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Abstract: Potential Hydrocarbon Reservoirs and Source Rocks in Cambrian and Ordovician Strata and Their Thermal Maturity, Eastern Kentucky and Adjoining West Virginia

RYDER, R. T., J. E. REPETSKI, and A. G. HARRIS

Recent commercial gas discoveries in Cambrian rocks in eastern Kentucky's Elliott County have renewed exploration activity in the Rome trough. Regional cross sections by the U.S. Geological Survey based on drill holes through the Cambrian and Ordovician sequence in the Rome trough of eastern Kentucky and adjoining West Virginia show potential reservoir and source rocks. Moreover, conodont color alteration indices along or near these cross sections indicate that the thermal maturity of the sequence is favorable for oil and gas.

Possible reservoir units in the sequence are quartzose sandstones in the 1) Middle and Upper Cambrian Maryville Limestone of the Conasauga Group, 2) upper sandstone member of the Upper Cambrian Copper Ridge Dolomite (equivalent to the Rose Run Sandstone), and 3) Middle Ordovician St. Peter Sandstone. The apparent absence of good source rocks (TOC is greater than, or equals to 1) in the Rome trough has diminished its prospects for having large hydrocarbon accumulations. However, the recent commercial gas discoveries are encouraging and suggest that organic-rich strata must exist in the trough. No source for this gas outside the trough is conceivable. Thick Middle Ordovician black shale that is the source for oil and gas in Cambrian and Ordovician rocks in Ohio is absent from this area. Argillaceous carbonate units with black shale interbeds in the Maryville Limestone, shown on the cross sections, may be the source of the gas. Conodont color alteration indices of CAI = 11/2-2 in the Middle Ordovician Black River Limestone and CAI = 2-3 in the Upper Cambrian and Lower Ordovician Knox Group suggest that the thermal maturity is favorable for natural gas and local oil in the Rome trough of eastern Kentucky and adjoining West Virginia.

AAPG Search and Discovery Article #90939©1997 AAPG Eastern Section and TSOP, Lexington, Kentucky