Geochemistry and Thermal Maturation of the Ordovician Utica Shale in the Redstone Corporation No. 3 Barth Well, Coshocton County, Ohio: ABSTRACT

Abstract

The Middle and Upper Ordovician Utica Shale is an important petroleum source rock in the central Appalachian basin. We analyzed a continuous core of the Utica Shale between 5630 and 5749 ft in the Redstone No. 3 Barth well, Coshocton County, Ohio, to geochemically characterize the Utica in a region of relatively low thermal maturity. Rock-Eval analyses of ten black shale samples, yielding average TOC = 3.1%, Tmax = 440{degrees}C, and Pl = 0.27, indicate that the Utica Shale in Coshocton County is a very good petroleum source rock that has reached the beginning to middle part of the oil-generation stage. Conodont alteration index (CAl) values of 1 to 1.5 from conodonts in thin calcareous beds in the Utica Shale support the Rock-Eval data. Average Hl = 174 mgHC/g C{sub org} and OL = 76 mgCO{sub 2}/g C{sub org} indicate a predominance of Type II organic matter in the Utica. Bitumen was extracted from four Utica shale samples (5,200 to 6,000 ppm) and analyzed by gas chromoatography (GC) and GC-mass spectrometry. Gas chromatograms show a slight-odd-predominance of the n-C{sub 11} to n-C{sub 17} fraction, a broad spectrum of n-alkanes that range from n-C{sub 7} to n-C{sub 33}, and abundant pristanemore » and phytane. Mass fragmentograms of biomarker compounds reveal abundant terpane (191 m/z) and sterane (217 m/z) compounds and few pentacyclic (191 m/z) compounds. Except for the low concentration of pentacyclics, the bitumen extracts are very similar geochemically to oils produced from Cambrian and Lower Ordovician reservoirs in eastern and central Ohio. Maturation kinetics models indicate that the Utica Shale in the core reached the oil-generation stage during Pennsylvanian time.« less