Bakken and Madison Potential of the Powder River Basin
Geologic mapping shows that a western fairway of Early Mississippian/Late Devonian shale basins extends from Northern Canada south to East-Central Nevada. This western fairway is part of the ring of Early Mississippian/Late Devonian shale basins that surround the granitic core of the North American Continent. The Powder River Basin appears to be part of that trend. Excluding CBM wells, there are approximately 45,000 oil and gas wells in the Wyoming/Montana portion of the Powder River Basin. A structure contour map drawn on the base of the Darby Formation shows that only a handful of these wells go below the prolific Tensleep/Minnelusa Sandstone. These few wells are confined to the eastern shallow portion of the Powder River Basin. Available gamma ray curves of these few wells generally indicate the presence of a radioactive shale at the base of the Madison Limestone equivalent to the prolific Bakken Shale presently being exploited in the Williston Basin. The thermal maturity and source rock potential of these shales at present are unknown. Whether or not these shales are over-pressured or not is also unknown. Given the prolific oil production from the Bakken in the Williston Basin, these shales make attractive exploration targets. Furthermore, conodont dating of outcrop samples of Early Mississippian/Late Devonian age rocks strongly indicates that the remaining foreland basins in Wyoming as well as the western over-thrust belt have good exploration potential for Bakken Shale equivalent oil production. With the existing infrastructure of horizontal wells exploiting the Niobrara Shale in the Powder River Basin development, costs for horizontal wells in the Bakken equivalent should be at a minimum.
Likewise, the exploration potential of the Madison Limestone in the Powder River Basin has not been tested. In particular, the author has not been able to find any Madison Limestone tests in the deeper, western portion of the Powder River Basin located in Wyoming. However, a relatively small number of wells produce high water-cut oil from the Madison Limestone in Sage Creek Field. Sage Creek Field is located on the Crow Indian Reservation immediately east of the Big Horn Mountains. To date this is the only Madison Limestone oil production that the author has found in the Powder River Basin. Sage Creek Field is a relatively short distance from outcrops of the Madison Limestone to the west in the Big Horn Mountains. Paleokarst features are common in the Madison Limestone in outcrop along the east flank of the Bighorn Mountains. The high water-cut nature of the oil production and paleokarst suggest that the production is from hydrodynamically trapped oil. Sage Creek Field shows that the Madison Limestone, like the Bakken equivalent, has good exploration potential in the Powder River Basin. Whether development would be by conventional vertical wells or by horizontal wells is unknown at this time.
AAPG Datapages/Search and Discovery Article #90374 © 2020 AAPG Rocky Mountain Section Meeting, 2020 Vision: Turn Hindsight to Foresight, Grand Junction, Colorado, September 13-15, 2020 (CANCELLED)