juan Basin to

(1) Define the elliptical drainage area and recoverable gas for existing wells,(2) Determine the optimal location and number of new infill wells to maximize economic recovery,(3) Forecast the increase in total cumulative gas production from infill drilling at different locations in the basin.

Optimal infill drilling of the Mesaverde formation in the San JuanBasin may increase recoverable gas by 7.8 TCF.