Geologic characterization and petroleum potential of the upper Cretaceous (Turonian) Wall Creek member and basement-involved hinterland vergent backthrusting, Salt Creek field, WY, U.S.A.

Abstract

The Upper Cretaceous (Turonian) Wall Creek Member of the Frontier Formation represents the distal reaches of a progradational clastic wedge that formed in response to the Sevier orogeny. Following uplift along the Sevier highlands, sediments were eroded and subsequently transported east and deposited into the Western Interior Basin (WIB). These deposits have been exploited for oil and gas since the late 19th century and still represent a prominent target for horizontal exploration in the Rocky Mountain region. At Salt Creek Field, oil and gas has been produced from the sandstones of the Frontier Formation for over 100 years from a large, asymmetrical, anticlinal trap. This study integrates core, wireline log, and 3D seismic data at Salt Creek Field to characterize the Turonian Wall Creek Member with respect to basin and field scale depositional processes, structure, and reservoir quality. Furthermore, re-interpretation of the deeper structure shows greater complexity than previously understood. Integration of publically available and unpublished core, wireline log, and 3D seismic data lead to new interpretations at Salt Creek Field that carry significant implications for exploration within the intermountain basins of Wyoming and throughout the Rocky Mountain region: 1) the asymmetrical anticline at Salt Creek Field formed as a fault-propagation fold induced by the occurrence of multiple (five) hinterland-verging back thrusts. The multiple backthrusts occurred in response to the eastward verging thrust that bounds the western margin of the PRB, a Laramide feature. 2) A linear, bar-like sandbody of coarse-grained, transgressive reworked deposits are observed at Salt Creek Field and lie between the delta front sandstones of the Upper Wall Creek Member and the overlying marine Cody Shale. These sandstones form a structurally enhanced stratigraphic trap and contain above average oil saturation. A similar, reworked transgressive sandstone is observed at Spearhead Field in the PRB. These sandstones represent an active target for oil and gas exploration. 3) A geometrically confined medium-grained sandstone with an erosive base is located at the base of the Wall Creek Member along a relatively thick southwest-northeast trending depositional fairway at Salt Creek Field. The fairway of deposition suggests lowstand incision and/or the presence of syndepositional paleostructural trends associated with basement lineaments that resulted in accommodation remnants. Similar sandbodies of the Muddy Sandstone provide excellent reservoirs and are actively explored for in the PRB.