Print this pageAbstract: Petroleum Potential and Stratigraphy of Simpson Equivalents in Arkansas and Adjacent Areas
The Simpson Group (Middle Ordovician) in Oklahoma is well known because of its petroleum potential; however, little is known about its equivalents in Arkansas and Missouri. Uncertainties with correlation, lack of published studies, and formational names that change at state lines hinder an understanding of these strata.
To alleviate this gap, an intensive effort was initiated in 1968 to describe and correlate the Everton-St. Peter from exposures in the Arkansas Ozarks and to study equivalent units, as well as the Joachim and Plattin, in the subsurface of petroleum-producing regions in the Arkoma basin of Arkansas and Oklahoma and the Black Warrior aulacogen in northeastern Arkansas.
The subsurface project involved the study of more than 60 wells in Arkansas, Missouri, and Oklahoma that spanned the Simpson succession. Seven regional stratigraphic cross sections trending east-west and north-south were constructed to show complex facies relations of potential sandstone and carbonate reservoirs. Major cycles of transgressions and regressions were defined and compared with those of the type Simpson in Oklahoma. Eustatic sea-level fluctuations over a stable craton and geosyncline margin provide a means by which these cycles may be recognized on a regional basis.
Despite facies complexity, lithostratigraphic units were traced satisfactorily throughout most of the subsurface. Exceptions, however, were the thick Arbuckle-Simpson carbonate successions in the Black Warrior aulacogen of northeastern Arkansas where cratonic unconformities and lithologic contrasts are absent. Insoluble residue analyses provide a means for differentiation. Here, too, the Smithville Formation "fills" the unconformable gap between the Arbuckle (Powell) and Simpson (Everton, St. Peter, Plattin).
Regional stratigraphic synthesis of the Simpson in Arkansas and surrounding regions is derived from isopach maps, percentage maps, and reconstructed cross sections. Geologic histories and paleogeography are also explained. The data suggest that the carbonate materials and lobate to sheet sands accumulated in a barrier island-shelf sea. The sands were partially reworked and modified by marine processes in transgressing seas. Secondary dolomitization of limestone was effective in producing intercrystalline porosity in selected areas of the Black Warrior basin.
Trends of favorable reservoir facies in the Everton and St. Peter are established in regions where production is from shallower and younger strata. Deeper targets in the Simpson therefore are suggested.
AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma