Abstract

The Appalachian basin has had a long history of oil and gas production from fractured Ordovician carbonate reservoirs. In 1829 the first gusher of record in North America, the "American Oil Well" was drilled in Cumberland County, Kentucky. This well produced both gas and oil from fractured Middle Ordovician carbonates. Commercial production of gas from the Middle Ordovician Trenton Limestone began in 1884 in northwestern Ohio near the city of Findlay in Hancock County. Discoveries from this interval continue into the present and should provide much-needed hydrocarbons for the future as explorationists venture deeper into the Appalachian Basin.

Porosity development along faults and fractures characterize the Middle Ordovician fractured carbonate play. Reservoirs of this play are found associated predominantly with large structural features. Fields of this play have been identified along the faulted northwestern and western margin of the Appalachian basin (particularly south-central Ontario, northwestern through central-eastern Ohio, north- central Tennessee, central Kentucky), in eastern Kentucky within the Rome trough, and in western Virginia associated with the Pine Mountain fault system. Much of the fracturing associated with these reservoirs is thought to be due to reactivation of deeper structures. Porosity development/enhancement of these reservoirs occurs as a result of fluids circulating along these faults and fractures.

Because so many of the fields of this play were produced in the late 1800s and early 1900s it is difficult to obtain reliable production figures. However, using the available figures yields an estimated original gas reserve of 52 Bcf and an original gas in place of 65 Bcf for this play in the Appalachian Basin. These amounts are only for proven areas. Large, potentially productive areas of the basin remain untested for gas and oil from the Middle Ordovician Carbonates.