The Pennsylvanian Desmoinesian Mudstone and Carbonates Reservoirs in Southern Denver Basin

Steven Tedesco

The southern part of the Denver Basin is undergoing resurgence in exploration for Atoka, Cherokee and Marmaton carbonate reservoirs with the reactivation of the Bolero field and the discovery of the Great Plains and Jolly fields in 2008. The traps are both stratigraphic and structural. The Atoka, Cherokee and Marmaton formations of Middle Pennsylvanian age in the Denver Basin contain numerous thin carbonaceous mudstones (one to eight feet thick) that are generating and expelling hydrocarbons. In some cases these mudstones are adjacent to thin highly porous, fractured carbonate reservoirs that cover large areas. The Atoka mudstones average 10% TOC which yield a high pour point 33 to 38 API gravity crude with associated 1,400 to 2,200 BTU gas. The organic matter within the Atokan mudstones is lacustrine in origin. The Cherokee and Marmaton mudstones average 11% TOC that yields a low pour point 35 to 41 API gravity crude with associated 1,450 to 2,100 BTU gas. The organic matter within the Cherokee and Marmaton mudstones is of marine in origin. The thin limestone and dolomites in the Cherokee known as 'A' and 'C' and the 'B' zone within the Marmaton have become the primary targets. This presentation will discuss some of the unique features and reservoir characteristics of the producing Pennsylvanian rocks in the Southern Denver Basin.

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