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

R. T. Ryder, R. C. Burruss, J. R. Hatch, J. D. King, V. F. Nuccio, G. A. Schumacher, A. G. Harris

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°C, and PI = 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 (CAI) values of 1 to 1.5 from conodonts in thin calcareous beds in the Utica Shale support the Rock-Eval data. Average HI = 174 mgHC/g C_org and OI = 76 mgCO₂/g C_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 chromatography (GC) an GC-mass spectrometry. Gas chromatograms show a slight odd-predominance of the n-C₁₁ to n-C₁₇ fraction, a broad spectrum of n-alkanes that range from n-C₇ to n-C₃₃, and abundant pristane 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-generat on stage during Pennsylvanian time.

AAPG Search and Discovery Article #90954©1995 AAPG Eastern Section, Schenectady, New York