Potential for Minnelusa-Type Truncation Traps in Tensleep Formation, Bighorn Basin, Wyoming: ABSTRACT

Abstract

The Pennsylvanian Tensleep Formation in the Bighorn basin has potential for Minnelusa-type truncation traps. A dendritic drainage pattern on the upper Tensleep surface formed as a result of two regional unconformities. Subtle movements along basement faults locally controlled the orientation of drainages and valleys cut as these drainages were subsequently filled with Permian Goose Egg and Park City lithofacies. These later impermeable deposits may have acted as lateral barriers to petroleum migration within the Tensleep Formation. Reservoir potential of the Tensleep Formation depends upon both the environment of deposition and the degree of post-Tensleep erosion. The Tensleep consists of a dominantly marine lower member and a dominantly eolian upper member. This overall regressive sequence is punctuated by many transgressive surfaces. As a result, porous and permeable eolian sandstones are intercalated with marine carbonates and sandstones. These marine carbonates may act as permeability barriers, dividing the Tensleep into a series of discrete reservoirs as well. Depending upon the depth of incisement of the valleys and the amount of regional truncation, multiple reservoir systems are possible. Minnelusa-type truncation traps may exist in the Tensleep Formation where paleovalleys are oriented normal to regional dip. The best lateral seals would be provided by concave-downdipmore » curves in valley trends or by intersections of primary and secondary drainages.« less