Stratigraphic and geochemical investigation of kukersites (petroleum source beds) within the Ordovician Red River Formation, Williston Basin

Abstract

The Upper Ordovician Red River Formation has been a prolific producer of oil and gas in the Williston Basin, where it has cumulatively produced more than 750 million bbl of oil equivalent over the past half century. Previous studies have recognized petroleum source beds, referred to as kukersites, in the Red River Formation but have not determined their complete extent or hydrocarbon generation significance. Examination and analysis of 28 cores and greater than 300 wireline logs have revealed 10 distinct kukersites in the Red River D zone that can be correlated individually for tens to hundreds of miles (tens to hundreds of kilometers) across the western quarter of North Dakota. Although each Red River kukersite is typically thin (1–2 ft [0.3–0.7 m] thick), they combine to reach net thicknesses of greater than 12 ft (3.7 m) with average present day total organic carbon (TOC) values of typically 3–6 wt. %. Hydrogen index (HI) values from kukersite samples range from primarily greater than 800 mg hydrocarbons (HC)/g TOC within the northern flank of the basin to systematically decreasing to less than 100 mg HC/g TOC within the basin center. This systematic decrease in HI is interpreted to be a function of increased thermal maturity, where hydrocarbon generation has depleted kukersite organic richness. Preliminary calculations of hydrocarbon volumes generated from Red River kukersites, based on a previously developed method that calculates the volumetric decrease in original to present-day kerogen content, total approximately 66 billion bbl (1.05 × 1010 m3) of oil equivalent. This approximate generation total is more than enough to account for cumulative Red River production and supports the idea that the Red River is a self-sourced petroleum system with potentially significant remaining exploration potential.