Hydrocarbon Assessment in Two Midcontinent Provinces: Salina and Sedgwick Basins

S. E. Prensky

The 1995 U.S. Geological Survey National Assessment of undiscovered hydrocarbons employed a play approach. In the Sedgwick basin (south-central Kansas) and Salina basin (eastern half of Nebraska and the north-central part of Kansas) three hydrocarbon plays were defined: lower Paleozoic, Mississippian, and Pennsylvanian.

The lower Paleozoic play consists of combination traps in which locally sourced (Ordovician Simpson) oil and gas are trapped in sandstone or carbonate reservoirs that are situated on low-relief anticlinal closures and noses or trapped by the stratigraphic pinchout underlying either the pre-Pennsylvanian or the pre-Chattanooga unconformities. The Mississippian play consists of combination traps in which migrated (Devonian Woodford) oil and gas are trapped in (1) basal sandstone, (2) carbonate, and (c) chert on low-relief anticlinal structures; porosity is controlled, in part, by updip facies changes or by paleotopography and paleostructure. The Pennsylvanian play consists of combination traps in which locally sourced (Pennsylvanian) and migrated (Woodford?/Simpson?) oil and gas are tra ped in Pennsylvanian sandstone and carbonate reservoirs, primarily within the Missourian-age Lansing and Kansas City Groups, on anticlinal closures with stratigraphic controls; multiple pay zones are common.

Analysis of trends in different expressions of discovery rate versus exploration effort, based on the extensive 90-year exploration history, suggests that the potential for large (>1 MMBOE) undiscovered accumulations in this mature province is extremely low.

The Salina basin province is immediately north of the Sedgwick basin. Despite numerous oil shows in the Kansas part of the province and the fact that much of the Nebraska part is mostly untested, this basin is considered essentially non-productive. The lack of source rock and the thermal maturity in most of the basin suggest little to no potential for large accumulations (>1 MMBOE) of undiscovered hydrocarbons. The oil that has migrated into this basin is restricted to the southern rim of the basin (Saline and Dickinson Counties) and is evaluated within the plays defined for the Sedgwick basin.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995