Development of Structure and Porosity at Medicine Lake Field in Northeast Montana Williston Basin: ABSTRACT
Medicine Lake field produces oil from the Mississippian Charles, Devonian Winnipegosis, Silurian Interlake, and Ordovician Stony Mountain and Red River Formations. Drill-stem tests also show a potential for production from the Devonian Birdbear and Duperow Formations. Noncommercial quantities of oil were recovered from the Mississippian Mission Canyon Limestone and Ordovician Winnipeg Formation. Different combinations of bioclastic bank development, dolomitization, solution, and fracturing have contributed to the porosity of each of the producing formations. Porosity development in the Winnipegosis and Red River Formations may have been influenced by the Medicine Lake paleostructure. The Medicine Lake structure is slightly 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 Devonian time. On another structure at nearby Outlook field, structural movement can be shown to have continued into the Cenozoic. The configuration of Cambrian and Precambrian rocks at Medicine Lake suggests that the structure there formed by the 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 differentially eroded Precambrian land surface. End_of_Article - Last_Page 851------------