Tar-sand deposits in western Kentucky have been recognized as a potentially significant mineral resource since the middle of the nineteenth century. Deposits of bitumen-bearing Late Mississippian and Early Pennsylvanian sandstones have been reported both in surface exposures and in the subsurface for a distance of approximately 100 mi along the southeastern rim of the Eastern Interior basin.
Prior to 1981, published studies of western Kentucky tar-sand deposits had concentrated on the outcrop areas where bitumen-bearing sandstones were present at or near the surface. In-place oil resources were estimated at less than 50 million barrels. Reports that delineated subsurface occurrences of asphaltic sandstones in western Kentucky were not available.
In 1981 the Kentucky Geological Survey initiated a project to inventory and evaluate the oil-resource potential of the asphaltic sandstones in the subsurface of western Kentucky. A preliminary report on the Big Clifty Sandstone (Late Mississippian) was published in 1982.
In 1982 this project was combined with the Interstate Oil Compact Commission’s project by contract with the U. S. Geological Survey to catalog and evaluate the tar-sand resource potential of the United States. Results of investigations by the Kentucky Geological Survey, in conjunction with Lewin and Associates, who were selected to compile the IOCC report, have confirmed that major tar-sand resources are present in western Kentucky. In-place resources are calculated to be in excess of 3 billion barrels.
Past commercial development of tar sands in Kentucky has been restricted largely to use as a paving material. However, because of the ever-expanding demands for energy, these deposits have become the subject of increasing interest as a potential petroleum resource. Three pilot-plant projects are currently recovering heavy oil from tar-sand deposits, and one pilot project is currently in the planning stage.
Figures & Tables
Exploration for Heavy Crude Oil and Natural Bitumen
Gross volumes of oil, which must be kept in mind to address the volume/size framework, may be thought of in order from largest to probably smallest volumes as follows: (1) generated; (2) dissipated; (3) degraded/ partially preserved; and (4) trapped and conventionally producible. Basic knowledge of these volumes may be from greatest to least in essentially reverse order.
The 332 largest known accumulations (less than 1% of the total number) account for more than three-quarters of the known 7.6 trillion bbl of oil and heavy oil or tar in more than 40,000 accumulations in the world. About 2.4 trillion bbl of estimated undiscovered conventional oil added to the known volume of 7.6 trillion bbl yields a total of 10 trillion bbl known or reasonably estimated. World-wide cumulative production of about 500 billion bbl of oil accounts for only 5% of the gross.
Oil in place must be estimated for conventional oil fields before comparison with heavy oil and tar accumulations. The size range of accumulations considered in the size distribution of the 332 largest known accumulations is from 0.8 to 1850 billion bbl of oil. The smallest conventional fields in the distribution are about 1 billion bbl because the size cut-off is 0.5 billion bbl of oil recoverable. The size distribution of the 332 largest known accumulations approaches log normal and is overwhelmed by the largest three supergiant tar deposits that hold nearly half of the total 5495 billion bbl.
Globally, the largest three accumulations, all heavy oil or tar, are in South and North America; the two largest conventional oil fields are in the Middle East. Prudhoe Bay and East Texas fields rank 18 and 34, respectively, in descending size order.