Ordovician Dolostones in Central Kentucky: Possible Analogs for Trenton–Black River Gas Reservoirs in the Appalachian Basin

By

HARRIS, DAVID C.

Kentucky Geological Survey, Lexington, KY,

LANGHORNE “TAURY” SMITH

Center for Stratigraphy and Paleontology, New York State Museum, Albany, NY

     The occurrence of discrete dolostone bodies in Upper and Middle Ordovician limestone strata of central Kentucky has been well documented by geologic mapping done in the 1970’s. These dolostone outcrops are spatially related to mapped faults, and have been interpreted as products of hydrothermal fluids that moved along fault conduits, replacing adjacent limestone. There is new economic interest in fault-controlled dolomitization as the result of significant natural gas discoveries in the Ordovician Trenton–Black River Formations in central New York. Gas production from these formations is attributed to dolostone reservoirs localized along faults.

     With funding from the New York Energy Research and Development Authority, U.S. Department. of Energy, and Triana Energy, the Kentucky Geological Survey and New York State Museum are studying the central Kentucky outcrops in a 2-year project to provide an analog for similar reservoirs in the Appalachian Basin. Goals of this work include interpreting the timing, structural control, and origin of dolostones, and their relationship to hydrocarbons. Field work has documented stratigraphic controls on replacement of limestone by dolomite. Petrographic work will provide data on the diagenetic sequence and relative timing of dolomitization. Boreholes will be drilled to core two of the larger dolostone bodies, to better characterize their three-dimensional geometry and vertical variability. Geochemical work in progress on the dolostones includes trace element, stable isotope, and fluid inclusion analyses to help constrain a dolomitization model.

     Results from the well-exposed outcrops in Kentucky will be linked to cores, logs, cuttings, and production data from active Trenton-Black River fields in New York. The knowledge gained from the outcrops in Kentucky should lead to a better understanding of these complex reservoirs in New York and throughout eastern North America.

     Using the Economics of Environmental Efficiency to Conduct Cost-Effective