Medicine Lake field produces oil from the Mississippian Charles, Devonian Winnipegosis, Silurian Interlake, and Ordovician Gunton and Red River formations, and drill-stem tests show a potential for production from the Devonian Nisku and Deperow Formations. Porosity in the field is the result of bioclastic bank development, dolomitization, solution, and fracturing. Porosity development in the Winnipegosis and Red River Formations may have been influenced by the Medicine Lake paleo-structure. The source of the oil in each of the producing formations is probably within that formation itself.

Figure

The Medicine Lake structure is roughly elliptical, 1 mi (1.6 km) in diameter, and has 125 ft (38 m) of structural closure at the top of the Red River Formation. Growth of the structure was essentially complete by the end of the Devonian. However, a similar structure at nearby Outlook field can be mapped from Paleocene outcrops, which shows that structural movement there continued into the Cenozoic.

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The configuration of Cambrian and Precambrian rocks at Medicine Lake shows that the structure there formed by compaction of Cambrian sediments deposited around a hill on the Precambrian land surface. Regional-scale southeast-plunging anticlines in the eastern Montana Williston basin may also have formed by compaction of Cambrian sediments on a differential eroded Precambrian land surface.

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