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Stratigraphic and Geochemical Investigation of Kukersites (Source Beds) Within the Ordovician Red River Formation, Williston Basin, North Dakota


The Ordovician Red River Formation has produced over 600 million barrels of oil equivalent from the Williston Basin, over half of which has come from North Dakota. Red River hydrocarbons were originally thought to be externally sourced by the underlying Icebox Formation. However, various studies have described and examined kukersites within the Red River Formation. Kukersites are organic-rich carbonate beds that contain G. Prisca alginate (Type I kerogen), formed in an offshore marine setting, and may be the source of Red River hydrocarbons. In core, kukersites are dark grey to black, fossil-bearing in part, faintly laminated to moderately bioturbated, average 1-10 wt. % TOC, and range from inches to several feet in thickness. On wireline logs, kukersites display elevated resistivity, sometimes elevated log porosity, and negligible gamma ray signatures. Nine Kukersites can be correlated across western North Dakota within the D interval/C burrowed member. These kukersites combine for 14-15 ft. net thickness with an average of 4-5 wt.% TOC within west-central North Dakota, 6-8 ft. net thickness along the Saskatchewan and South Dakota borders, and pinch-out to the east at 30-60 miles from the Montana border. Moving from areas of lower to higher thermal maturity, kukersite core samples transition from averaging reliable Tmax values of 449° up to 460° while hydrogen index values decrease from averaging over 500 mg HC/g TOC to less than 100; thus indicating significant hydrocarbon generation has occurred. Similarly, the API oil gravity and gas to oil ratios of hydrocarbons produced from discontinuous reservoirs proximal to the kukersites (D interval/C burrowed member) both increase along with the thermal maturity of the kukersite source beds. The thermal maturity of kukersites and proximally produced hydrocarbons increases towards the central, deeper portions of the basin. Red River thermal maturity also extends along an elongate north-south trend that parallels the Nesson, Little Knife, and Billing Nose anticlines which does not always follow depth. Utilizing net thickness, geochemical, and thermal maturity data, preliminary hydrocarbon generation calculations indicate Red River kukersites have generated over 20 billion barrels of oil equivalent within North Dakota. This preliminary generated hydrocarbon volume greatly exceeds cumulative Red River production and indicates the possibility of vast remaining hydrocarbon volumes.