Characterization of Tensleep Sandstone Reservoirs

Peigui Yin, Institute for Energy research, Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, phone: 307-766-2791, fax: (307) 766-2737, [email protected]

Three important components must be considered in the characterization of the Tensleep Sandstone reservoirs: (1) depositional boundaries, (2) petrophysical facies, and (3) permeability directionality. Depositional boundaries, resulting from grain size variation and diagenetic modification, potentially act as flow barriers and buffers in reservoir simulation. Regularly-oriented, high-ordered, depositional boundaries can also cause permeability directionality. Petrophysical facies are characterized by depositional texture, diagenetic fingerprints, porosity, and permeability. Six petrophysical facies are suggested in the Tensleep reservoir sandstones, including (1) uncemented, dolomite-sand-free, dune sandstone facies, (2) cemented, dolomite-sand-free, dune sandstone facies, (3) cemented, dolomite-sand-rich, dune sandstone facies, (4) uncemented, dolomite-sand-rich, interdune sandstone facies, (5) cemented, dolomite-sand-rich, interdune sandstone facies, and (6) cemented, dolomite-sand-rich sand sheet facies. Permeability directionality is very clear on the core-plug scale. In checked Tensleep sandstone cores, the maximum permeabilities range from 1.2 to 2.2 times the 90-degree permeabilities, and from 2.2 to 14.2 times the vertical permeabilities; and the 90-degree permeabilities range from 2.3 to 10.6 times the vertical permeabilities. Precise characterization of the depositional boundaries, petrophysical facies, and permeability directionality is critical for the geological modeling of Tensleep sandstone reservoirs.