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The AAPG/Datapages Combined Publications Database

Williston Basin Symposium

Abstract

MTGS-AAPG

Seventh International Williston Basin Symposium, July 23, 1995 (SP12)

Pages 203 - 208

Tectonic Controls On the Lodgepole Play in Northern Stark County, North Dakota — Perspectives from Surface And Subsurface Studies

George W. Shurr, St. Cloud State University, St. Cloud, Minneapolis
Allan C. Ashworth, North Dakota State University, Fargo, North Dakota
Randolph B. Burke, North Dakota Geological Survey, Bismarck, North Dakota
Paul E. Diehl, North Dakota Geological Survey, Bismarck, North Dakota

ABSTRACT

Waulsortian-like mounds in the lower Lodgepole Formation (Mississippian) near Dickinson, North Dakota, have produced more than three-quarter million barrels of oil in less than two years. Mound formation occurred in a paloetectonic setting of a mosaic of lithosphere blocks. Post-depositional fracturing was controlled by subsequent block reactivation.

Northwest and northeast linear features visible on satellite images outline the mosaic of lithosphere blocks. Regional structures on a shallow marker in the Pierre Shale (Cretaceous) include a north­east-trending syncline. The productive, fractured mounds are located on a relay ramp connecting normal faults along block margins at the northwestern side of the regional syncline. Oblique-slip normal faults that correspond with block boundaries also occur in nearby outcrops of Tertiary rocks. Faulted strata are Paleocene to possibly Miocene in age, so faulting and fracturing may be post-Miocene.

The structural configuration of deeper Paleozoic formations changes; the regional northeast-trend­ing syncline that is present on the top of the Minnekahta Formation (Permian) is absent on the Tyler (Pennsylvanian) or deeper formations. Although the relay ramp is indiscernible on the top of the Tyler, the block with mounds does have structural expression. That block also has possible paleotec-tonic implication as shown on the map of lower Lodgepole thickness. Specifically, the block has elongated thin and thick areas along the southwest and northeast margins, respectively. Core observations indicate that vugs provide most of the reservoir porosity. Fractures that connect the vugs account for most of the permeability.

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