EVALUATION OF THE CINCINNATI GROUP AS A CAP ROCK FOR THE UTICA SHALE

Recent hydrocarbon exploration in the Utica Shale of Ohio has raised concerns over the impact of hydraulic fracturing on groundwater geochemistry. Uncontrolled propagation of fractures could allow natural gas, brine water, and fracking chemicals to migrate into the overlying fresh water aquifers. An overlying impermeable layer would prevent leakage of hazardous fluids, preserving the integrity of potable groundwater. The lower portion of the Cincinnati Group, dominated by the Ordovician calcareous shale that overlies the Utica throughout the Midwest region, may provide the impermeable layer needed to prevent upward leakage of hydrocarbons and hydraulic fracturing fluids.

This assessment includes evaluation of lithology, thickness, permeability, ductility, elasticity, and fracture gradient of the lower Cincinnati Group to determine its effectiveness as a cap rock. Well logs and Ohio Geological Survey maps will provide depth and thickness information. Mineralogy will be investigated with powder X-ray diffraction and polarized light microscopy, for the purpose of assessing the relationship between lithology, cementation, and permeability. Probe and pulse decay gas permeametry will provide permeability measurements necessary to determine the resistance to fluid flow through the rocks. Lastly, geomechanical parameters (ductility, elasticity, and fracture gradient) determined from rock-strength testing will give insight into the formation’s response to stress, and therefore help us predict the conditions necessary to produce fractures.

Preliminary pulse decay permeametry results show an average horizontal permeability of .145 mD, and an average vertical permeability of .082 mD. Further analysis using the other methods is in progress.

This research is a joint effort between Ohio Department of Natural Resources (ODNR), and Subsurface Energy Materials Characterization and Analysis Lab (SEMCAL) at the school of Earth Sciences at The Ohio State University.