(1) University of Wyoming, Laramie, WY
Abstract: The Teapot Sandstone: a progradational strandplain
The Campanian Teapot Sandstone in the southern Powder River Basin subsurface (Wyoming) is an oil-producing reservoir composed of coarsening- and thickening-upward lower shoreface deposits that prograded eastwards at least 40 miles. It is sharply topped by offshore shales, and has a gradational base to marine shales, with a funnel-shaped well-log response. Previous regional studies gave 0.2-2° eastward dip angles for the shaley 'foresets'.
About 130 electric and GR well-logs and 14 cores from Mikes Draw and Well Draw oil fields were examined. The Teapot Sandstone is interpreted in the study area as a progradational strandplain, rather than a delta as in previous works, composed of basinward-dipping shingled units with upper thick sandstones, passing basinwards to alternating sandstones and shales. The architecture records a horizontal basinward shift in shoreline trajectory, resulting from an increased sediment supply (related to Laramide uplift), and the low gradient of the Upper Campanian Western Interior Seaway.
In cross sections, the applied dip-correlation angle of ca 0.5° changes the interpretation of the internal geometry and the inferred flow paths through the reservoir. Along strike, the elongation of any unit is conspicuous, with an expected good connectivity over long distances. In a dip direction, however, the flow path should follow the relatively steep clinoform geometry. The connectivity of successive sand ridges depends on the presence and lateral extent of finer-grained or heterolithic intervals and could account for some compartmentalization of the reservoir downdip. Isopach maps of the units characterize the reservoir for enhanced oil recovery with water injection.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana