Recent advances in directional drilling have made extraction of natural gas and oil from shale formations economically viable via high-volume hydraulic fracturing. A side effect of hydraulic fracturing is the exposure of previously hydraulically isolated minerals that may contain naturally occurring radioactive material and toxic metal elements. These constituents may be released into the fracking flowback water returning to the surface, which must be properly handled to avoid contamination of fresh water resources. To properly address or dismiss the concerns regarding water quality impacts associated with hydraulic fracturing, a better understanding of the chemical evolution of fracking fluids in the subsurface is required. The primary objective of this study is to characterize the interactions between the hydraulic fracturing fluid and organic-rich shales, in order to assess the potential for fracking fluid chemicals to mobilize undesirable trace toxic metal and radionuclide flowback fluid constituents. This presentation will focus on the two primary shale-gas reservoirs within the Michigan basin, the Antrim and the Utica-Collingwood shales. A novel batch reactor apparatus is used to bring model hydraulic fracturing fluid mixtures into contact with shale samples under in situ temperatures and pressures conditions, mimicking the subsurface environment, to elucidate the key parameters (T, P, pH, pe, chemical additives) controlling the rate and extent of leaching of trace contaminants of concern. Preliminary results from these batch reactor studies will be presented alongside spectroscopic analysis of the changes in shale mineralogy after contact with the hydraulic fracturing fluids. Geochemical characterization of these two unconventional reservoirs will also include analysis of bulk toxic metal and radionuclide content and assessments of maximum leachate contributions to the flowback water contaminant levels.

Geochemical investigations of Michigan basin organic-rich shales in contact with hydraulic fracturing fluids

246th National Meeting (2013)

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