Tensleep Formation

The Tensleep formation is a northwest/southeast-trending anticlinal structure on the east flank of the Big Horn basin. The reservoir is composed of five sandstone layers, approximately 200 ft [61 m] thick, divided by shale and shaley dolomitic stringers. Formation temperature averages 90°F [32°C]. 

Oil that has been discovered and produced from the Pennsylvanian Tensleep Sandstone (fig 11), the probable Lower Permian part of the Weber Sandstone in northwestern Colorado, and the middle Permian Park City Formation in central Wyoming probably has been derived from the Phosphoria Formation. Oil in the Lower Permian upper member of the Minnelusa Formation in northeastern Wyoming may have migrated into these reservoirs from the Phosphoria source beds, but carbonaceous beds in the middle member of the Minnelusa are a more likely source Cheney and Sheldon (33) speculated that petroleum originated in the organic-carbon-rich shale beds of the Phosphoria Formation and that the oil... 

Figure 11. Relation of oil reservoirs (solid patterns) in Pennsylvanian Tensleep Sandstone to carbonaceous shale beds of the Permian Phosphoria Formation and to inferred maximum depth of burial (thickness of Mesozoic rocks, in kilometers) shown by solid lines and supplementary 2.5- and 3,5-km thickness shown by dashed line.

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