Report of Investigations--KGS


Heavy-oil and bitumen resources in western Kentucky are present in the Upper Mississippian Big Clifty and Hardinsburg Sandstones and Lower Pennsylvanian Kyrock and Bee Spring Sandstone Members of the Caseyville Formation in a belt extending from Logan County on the south to Breckinridge and Hardin Counties on the north.

Net oil-saturated intervals in the tar sands range from 2.5 to 4.7 m thick, largely in downthrown fault blocks in and bounding the Rough Creek Graben. Records from 1,500 wells, analysis of reservoir properties from 3,769 plugs from 135 coreholes, and bulk volume of hydrocarbon calculated in 139 surface samples were evaluated using original quantitative methods, reinterpretation of prior qualitative results, and industry-standard petroleum-engineering principles. Median porosity of the tar-sand reservoirs is 14.8 to 19.8 percent, and median oil saturation is 17.4 to 34 percent. Mobile versus immobile oil in the pore space was calculated for five wells cored in Edmonson County in which permeability and porosity were measured before and after extracting all hydrocarbons in 393 core plugs. Median movable oil saturation in these cores was 40.7 percent of the total oil saturation in the Big Clifty, 26.9 percent in the Hardinsburg, and 61.9 percent in the Caseyville. Unrisked contingent and prospective heavy-oil and bitumen resources in place in the tar sands are estimated to total 3,346 million barrels of oil: 2,247 million barrels in the Big Clifty, 357 million barrels in the Hardinsburg, and 742 million barrels in the Caseyville. There are no demonstrable reserves. Overall, these resources are about 10 percent greater than previous evaluations.

The western Kentucky tar sands developed from microbial degradation of light oil during migration into the reservoir rocks, leaving heavily biodegraded pore-lining bitumen and mobile heavy oil. Pore-lining bitumen causes the reservoirs to be oil-wet, reducing effective permeability and porosity in a reservoir and decreasing oil recovery in enhanced-oil-recovery projects.

Since the collapse of the rock-asphalt industry in 1957, there has been no commercial process developed to date, either for enhanced oil recovery or for bitumen extraction from mined rock asphalt, to produce oil from the western Kentucky tar sands. In 2014, a new project was initiated to recover bitumen from the Big Clifty in northern Logan County; however, results of this project are inconclusive.

Publication Date



Series XII

Report Number

Report of Investigations 36

Digital Object Identifier (DOI)

Related Content

This evaluation was completed using data and information (herein collectively referred to as the data) in the possession of the Kentucky Geological Survey, some of which may be nonpublic data. The public data are available from the Kentucky Geological Survey Oil and Gas Records Database ( OGSearch.asp).