Source Rock Potential of Upper Devonian-Lower Mississippian Formations in Oklahoma and Western Arkansas

John B. Comer

In most parts of Oklahoma and Arkansas, Upper Devonian-Lower Mississippian formations are excellent petroleum source rocks with prolific hydrocarbon-generating capability. Exceptions occur in the core area of the Ouachita system where less organic-rich lithologies (chert, siltstone, light-colored shale) are commonly found, and in the deep northwestern part of the Anadarko basin where silty shale predominates.

Regional variations in organic richness reflect Late Devonian-Early Mississippian paleogeography, with the Ouachita core area representing a deep trough in which open ocean circulation prevailed. The Anadarko basin was more restricted, and terrestrial sediments were transported from northwestern source areas to the southeast along the basin axis.

In central and southern Oklahoma, Upper Devonian-Lower Mississippian strata are rich oil source beds (mean = 7% TOC) at an early stage of generation. The major accumulations of oil in this region have been documented as coming from the Woodford formation. Equivalent-age source rocks in the deep part of the Anadarko basin have matured to or beyond the gas generation stage and significant gas generation is still occurring within parts of the basin.

Around the Ozark uplift, age-equivalent rocks contain less organic matter (mean = 3.5% TOC) and more terrigenous clastic sediment than in central and southern Oklahoma. Both oil- and gas-generating types of kerogen are present and the organic matter has reached the early to main stages of oil generation.

Upper Devonian-Lower Mississippian source rocks in the Ouachita core area are metamorphosed and no longer have significant hydrocarbon-generating capability. Age-equivalent rocks in the frontal zone are rich oil source beds at an early stage of generation. Significant hydrocarbon accumulations are possible at depth within the frontal zone and from frontal zone rocks that have been overthrust by metamorphosed Ouachita core-area rocks, particularly in the northwestern part of the Ouachita province.

AAPG Search and Discovery Article #91039©1987 AAPG Mid-Continent Section Meeting, Tulsa, Oklahoma, September 27-29, 1987.