U.S. Geological Survey research core of the Niobrara Member of the Mancos Shale, Delta, Colorado

Sarah Hawkins, Mark Kirschbaum, and Christopher Schenk

The main objective of the U.S. Geological Survey's (USGS) National Assessment of Oil and Gas Resources Project is to assess the technically recoverable undiscovered conventional and unconventional resources of the United States. A critical element for any assessment is the existence of source rocks capable of generating hydrocarbons. The Upper Cretaceous Mancos Shale is a thick widespread marine mudstone in the Rocky Mountain region for which there is limited data for a quantitative resource assessment. In 2011, the USGS obtained some 800 ft of continuous core of the latest Turonian through middle Santonian Niobrara Member of the Mancos Shale north of Delta, Colorado, where the formation is thermally immature. The core, AB-2-11, is critical for determining productive gas and oil zones within the Niobrara Member, and might serve as an analog for other areas once covered by the Western Interior Seaway. About 15 miles southeast of AB-2-11, the USGS previously (2005) cored thermally immature Cenomanian through Turonian strata in the Candy Lane #1; together they provide nearly 1,500 ft of core of the lowermost Mancos Shale. Initial geochemical results from Candy Lane #1 indicate that intervals within the lower Mancos Shale are of source rock quality, with total organic carbon (TOC) content as much as 4 wt % and hydrogen index values that range from 380 to 520 mg HC/g TOC. Further geochemical analyses of the AB-2-11 core will provide information critical to the assessment of unconventional resources in the Mancos Shale.

AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012