Geophysical assessment of the Cincinnati Group as a cap rock
The Ohio State University, Columbus, OH, [email protected]
Recent hydrocarbon exploration of the Utica Shale in Ohio has raised concerns over the impact of hydraulic fracturing on ground water geochemistry. Uncontrolled propagation of fractures could allow natural gas, brine water, and fracking chemicals to migrate upward into near-surface fresh water aquifers. An overlying impermeable layer would prevent leakage of hazardous fluids, preserving the integrity of potable ground water. A proven cap rock could also potentially serve to contain sequestered CO2. 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 leakage of hydrocarbons and other fluids. Thus, the viability of the Cincinnati Group as a cap rock will be investigated via laboratory and geophysical methods.
This assessment will include laboratory evaluation of lithology, porosity, permeability, ductility, elasticity, and fracture gradient, as well as investigation of seismic and well log data from the Cincinnati Group. Well logs and Ohio Geological Survey maps will provide the depth, thickness, and aerial extent of the formation. Mineralogy will be investigated via powder X-ray diffraction and SEM analysis, for the purpose of assessing the relationship between lithology, cementation, and permeability. Porosity will be investigated through Hg porosimetry and BET analysis. 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 help predict the conditions necessary to produce fractures.
The aim of this study is to assess the viability of the Cincinnati Group to serve as a cap rock for both CO2 sequestration and for containing hazardous fluids associated with hydrocarbon exploration.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012