HIGH-RESOLUTION CYCLOSTRATIGRAPHY OF THE LOWER HURON MEMBER OF THE OHIO SHALE THROUGHOUT CENTRAL AND EASTERN OHIO

The Ohio Department of Natural Resources, Division of Geological Survey (Ohio Geological Survey) is involved in the collaborative, multistate Midwest Regional Carbon Sequestration Partnership project funded by the Department of Energy to evaluate the utility of strata in the Appalachian Basin for carbon utilization and sequestration. The organic-rich Upper Devonian shale sequence of the northwestern Appalachian Basin holds potential for both carbon sequestration and enhanced natural gas recovery via high-pressure injection of CO₂. Previous studies (e.g., the Eastern Gas Shales Project) provided valuable general information regarding total organic carbon and thermal maturity of the Devonian shale interval in Ohio. However, the data rarely were tied to a stratigraphic framework with resolution high enough for precise resource characterization necessary for unconventional development. The Ohio Geological Survey currently is working to subdivide the Devonian shale sequence into a high-resolution, cyclostratigraphic framework that will allow precise characterization of the hydrocarbon production and carbon sequestration potential of the numerous shale units of this interval. The organic-rich lower Huron Member of the Ohio Shale consists of stacked black and gray shales, making it ideal for cyclostratigraphic interpretation and correlation based on geophysical logs. Eight cycles were picked based on gamma-ray and bulk-density curves and correlated in 541 logs from wells throughout central and eastern Ohio. Isopach maps for each of the cycles were created using Petra^® and ArcGIS^® software. Thickness variations from cycle to cycle indicate that movement along basement-penetrating faults controlled localized zones of increased subsidence during the deposition of the lower Huron Member. Additionally, overall depositional strike changed from trending N–S to NNE–SSW after the deposition of cycle four in the lower Huron Member. This study highlights the utility of high-resolution stratigraphy for analysis of localized basin subsidence and provides a first step towards greater understanding of the geologic controls of high-quality source rock deposition and preservation.