Stratigraphic Trap Accumulation in Southwestern Kansas and Northwestern Oklahoma

Abstract An oil-and gas-bearing inlier of Morrowan sandstones presents a paradoxical situation in that water, oil, and gas are present in an inverted structural relation, some of the gas being structurally lower than oil and water. A map of the pre-Pennsylvanian topography reveals that a modified trellis drainage system was developed on subaerially exposed Mississippian strata. Southwest-ward-tilted resistant limestones of the Chesterian Series stood out as subparallel cuestas; intervening erosional valleys developed on interbedded nonresistant shales. Morrowan strata were deposited under conditions of cyclic marine southwest-to-northeast transgression, which was interrupted by several minor regressions. Sands were deposited during the regressive phases, and shales during transgressive phases. Small-scale structural noses and closures on the Inola limestone are largely the result of differential compaction of shales deposited over buried pre-Pennsylvanian topography. Detailed mapping affords a logical explanation for each producing well and all but a few dry holes in the Second Morrow sand of the Harper Ranch field of Clark County, Kansas. The anomalous distribution of some gas accumulation is explained by Gussow’s principle, modified to apply to a stratigraphic trap.