ABSTRACT: Factors Controlling Simpson Group Production in Central Oklahoma
The distribution of oil production from within the Simpson Group has been considered enigmatic because all of the sandstone members are present throughout the study area, but some fields produce from all of the sandstone members and others produce from only one horizon. The Simpson shales are not capable of generating hydrocarbons and the oil produced from the Simpson Group probably originated from the Devonian/Mississippian Woodford Shale. The McClain County fault juxtaposed the Woodford Shale with the Simpson Group, which enabled lateral oil migration from the Woodford into the Simpson Group sandstones. Also, tortuous migration pathways allowed Woodford oil to ultimately accumulate in Simpson reservoirs, which involve downthrown younger rocks adjacent to upthrown older rocks.
Slight structural movements occurred contemporaneously with the deposition of the Simpson Group, creating semiparallel northeast-southwest-oriented thick and thin trends. Local structural movements were active during part or all of Simpson deposition. This created stratigraphic variations in the individual Simpson Group formations, which cause the apex of a field to migrate (or even vanish) with depth. Consequently, lower Simpson structures may not be reflected by upper Simpson structures, and conversely, upper Simpson structures may not continue with depth. Variations in Viola deposition enhanced the vertical discontinuity of structures within the study area so that mapped Viola structures may not reflect underlying Simpson structures. Furthermore, a dramatic change in the orientatio of the structural grain began to appear in the late Ordovician (Viola). Subsequent movements enhanced this later structural orientation, producing two acute structural trends that control the entrapment of oil. This study demonstrates that the dual structural imprint is probably the single most important factor in controlling the distribution and accumulation of hydrocarbons within the study area.
AAPG Search and Discovery Article #90991©1993 AAPG Mid-Continent Section Meeting, Amarillo, Texas, October 10-12, 1993.