ABSTRACT
The Simpson Group and its equivalents are shown to have reservoir potential in the Arkoma basin and Ouachita overthrust region of Oklahoma and Arkansas.
The Simpson in Oklahoma, the Everton/St. Peter in Arkansas, and the Crystal Mountain/Mazarn/Blakely of the Ouachitas were studied in outcrop, and from well cuttings and logs to derive an understanding of (1) their stratigraphic relationships, (2) the nature and distribution of “Simpson” reservoir sands, (3) depositional and source environments, and (4) geologic history.
It was determined that sandstones of the Calico Rock, Newton, and St. Peter of Arkansas are equivalent to the Oil Creek, McLish (Burgen), and Bromide sandstones of Oklahoma, respectively. Further, the Crystal Mountain, lower Blakely, and upper Blakely sandstones of the Ouachitas are stratigraphically equivalent to the Oil Creek (Calico Rock), McLish (Newton), and Bromide (St. Peter), respectively.
The Everton/St. Peter is a mixed sandstone-carbonate association throughout most of the Arkoma but changes facies to carbonates in the eastern Arkoma basin and Mississippi embayment and is dominantly sandstone and shale in the southern and southwestern portions of the Arkoma basin in Arkansas. Similarly, the Simpson is a mixed sandstone-carbonate association in the Arkoma basin of Oklahoma, but is dominantly shale in the southern and southwestern portions of Oklahoma.
Sandstones of the Simpson and Everton/St. Peter were derived from a source to the north and were deposited in shifting strandline and shelf environments. Crystal Mountain and Blakely sands also were derived probably from the north but were deposited in deeper water fanlike environments via chutes on the downthrown sides of growth faults at the Arkoma basin (shelf) geosyncline transition. Substantial amounts of clay, however, were derived from a source to the south.
Regional cross sections, sand distribution maps, and paleogeographic maps are used to illustrate these ideas and to point out areas favorable for oil and gas exploration.
