ABSTRACT

Since 1913, Mervine Field (27N-3E) has produced oil from 11 Mississippian and Pennsylvanian zones, and gas from two Permian zones. The field exhibits an impressive asymmetric surface anticline, with the steeper flank dipping thirty degrees east, maximum. A nearly vertical, basement-involved fault develops immediately beneath the steep flank of the surface anticline. Three periods of left-lateral wrench faulting account for 93 percent of all structural growth: 24 percent in post-Mississippian-pre-Desmoinesian time, 21 percent in Virgilian time, and 48 percent in post-Wolfcampian time.

The Devonian Woodford Shale (and possibly the Desmoinesian Cherokee and Ordovician Simpson shales) locally generated oil in Mesozoic through early Cenozoic time, which should have been structurally trapped in the Ordovician Bromide Sandstone. This may have joined oil already trapped in the Bromide, which had migrated to the Mervine area during the early Pennsylvanian from a distant source. Intense post-Wolfcampian movement(s) fractured the competent pre-Pennsylvanian rocks, allowing Bromide brine and entrained oil to vertically migrate up the master fault, finally accumulating in younger reservoirs.

Pressure, temperatures, and salinity anomalies attest that vertical fluid migration continues at the present time at Mervine Field. Consequently, pressure, temperature, and salinity mapping should be considered as a valuable supplement to structural and lithologic mapping when prospecting for structural hydrocarbon accumulations in intracratonic provinces.