Abstract

The McPherson Anticline trends north-northeast-south-southwest and traverses the arch between the Salina and Sedgwick Basins in Kansas. This anticline extends 50 miles (80 km) and contains nine multipay oil and gas fields that produce from Paleozoic reservoirs. Subtle structural movement occurred throughout Paleozoic time, but the anticline is primarily a Late Mississippian–Early Pennsylvanian feature. It has a steeply dipping down-to-the-west fault on its western flank that has up to 400 feet (120 m) of throw. Culminations (and greater vertical offsets along the flanking fault) generally are adjacent to north-south-trending fault segments. Lesser vertical offsets along the flanking fault and structural sags are associated with north-northeast-south-southwest-trending fault segments. Reverse faulting is indicated by repeated stratigraphic sections encountered in wells, thus an overall right-lateral north-northeast-south-southwest wrench-fault regime can account for the distribution of structural traps.

The cross-fault juxtaposition of the Devonian-Mississippian Chattanooga Shale against a given pay zone may affect the chemical characteristics of the produced oils. Oils produced from Mississippian strata, relatively high in the section, have chemistries that suggest a mature Chattanooga Shale source rock and south-to-north migration up the crest of the anticline. Similarly, oils produced from pay zones in Ordovician rocks, where the Chattanooga Shale across the fault is shallower than the pay zone, are typical "Ordovician" oils of low relative maturity. If, however, because of faulting, an Ordovician pay zone is located above or directly against the Chattanooga Shale, then oils produced from the Ordovician pay zone may have compositions indicating mixing of Chattanooga Shale oils with "Ordovician" oils.