Assessment of undiscovered natural gas resources of the Arkoma Basin province and geologically related areas

Introduction

The U.S. Geological Survey (USGS) in 2010 completed an assessment of the undiscovered, technically recoverable petroleum resources of the Arkoma Basin Province, which includes the Arkoma Basin and Ouachita Thrust Belt, and two adjacent areas. The principle focus of this assessment is the Arkoma Basin of central Arkansas and east-central Oklahoma and the Ouachita Thrust Belt of southeast Oklahoma, southcentral Arkansas, and west-central Mississippi (fig. 1). Other areas assessed include (1) the Post-Ouachita Successor Basin of northeast Texas, south Arkansas, and north and northwest Louisiana; and (2) part of the Reelfoot Rift in northeast Arkansas and southeast Missouri (fig. 1).

The USGS assessment is based on geologic elements of a total petroleum system (TPS) that include (1) source-rock distribution, thickness, organic richness, thermal maturation, and petroleum generation and migration; (2) reservoir-rock type (conventional or continuous), distribution, and quality; and (3) character of traps and time of trap formation relative to petroleum generation and migration. Consideration of these TPS elements within a context of the reconstructed geologic history of each area, combined with analysis of historical petroleum exploration and production data, was used to estimate undiscovered, technically recoverable petroleum resources. This approach resulted in the definition of 5 TPSs containing 13 assessment units (AU, fig. 1). Undiscovered petroleum resources were estimated quantitatively for 10 of the AUs; no quantitative assessment was conducted for 3 of the AUs (table 1).

Arkoma - Ouachita Paleozoic Composite TPS Arkoma Shelf AU Arkoma Deep Basin Conventional AU Ouachita Thrust Belt AU Post-Ouachita Successor Basin AU Total Conventional Resources

Resource Summary

The USGS estimated mean values of 38,021 billion cubic feet of gas (BCFG) and 159 million barrels of natural gas liquids (MMBNGL) for undiscovered continuous and conventional resources in the Arkoma Basin and Ouachita Thrust Belt (table 1). No oil was estimated to occur in accumulations of 0.5 million barrels (MMBO) or larger.

More than 26 trillion cubic feet of gas (TCFG), 70 percent of the total undiscovered gas, occurs in shale-gas AUs defined within two formations. The Devonian-Mississippian Woodford Shale, from which more than 700 BCFG has been produced, is estimated to contain 10.7 TCFG in Oklahoma and western Arkansas (fig. 2A). The laterally equivalent Chattanooga Shale, which has not been a focus of historical exploration activity, is estimated to contain 1.6 TCFG in Arkansas (fig. 2A). The younger, Mississippian Fayetteville Shale, from which more than 700 BCFG has been produced, is estimated to contain 13.2 TCFG in two AUs in Arkansas (fig. 2B). The laterally equivalent Caney Shale, which has been a minor focus of historical exploration activity, is estimated to contain 1.1 TCFG in Oklahoma (fig. 2B).

The deep basin that straddles the boundary between the Arkoma Basin and the Ouachita Thrust Belt (fig. 1) has been interpreted to hold a basin-centered, continuous gas accumulation with tight-sandstone reservoirs of Pennsylvanian age. This Arkoma-Ouachita Foredeep Continuous AU is estimated to contain 6.8 TCFG, 18 percent of the total undiscovered gas. The Arkoma Coalbed Gas AU is estimated to contain 3.5 TCFG, 9 percent of the total undiscovered gas, in coals of Pennsylvanian age.

Conventional gas resources were assessed in three AUs containing reservoirs that range from Cambrian to Pennsylvanian age. The Arkoma Shelf, Arkoma Deep Basin Conventional, and Ouachita Thrust Belt AUs are estimated to contain 45 BCFG, 252 BCFG, and 753 BCFG, respectively (table 1). The sum of 1 TCFG for these three AUs represents 3 percent of the total undiscovered gas.

Figure 2. Specific boundaries for Arkoma Shale Gas assessment units (AU). (A) Two AUs in the Woodford and Chattanooga Shales, defined based on maps of high gamma-ray response in wireline logs. (B) Four AUs in the Fayetteville and Caney Shales, defined based on maps of high gamma-ray response in wireline logs and of thermal maturity. Results for all these AUs are shown in table 1. Area of map shown by dashed, black rectangle in figure 1.

Natural gas liquids were assessed in two shale-gas and two conventional AUs (table 1) and their presence is limited to the westernmost parts of the Arkoma Basin and Ouachita Thrust Belt, areas characterized by low thermal maturity (<1 percent vitrinite reflectance).

Three additional assessment units were defined and analyzed but not assessed quantitatively. These include the (1) Fayetteville Shale Gas – Mississippi Embayment AU (fig. 2B), (2) Elvins Shale Gas AU (Cambrian shale in the Reelfoot Rift, fig. 1), and (3) Post-Ouachita Successor Basin AU (Pennsylvanian-Permian strata; fig. 1). Each of these areas has been tested by a small number of exploration wells, some of which have yielded shows of petroleum but none of which has sustained production. These exploration histories, together with a paucity of geologic data to constrain a detailed analysis, led to the conclusion that insufficient information exists to warrant a quantitative assessment (table 1).

Photograph above: Exposure of the Devonian-Mississippian Arkansas Novaculite near Atoka, Oklahoma. The formation consists of thin interbeds of chert (blocky, resistant beds) and black, organic shale (recessive beds) and at this exposure is folded and faulted. The Arkansas Novaculite is a potential source and reservoir for conventional gas accumulations in the Ouachita Thrust Belt. Hammer with 1 foot handle near center of photograph for scale. Photograph by David W. Houseknecht, U.S. Geological Survey

For Further Information

Supporting geologic reports on the Arkoma Basin assessment are in preparation. These reports will be available as completed at the USGS Web site at: http://energy.cr.usgs.gov/oilgas/noga

Arkoma Basin Province Assessment Team:

David W. Houseknecht (Task Leader; dhouse@ usgs.gov), James L. Coleman, Robert C. Milici, Christopher P. Garrity, William A. Rouse, Bryant R. Fulk, Stanley T. Paxton, Marvin M. Abbott, John C. Mars, Troy A. Cook, Christopher J. Schenk, Ronald R. Charpentier, Timothy R. Klett, Richard M. Pollastro, and Geoffrey S. Ellis.

Photograph above: Exposure near Marshall, Arkansas of interfingering contact between the dark gray Fayetteville Shale and the overlying, buff colored Pitkin Limestone, both of Mississippian age. Elsewhere in the Arkoma Basin, the Fayetteville Shale is both the source and reservoir for a large continuous gas accumulation and the Pitkin Limestone locally is a reservoir for conventional gas accumulations. White object at lower-left is 1 foot long. Photograph by Stanley T. Paxton, U.S. Geological Survey.

Photograph above: Exposure near Marshall, Arkansas of interfingering contact between the dark gray Fayetteville Shale and the overlying, buff colored Pitkin Limestone, both of Mississippian age. Elsewhere in the Arkoma Basin, the Fayetteville Shale is both the source and reservoir for a large continuous gas accumulation and the Pitkin Limestone locally is a reservoir for conventional gas accumulations. White object at lower-left is 1 foot long. Photograph by Stanley T. Paxton, U.S. Geological Survey.

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