Stratigraphic Analysis of a Recent Discovery in the Missippian Lodgepole Limestone of the Williston Basin, North Dakota

Paul W. Grover

In Canada the Lodgepole Limestone has been divided, in ascending order, into the Carrington, Scallion, Virden, Whitewater Lake and Flossie Lake subintervaals. Correlation of these subintervals into the U.S. portion of the Williston Basin reveals three upward-shallowing cycles that filled the basin with prograding clinoform shaped packages.

A recent (2/93) well completed by Conoco at Dickinson field in Stark County, North Dakota, flowed 1000 bbl/day from a mound shaped feature in the lower Lodgepole Limestone. The producing zone occurs where the clean limestone of the Upper Virden highstand system tract thickens before thinning again toward the basin center. A core of the producing interval shows a fossiliferous wackstone with a high percentage of void filling cements containing both vuggy and fracture porosity. The underling en Shale also has productive fracture porosity just west of the mound where the clean limestones of the highstand systems tract overlies thermally mature en Shale in an area called the en fairway. Horizontal boreholes in the en Shale along the fairway may be draining fractures that extend from the en into the clean limestones above the shale.

If so, by carefully mapping the clean highstand system tracts of the Lodgepole Limestone and the thermally mature en Shale, one can predict where other productive mound features may exist.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995