The Gothic Shale of the Pennsylvanian Paradox Formation, Greater Aneth Field (Aneth Unit), Southeastern Utah: Seal for Hydrocarbons and Carbon Dioxide
By: Jason E. Heath, Thomas A. Dewers, Thomas C. Chidsey, Jr., Stephanie M. Carney, and S. Robert Bereskin
Greater Aneth oil field, Utah’s largest oil producer, has produced over 483 million barrels of oil. Located in the Paradox Basin of southeastern Utah, Greater Aneth is a stratigraphic trap producing from the Pennsylvanian Paradox Formation. Because Greater Aneth is a mature, major oil field in the western U.S., and has a large carbonate reservoir, it was selected to demonstrate combined enhanced oil recovery and carbon dioxide (CO2) storage. The Gothic shale seals the underlying Desert Creek oil reservoir, both in the Paradox Formation. Within the Aneth Unit in the northwestern part of the field, the Gothic is remarkably uniform, consisting of 7 to 26 feet (2–8 m) of black to gray, laminated to thin-bedded, dolomitic marine shale.
This 31-page Miscellaneous Publication is a detailed evaluation of the Gothic seal in the Aneth Unit and its effectiveness at supporting large CO2 and hydrocarbon columns in the Desert Creek reservoir below. This study includes geochemical, petrological, petrophysical, and geomechanical analyses that determined (1) the geologic controls on sealing effeciency, (2) effects of pressure changes on the seal due to CO2 injection and storage, and (3) possible chemical interaction between CO2 and the seal at its contact with the reservoir through time.