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History of the Cedar Creek Anticline, Southeast Montana

John Davis
Denbury Resources Inc.

Oil was discovered on the Cedar Creek Anticline in the Gas City Oil Field in 1951. Thirteen fields on the anticline have produced over a half billion barrels of oil from about 2700 wells. The Cedar Creek Anticline is a collection of structural traps, inter-connected by various faulting styles, including some subsets of fracture pattern overprinting. Located in southeast Montana, the anticline stretches 115 miles southeast from Glendive, Montana to Buffalo, South Dakota. The primary producing carbonate reservoirs include the Ordovician Red River, the Silurian Stoney Mountain and Interlake Formations, and Mississippian Mission Canyon Formation. The primary source rocks are the organic shales in the Cambrian Winnepeg Formation, Ordovican Lower Red River Formation, and lower Lodgepole Formation. All of the producing reservoirs, except the Mission Canyon, are intercrystalline and interpartical dolomites, and were deposited in supratidal, intertidal, and subtidal environments. The Mission Canyon reservoirs are mostly limestone. Shell Oil was the major explorer and developer of these fields from 1950 to 1998, and commenced water flooding and infill drilling from 1959 to 1984. Shell sold their intersts to Encore in 1999, whose focus was infill drilling for new oil. Denbury Resources Inc. bought Encore's interest in 2010, and current activities are centered on optimizing water flood patterns in prepation to commence CO2 floods in 2016. CO2 will be suppied via the 406 mile Denbury pipeline, under construction, starting from CO2 fields at Riley Ridge, and Lost Cabin Creek fields in Wyoming, and ending at Gas City, Montana.

AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013

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