An Analysis of a Near-Surface Big Clifty (Jackson) Sandstone Reservoir in Logan County, Kentucky

Abstract

The Big Clifty (Jackson) Sandstone Member of the Golconda Formation is the most important of the Mississippian (Chesterian) heavy-oil reservoirs in the southeastern Illinois Basin. Heavy oil reservoirs, or asphalt rock deposits, have been studied extensively in south central and western Kentucky, and ~2 billion barrels of original oil in place (OOIP) is proposed to occur in the Big Clifty. Heterogeneities related to depositional facies changes are poorly understood in Kentucky, where the Big Clifty has been mostly described as a 60-120 feet thick sandstone unit. In some locations, in contrast, such as at the Stampede Mine in Logan County, the Big Clifty occurs as two distinct sandstone bodies with intercalated mud-rich units. Currently no predictable depositional model exists to explain abrupt facies changes observed during open pit mining conducted over the last couple of years.

This study integrates sedimentological, stratigraphic, and geophysical datasets to characterize the lithological changes occurring in Big Clifty reservoirs and may be used as a model down dip into the basin where conventional-oil Jackson reservoirs are targeted. Datasets used in this study include over 30 cores retrieved from across Stampede Mine's acreage, surface-mine exposures, Electrical Resistivity Tomography (ERT) surveys, and bitumen concentration values.

The Big Clifty Sandstone formed in a tidally influenced deltaic system occurring on a low-angle dipping ramp. Shallow marine ichnofacies occur in rhythmically bedded deposits. A brecciated mudstone and red-green shale occurs above the lower sandstone reservoir. This muddy facies represents an exposure surface that separates regressive and transgressive parasequences. Sedimentary features and bitumen concentration vary across the exposure surface making bitumen concentration trends difficult to ascertain without close subsurface control. The extent of channelized sandstone bodies and bitumen-rich units however can be generally documented.

AAPG Datapages/Search and Discovery Article #90258 © 2016 AAPG Eastern Section Meeting, Lexington, Kentucky, September 25-27, 2016