Generalized structure map of Woodford Shale in eastern

Oklahoma (prepared by R. Vance Hall).

Overview of Woodford Gas-Shale Play of Oklahoma, U.S.A.

Brian J. Cardott

Abstract The Woodford Shale (Late Devonian-Early

Mississippian), an important hydrocarbon source rock in

Oklahoma (south-central United States), is age-equivalent

to Late Devonian gas shales in the United States (e.g.,

New Albany, Antrim, Ohio). It exceeds the minimum non-

negotiable parameters necessary for an economic gas

shale: gas source rock and fracture-able. Abundant oil-

generative organic matter (e.g.., Type II kerogen; 2-14%

total organic carbon) in the Woodford Shale is the source

of thermogenic methane and a bitumen network,

beginning in the late oil window, that are sites for gas

storage and migration. Abundant natural fractures in

silica-rich (30-87% quartz) lithologies of the Woodford

Shale in southern Oklahoma exposures illustrate

lithologies that develop induced fractures, required to

produce gas from shales in the subsurface.

Since 2004, more than 200 Woodford Shale gas wells

have been completed in eastern and southern Oklahoma

by using advanced completion techniques (e.g., frac

technology, horizontal drilling). Most interest is where

the Woodford Shale is in the condensate or dry-gas

window (>1.15% vitrinite reflectance, VRo), greater than

50 ft thick, and at relatively shallow depth (<12,000 ft) in

the western part of the Arkoma Basin where initial

potential gas rates up to 11 million cubic ft per day have

been realized. Thermal maturity of the Woodford Shale in

the Arkoma Basin covers a range of issues from possibly

lower gas rates and oil handling in the oil window

(<1.15% VRo) to gas composition changes at high

thermal maturity (>3% VRo). An additional Woodford

Shale gas play in south-central Oklahoma is primarily in

the oil window at relatively shallow depth (<7,000 ft).

Isopach map of Woodford Shale (from Comer, 1992)

Vitrinite isoreflectance map of Woodford Shale in eastern

Oklahoma (contoured by R. Vance Hall from data by B.J.

Cardott)

MISSISSIPPIAN

& OLDER

OUTCROP

AREA

CHOCTAW FAULT

11

1

1

4

3

3

2

2

2

1

1

1.31

0.56

0.790.59

0.78

2.19

0.64

0.64

2

1.73

2.09

1.371.79

1.98

1.870.57

1.23

1.050.86

0.74

1

0.72

3.32

2.69

0.52

2.94

0.58

0.5

0.55

0.57

0.58

0.830.77

1.14

1.230.79

2.53

0.57

0.560.6

1.69

0.82

3.462.4

2.442.48

3.41 3.43.6

3.363.44

4.85

6.36

4.76

0.590.56

0.54

0.49

0.57

0.5

0.5

0.5

0.56

2.81 3.47

2.252.26

1.88

0.52

0.64

0.62

0.63

1.88

1.89

2.52

2.51

0.49

0.51

1.15

1.66

1.622.85

0.94

1.61

2.01

1.58

2.31

1.03

PETRA 8/10/2007 11:30:29 AM

Woodford Shale Mineralogy (a, O’Brien and Slatt, 1990;

b, Kirkland et al., 1992; c, Greiser, 2006; d, Branch,

2007; e, Abousleiman et al., 2008)

a b c d e

Quartz 63-68% 29-87% 30-60% 9-61% 27-53%

K-Feldspar 4% 0-2% 2-10% 2-42% 0-2%

Plagioclase 3% 1-4%

Calcite 10% 5-25% 0-7% 0-11%

Dolomite 6-9% 0-56% 0-5% 0-10% 0-6%

Pyrite 5-7% 0-1% 0-5% 2-30% 1-13%

Total Clays 12-14%

Illite 8-35% 2-5% 7-53% 13-40%

Illite/Smectite 2-20%

Kaolinite 1-7% 2-5% 0-2% 0-5%

Chlorinite 2-5% 0-40% 0-5%

Woodford Shale gas well completions by major operator on

isoreflectance map, 2004-2008 (321 wells)

Oklahoma gas shale well completions, 1939-2008

(471 wells; 70 Caney wells; 401 Woodford wells)

Woodford Shale gas well completions by year, 2004-2008

(overlay of 2007 & 2008 wells; 389 wells)

0

20

40

60

80

100

120

140

160

180

200

1930 1940 1950 1960 1970 1980 1990 2000 2010

Year

Nu

mb

er

of

We

lls

0

20

40

60

80

100

120

140

160

180

200

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

Year

Nu

mb

er

of

Wells

Discovery

Wells

Woodford Shale gas well completions, 1939-2008

(405 wells)

553 ft

(IP 122 Mcf)

15,310 ft

(IP 234 Mcf;

7BO 42° API;

GOR 33,429)

0

50

100

150

200

250

1930 1940 1950 1960 1970 1980 1990 2000 2010

Year

Nu

mb

er

of

Wells

Caney

Woodford

Oklahoma Gas Shale Completion History (1939-2007)

Woodford Gas Shale Completion History (1939-2007) Woodford Shale Gas Field Discovery History Woodford Shale Well-Type History

0

20

40

60

80

100

120

140

160

180

200

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

Year

Nu

mb

er

of

Wells

Horizontal

Vertical

10

100

1,000

10,000

100,000

1,000,000

10,000,000

Ja

n-0

4

Ap

r-0

4

Ju

l-0

4

Oc

t-0

4

Ja

n-0

5

Ap

r-0

5

Ju

l-0

5

Oc

t-0

5

Ja

n-0

6

Ap

r-0

6

Ju

l-0

6

Oc

t-0

6

Ja

n-0

7

Ap

r-0

7

Ju

l-0

7

Oc

t-0

7

Date

Av

era

ge M

on

thly

Pro

du

cti

on

(M

cf)

Gas

Oil

352 Woodford wells (depth & IP pairs): depth 570-15,310 ft;

IP 3-11,200 Mcfd.

253 Horizontal Woodford Wells (depth & IP pairs):

depth 1,349-12,486 ft TVD; IP 3-11,200 Mcfd.

Initial Potential Gas vs Depth

1

10

100

1,000

10,000

100,000

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

Depth (feet)

Init

ial P

ote

nti

al (M

cfd

)

Woodford

Woodford Horizontal

41 Woodford Shale Oil/Condensate Producing Wells (2004-2007)

Woodford Shale Production (2004-2007)

Cumulative production from Woodford-only wells:

63,752,439 Mcf gas, 66,538 BBLS oil/condensate from 279

wells (excluding 23 OWWO; data from IHS Energy)

Woodford Shale Wells with Initial Potential Gas Rates >1MMcfd (226 of 405 wells)

THERMAL MATURITY AND STRUCTURE

Vitrinite reflectance of Woodford Shale in southern Oklahoma on Woodford

Shale structure map (Woodford Shale structure map prepared by Carlyle

Hinshaw in 1999; vitrinite-reflectance data by Cardott, in preparation).

SOUTHERN OKLAHOMA

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

0.00 0.50 1.00 1.50 2.00 2.50 3.00

Vitrinite Reflectance (%Ro)

Dep

th (

feet)

Tasmanites green

fluorescence indicates

immature thermal maturity

0.49-0.52% Rm

Tasmanites

green

fluorescence

0.50% Rm

Tasmanites

green

fluorescence

0.50% Rm

Tasmanites

green

fluorescence

0.56% Rm

Tasmanites

green

fluorescence

“Loss of fluorescence of Tasmanites

alginites is reached at a stage

corresponding to 0.9-1.0% Rr

(vitrinite)” Taylor et al., 1998, p. 137

Portion of subsurface structure map of Marshall County, OK (modified from Huffman,

1987). Structure contours drawn on top of Viola Group (ft below mean sea level).

100

1,000

10,000

100,000

1,000,000

19

70

19

73

19

76

19

79

19

82

19

85

19

88

19

91

19

94

19

97

20

00

20

03

20

06

20

09

Date

Av

era

ge

An

nu

al

Pro

du

cti

on

(M

cf)

GAS PRODUCTION IN OIL WINDOW

Two examples of gas production from

naturally-fractured Woodford Shale in the

Madill and Aylesworth anticlines in the

Ardmore Basin demonstrate gas production

with little or no reported oil production at

relatively shallow depths (e.g., @4,000 ft)

where the Woodford Shale is in the oil

window (@0.6% Ro). Even though Type II

Kerogen is capable of generating about 75%

of source-rock thermogenic methane by

1.1% Ro (Lewan, 2002), these examples may

be special cases where thermogenic gas

migrated into the Woodford Shale from

deeper in the Ardmore Basin. Gas isotope

data from these wells are not available.

100

1,000

10,000

100,000

1,000,000

Ja

n-9

0

Ja

n-9

2

Ja

n-9

4

Ja

n-9

6

Ja

n-9

8

Ja

n-0

0

Ja

n-0

2

Ja

n-0

4

Ja

n-0

6

Ja

n-0

8

Ja

n-1

0

Date

Av

era

ge

Mo

nth

ly

Pro

du

cti

on

(M

cf)

MADILL FIELD

Cimarex Energy of Colorado 3 Griffin-Olmstead well

Marshall Co.; NW¼ NW¼ NE¼ 16-5S-5E

Originally completed as oil well in McLlish (6,536-

6,544 ft) in 1955, oil workover well in McLish and

Bromide (5,664-5,696 ft) in 1956, and gas workover

well in Woodford Shale (4,052-4,135 ft) in 1992.

IP 747 Mcfd; Cumulative Woodford Shale gas

production of 1,792,734 Mcf from March 1992 to

October 2007 (data from IHS Energy)

SE AYLESWORTH DISTRICT FIELD

Verdad Oil & Gas Corp. 1 Mary Haynie well

Bryan Co.; NW¼ SE¼ SW¼ SE¼ 22-6S-7E

Originally completed as gas well in Misener sand

(4,192-4,227 ft) in 1956 and plugged back to Woodford

Shale (3,710-4,054 ft) in 1974.

IP 962 Mcfd; Cumulative Woodford Shale gas

production of 2,330,605 Mcf from November 1974 to

August 2007. Produced 178 bbls oil in 1995 (data

from IHS Energy)

Principal subsurface structural features in Marshall

County (from Huffman and others, 1987)

Structure contour map of the top of the Viola

Group (Ordovician) in the Aylesworth and SE

Aylesworth District fields (from Huffman and

others, 1987)

Structure contour map of the top of the Viola

Group (Ordovician) in the North Madill field (from

Huffman and others, 1987)

Cross section C-C’ of the SE

Aylesworth District field (from

Huffman and others, 1987)

Cross section D-D’ of the North

Madill field (from Huffman and

others, 1987)

3 Griffin-Olmstead

1 Mary Haynie

3 Griffin-Olmstead well

1 Mary Haynie well