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Play Start Page Play Summary Resources Kansas Info Region: Northern Midcontinent
System: Pennsylvanian


This Atokan Play information is from the U. S. Geological Survey 1995 National Assessment of United States Oil and Gas Resources (available on CD-ROM from the U.S.G.S. as Digital Data Series DDS-30, Release 2).

Atokan Sandstone Stratigraphic Gas Play

by Mitchell E. Henry and Timothy C. Hester

Much like Morrow Group strata, Atoka Group strata are oriented in a broad band that occupies most of the province, except that part along the northeastern and southwestern edges of the province where absent. Unlike the Morrow Group, Atokan strata include a significant number of hydrocarbon-producing limestone reservoirs. The limestone and sandstone reservoirs are separated geographically, with the limestone reservoirs more prevalent in the central and northwestern part of the province and the sandstone reservoirs more prevalent in the southeastern part. Therefore, the Atokan Sandstone Stratigraphic Gas Play includes all Atokan Group rocks southeast of a line that runs from about T. 13 N., R. 26 W. in Roger Mills County, Okla., to about T. 19 N., R. 14 W. in Dewey County, Okla., except that part included in the Deep Stratigraphic Gas Play. Depths range from about 7,000 ft in the northeast part of the play where the Atoka Group is truncated to 13,000 ft at the southern play boundary (the upper depth limit of the Deep Stratigraphic Gas Play).


Reservoir rocks in this play are all sandstones of the Early Pennsylvanian Atoka Group. Predominantly shale with locally developed sands (Bingham, 1993), the entire Atoka Group ranges in thickness from truncation along the northeastern and southern parts of the play to about 500 ft at the southern play boundary (adjacent to the Deep Stratigraphic Gas Play). Bingham (1993) reported average porosity values of about 8 percent for each of 2 Atokan reservoirs in the southern Anadarko Basin. Atoka Group reservoirs are, for the most part, stratigraphically imbedded in shales and are expected to be of fair quality where they exist.

Source rocks

The most likely hydrocarbon sources for this play are Atoka and Morrow Group shales, which are either interbedded with Atoka reservoirs or in the adjacent group of strata. Because Atoka Group rocks are thin and directly overlie the Morrow Group, they have a similar thermal history. That is, Atokan rocks throughout the play have reached or exceeded the level of thermal maturation required for the onset of oil generation (Ro > 0.6 percent). The area of major Atokan sandstone production, however, is much more restricted. Poor reservoir quality or perhaps an overall lack of reservoir rock are possible explanations for the limited distribution of production. All major accumulations in this play are gas, therefore, the source may be Morrowan shale, which has abundant type III organic matter (Burruss and Hatch, 1989). High thermal maturation levels near the boundary of the Deep Stratigraphic Gas Play may also have generated some gas from the type II kerogen, or generated but did not expel oil.

Timing and migration

Timing of trap formation and hydrocarbon generation is favorable for the charging of reservoirs in this play. Petroleum generation probably began between 300 and 250 Ma in this play (Schmoker, 1989). The limited distribution of production in this play requires only short distance migration of hydrocarbons.

Traps and exploration status

Trap types for this play include stratigraphic (Bingham, 1993) and combination. Seals are formed by Atokan and Desmoinesian shales. Major reservoirs range in depth from approximately 9,700 to 13,000 ft. Reported well penetrations for the entire Atoka Group number only about 8,400, as compared to about 26,000 for the entire Morrow Group. This number may be low because of the difficulty in determining the top of the Atoka Group in the subsurface. The actual number of well penetrations is probably similar to, or greater than, that of the Morrow Group (~26,000). Consequently, the Atoka Group is probably at least as well explored as the Morrow Group. Of the 8,400 well penetrations in the Atoka, about 542 are hydrocarbon producers. Six major accumulations are assigned to this play; all are gas. The largest accumulation is at Watonga-Chickasha Trend with an estimated ultimate recovery of 320 BCFG. All major future discoveries are also expected to be gas.

Resource potential

Because of the relatively high level of exploration and the general lack of major discoveries, the potential for future major discoveries in this play is considered limited. The very localized nature of sand development (Bingham, 1993) may be the most serious limitation for future discoveries in this play. Historical production and well completion data are the foundation for the assessment of this play.

Play Map

map showing fields in this play


Bingham, T.L., 1993, Atoka marine sandstone--Anadarko basin, Oklahoma, in Debout, D.G., White, W.A., Hentz, T.F., and Grasmick, M.K., Atlas of major Midcontinent gas reservoirs: p. 40.

Burruss, R.C., and Hatch, J.R., 1989, Geochemistry of oils and hydrocarbon source rocks, greater Anadarko basin--evidence for multiple sources of oils and long-distance oil migration, in Johnson, K.S., ed., Anadarko Basin Symposium, 1988: Oklahoma Geological Survey Circular 90, p. 53-64.

Schmoker, J.W., 1989, Thermal maturity of the Anadarko basin, in Johnson, K.S., ed., Anadarko Basin Symposium, 1988: Oklahoma Geological Survey Circular 90, p. 25-31.

Kansas Geological Survey, Digital Petroleum Atlas
Updated July 16, 1996
Comments to webadmin@kgs.ku.edu