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Stratigraphy, sedimentology and petrophysics of the Tensleep Sandstone at Teapot Dome and in outcrop

Qingsheng Zhang, Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80401, phone: 303-273-3842, [email protected], Dag Nummedal, Colorado Energy Research Institute, Colorado School of Mines, Golden, CO 80401, and Peigui Yin, Institute for Energy research, Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071.

Two outcrops at the Middle Fork of the Powder River and at Fremont Canyon are chosen as analogs for the Tensleep Sandstone at Teapot Dome. Outcrop data include measured sections, high quality photo-mosaics, gamma ray logs, thin sections, drill plugs and GPS. Subsurface data include cores, well logs, thin sections and porosity and permeability data.

The Tensleep Sandstone contains multiple sequence boundaries in response to frequent and high-amplitude sea level changes. Evidence for sequence boundaries include paleosols, conglomerates, carbonate breccia, root traces and karst, all developed on top of marine carbonates. Generally, from bottom to top, the Tensleep Sandstone changes from dominantly marine, with abundant crinoids and corals, thick tabular carbonate beds and thin sandstone layers, to dominantly continental, with thick eolian cross-bedded sandstones, scarce fossils, and thin and discontinuous carbonates. The basal onlap of the Tensleep Sandstone from north to south reflects the presence of the Pathfinder Uplift to the south during Tensleep deposition.

The Tensleep Sandstone at Teapot Dome and in the upper part of outcrops consists of eolian deposits, interbedded with sabkha and shallow marine dolomites. Dolomites, even with lots of vugs, fractures and stylolites, do not form permeable reservoir because of extremely low permeability, and dead oil exists in many vugs and fractures. Sandstones are reservoir rocks, and six sandstone petrophysical facies are described according to deposition and diagenesis. Porosity and permeability are controlled by the petrophysical facies, and reservoir compartments are separated by sequence boundaries and bounding surfaces internal to the eolian deposits.