BLACK SHALE SOURCE ROCKS AND OIL GENERATION IN THE CAMBRIAN AND ORDOVICIAN OF THE CENTRAL APPALACHIAN BASIN, USA

Nearly 600 million bbl of oil (MMBO) and 1 to 1.5 trillion ft(3) (tcf) Of gas have been produced from Cambrian and Ordovician reservoirs (ca rbonate and sandstone) in the Ohio part of the Appalachian basin and o n adjoining arches in Ohio, Indiana, and Ontario, Canada, Most of the oil and gas is concentrated in the giant Lima-Indiana field on the Fin dlay and Kankakee arches and in small fields distributed along the Kno x unconformity. Based on new geochemical analyses of oils, potential s ource rocks, bitumen extracts, and previously published geochemical da ta, we conclude that the oils in both groups of fields originated from Middle and Upper Ordovician black shale (Utica and Antes shales) in t he Appalachian basin, Moreover, we suggest that approximately 300 MMBO and many trillions of cubic feet of gas in the Lon er Silurian Clinto n sands of eastern Ohio originated in these same source rocks. Oils fr om the Cambrian and Ordovician reservoirs have similar saturated hydro carbon compositions, biomarker distributions, and carbon isotope signa tures, Regional variations in the oils are attributed to differences i n thermal maturation rather than to differences in source, Total organ ic carbon content, genetic potential, regional extent, and bitumen ext ract geochemistry identify the black shale of the Utica and Antes shal es as the most plausible source of the ails, Other Cambrian and Ordovi cian shale and carbonate units, such as the Wells Creek formation, whi ch rests on the Knox unconformity, and the Rome Formation and Conasaug a Group in tile Rsme trough, are considered to be only local petroleum sources, T-max, CAI, and pyrolysis yields from drill-hole cuttings an d core indicate that the Urica Shale in eastern and central Ohio is ma ture with respect to oil generation, Burial, thermal, and hydrocarbon- generation history models suggest that much of the oil was generated f rom the Utica-Antes source in the late Paleozoic during the Alleghania n orogeny. A pervasive fracture network controlled by basement tectoni cs aided in the distribution of oil from the source to the trap, This fracture network permitted oil to move laterally and stratigraphically downsection through eastward-dipping, impermeable carbonate sequences to carrier zones such as the Middle Ordovician Knox unconformity, and to reservoirs such as porous dolomite in the Middle Ordovician Trento n Limestone in the Lima-Indiana field, Some of the oil and gas from th e Utica-Antes source escaped vertically through a partially fractured, leaky Upper Ordovician shale seal into widespread Lower Silurian sand stone reservoirs.