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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