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Geology of Petroleum in Wind River Basin, Central Wyoming

William R. Keefer

The Wind River basin contains more than 60 oil and gas fields, located chiefly on structural traps that developed during Laramide deformation in latest Cretaceous and early Tertiary times. Seventeen different sedimentary formations are petroleum bearing. Principal reservoirs are the Pennsylvanian Tensleep Sandstone, Permian Park City Formation, and Cretaceous Cloverly, Thermopolis (Muddy Sandstone Member), and Frontier Formations.

Until latest Cretaceous time, central Wyoming was part of the foreland that sloped gently westward toward the Cordilleran geosyncline. Because (1) the regional dip of strata was westward, and (2) the overburden pressures always were greater toward the west, fluids tended to migrate as far eastward in the present basin area during the pre-Laramide period as structural and individual reservoir conditions permitted. Regional stratigraphic and structural relations suggest that some primary accumulation of hydrocarbons took place at or near presently known oil and gas fields before Laramide folding began.

Pronounced subsidence of the central basin area during the Laramide orogeny induced a secondary migration of fluids updip toward structural traps that developed contemporaneously along the basin margins. However, facies changes, unconformities, and porosity and permeability barriers within many of the pre-latest Cretaceous reservoirs tended to inhibit wholesale flushing of oil and gas formerly trapped in the central basin area. Therefore, unexplored stratigraphic traps possibly exist downdip from the present margins of the basin, especially where related to basinward-plunging anticlinal structures.

Exploratory drilling has not tested the Frontier and older Mesozoic rocks in about 3,500 sq mi of the central, structurally deepest part of the Wind River basin; Paleozoic rocks are untested in an area of 4,500 sq mi. The common reservoirs lie less than 15,000 ft below the present ground surface in approximately 2,000 sq mi of the untested areas.

 

AAPG Search and Discovery Article #91051©2012 AAPG Rocky Mountain Section Meeting, Albuquerque, New Mexico, 23-26 February 1969