Extraction of radioactive and toxic element contaminants from organic-rich shale in contact with hydraulic fracturing fluids

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CBET 1336719Ellis, Brian R.University of Michigan Ann ArborRecent advances in directional drilling and well stimulation techniques 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 fracturing fluids that flow back to the surface, which must be properly handled to avoid contamination of fresh water resources. The primary objective of this study is to characterize the interactions between the hydraulic fracturing fluid and organic-rich shales in order to determine the potential for hydraulic fracturing fluid chemicals to mobilize undesirable trace toxic metal and radionuclide flowback fluid constituents. While flowback fluids are expected to be contaminated to some degree, e.g., it is known that these fluids may be highly saline and contain elevated levels of trace toxic metals and radioactive elements, the potential for these contaminants to be leached as a function of the shale composition, down-hole conditions, and chemical additives present in hydraulic fracturing fluid formulations has not yet been determined. To address this knowledge gap, a series of batch and flow-through experiments will be performed to assess the impact of these parameters on contaminant leaching. Experiments will be conducted on natural shale rock samples from two Michigan shale gas reservoirs, under typical in situ temperature and pressure conditions encountered in the field. Unique and state-of-the art high temperature and pressure apparatuses will be constructed for this research and used to development standardized methods for evaluating the chemical processes and mechanisms controlling the release of inorganic toxic and radioactive elements from organic-rich shales in contact with hydraulic fracturing fluids in the subsurface.Current efforts to assess flowback water quality rely on the analysis of the water once it has returned to the surface. To properly address or dismiss concerns regarding water quality impacts associated with hydraulic fracturing, a better understanding of the chemical evolution of hydraulic fracturing fluids in the subsurface is required. The results of this study will help guide industry best practices for sustainably developing domestic shale gas resources and for reducing potential water quality impacts associated with hydraulic fracturing well completions. Furthermore, understanding the chemical evolution of the injected fluids will aid in forming sound regulatory policy addressing flowback water management practices, including treatment, reuse and disposal.