Delineating Subsurface Structural Trends in Ohio via Mapping
The Ohio Geological Survey is conducting projects to appraise Ohio’s geologic resources as they apply to developing shale oil and gas, storing CO2, and assessing geothermal potential. The research addresses specific project objectives for the Ohio Coal Development Office (OCDO) and the National Geothermal Data System (NGDS), the latter project funded by the U.S. Department of Energy (DOE).
The initial goal of the OCDO project is to evaluate geologic conditions favorable for CO2 storage in eastern Ohio. This includes detailed mapping of subsurface horizons with high data density to ascertain structural trends concurrent at multiple horizons. Horizon elevations interpreted by staff geologists are combined with driller-reported horizon elevations. The combined dataset is statically evaluated; deference is given to geologists’ interpretations. Once local outliers are removed, the dataset is contoured using kriging. Separate contour maps are created for areas where data density is low. These contours are then manually spliced together. Currently mapped, greater-detailed surfaces include the Upper Ordovician Queenston Shale, the Wenlockian Dayton Formation, the Middle Devonian Onondaga Limestone, and the Upper Devonian Berea Sandstone. From this mapping, northwest–southeast structural trends are evident in Wayne, Medina, Knox, and Tuscarawas Counties, and a west–east structural trend is visible in Tuscarawas County.
The American Association of State Geologists administers a DOE grant to the states to provide geothermal data that can be accessed via the NGDS. To date, 480 Ohio bottom-hole temperature (BHT) observations have been corrected and mapped, and their gradients were also estimated and mapped. Using the corrected BHT data, the temperatures and thermal gradients are gridded and contoured using kriging. Wells in excess of 10,000 feet are drilled in the Appalachian Basin of eastern Ohio, where virgin rock temperature can approach 100°C, which is suitable for space heating and possible co-production of electricity by rankine-cycle generators. The critical point of CO2 is temperature dependent; thus these maps are also useful to find subsurface conditions favorable for CO2 storage. Future CO2 sequestration may involve CO2 as a working fluid in geothermal energy capture as well as enhancing recovery of oil and gas. These new energy technologies have the potential of extending the utility of many existing oil-and-gas wells.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012