CORRELATION OF MIDDLE AND UPPER DEVONIAN SHALES IN THE MARCELLUS-PRODUCING REGIONS OF PENNSYLVANIA

The Eastern Gas Shales Project (EGSP) of the 1970s-80s was the first concerted multi-state effort to evaluate the natural gas potential of Devonian and Mississippian organic-rich black shales of the Appalachian, Illinois, and Michigan basins. As a member of the EGSP research consortium, the Pennsylvania Geological Survey (PaGS) established a basic subsurface stratigraphy of the Middle and Upper Devonian section in Pennsylvania using gamma-ray wireline logs, and constructed structure, isopach, and isolith maps of the Upper Devonian Canadaway, Java, West Falls, Sonyea, and Genesee formations, and the Middle Devonian Hamilton Group, which includes the Marcellus shale at its base. With respect to the Marcellus, PaGS made no distinction between the actual Marcellus and any other formation within the Hamilton Group. As a result, the “Marcellus facies” included shales from the overlying Skaneateles, Ludlowville, and Moscow formations. In fact, it was the organic-rich shales of this “Marcellus facies” that produced gas in Range Resources LLC’s #1 Renz well, the discovery well of the modern Marcellus play in the Appalachian basin. Since 2004, thousands of shale gas wells have been drilled in Pennsylvania alone, generating renewed interest in the lithostratigraphy, mineralogy, and thermal maturity of the Marcellus and other organic-rich shales. The modern downhole geophysical log data associated with these shale gas completions has facilitated a deeper dive into the lithostratigraphy of both the Marcellus Formation and shallower Middle and Upper Devonian shales. As part of PaGS’s ongoing geologic carbon capture and storage research – namely, interpreting and mapping the lithostratigraphy of organic-rich shales for enhanced gas recovery potential using carbon dioxide – we have built on EGSP and subsequent work to refine the lithostratigraphy of the Hamilton Group and other Devonian shale formations mapped previously. PaGS has interpreted additional geophysical logs, especially gamma-ray and density where available, and related data for ~3,500 wells in 41 counties to resolve Devonian shale interpretations to the formation and/or member level. Here we present new cross sections showing our reinterpreted stratigraphy for the western and northern portions of the state using these data.