Organic Carbon Isotope Records of Cores from The Oatka Creek Member of The Marcellus Formation - Pennsylvania, United States

Open Access
Author:
Can, Cihan
Graduate Program:
Petroleum and Natural Gas Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 02, 2014
Committee Members:
  • Dr Li Li, Thesis Advisor
  • Michael Allan Arthur, Thesis Advisor
Keywords:
  • Stable isotopes
  • Total organic carbon
  • Geochemistry
  • Bald Eagle Core
  • Bilger Core
  • Kačák-Otomari bioevent
  • Natural gas potential
Abstract:
Gas from shales is growing in importance with the development of technology that allows improved natural gas production. Devonian shales from the Appalachian Basin are recognized for their significant natural gas potential. The Marcellus Shale Formation is the lowest unit of the Devonian age from Hamilton Group and consists primarily of black shales high in organic carbon. Subunits of The Marcellus Formation have been studied to assess the abundance of the organic matter and type in the shale. The Oatka Creek Member of the Marcellus Formation was chosen for this study because of its high gamma ray log response, which corresponds to increased Uranium content, and the presence of organic carbon enrichment. Few data are available on this unit because much of the focus has been on the lower part of the Marcellus Formation (The Union Springs Member). Additionally, the distinct Kačák-Otomari bioevent is thought to have had a big influence on black shale deposition globally within the interval of Oatka Creek Member's deposition. For this study, The Bald Eagle and Bilger cores of the Oatka Creek Member were analyzed to assess the effect of The Kačák-Otomari event on sedimentation in the Appalachian Basin, and to examine the organic carbon content and the sources that affected the organic carbon deposition in the cores. Total organic carbon (TOC) content and carbon stable isotopic values of The Bald Eagle and Bilger cores from Pennsylvania were determined after crushing and decarbonation steps. Based on these analyses, TOC content in the Bald Eagle Oatka Creek Member (692 to 780 ft) varies between 1.19 and 4.65 %, whereas the TOC content of the Bilger Oatka Creek Member (160 to 250 ft) varies between 0.21 and 2.8 %. The δ13Corg values in the Bald Eagle core have a narrow range of -29.1 to -29.9 ‰ (PDB) whereas the δ13Corg values for the Bilger core have a relatively wider range of -25.6 to -29.9 ‰ (PDB). The organic carbon content in the Bald Eagle core is much higher than that in the Bilger core, and the lithofacies of the Oatka Creek Member suggest less overall dilution and/or oxygenation at the location of the Bald Eagle core. Kačák-Otomari bioevent didn't have much influence in both of the cores because of the lack of significant isotopic trend excursions. Because the δ13Corg pattern of Bald Eagle core is uniform and depleted in BC, this study suggests the dominance of amorphous marine organic matter at that location whereas in Bilger core marine organic matter gives way upward to increasing terrestrial organic matter input indicated by the trend towards more enriched δ13Corg values. This study establishes a base line for the organic carbon content and stable isotopic trends of the Bald Eagle and the Bilger cores. The comparison between these two cores helps interpretations for the general characteristics of the cores and the organic carbon enrichment throughout the whole zone.