Evaluating Naturally Occurring Radioactive Materials in Michigan Basin Shale Gas Produced Fluids.

The growth in unconventional natural gas production across the U.S. has resulted in the need to dispose of large volumes of shale gas produced brine. Organic-rich shales maintain reducing environments in the subsurface that can lead to immobilization and subsequent concentration of naturally occurring U within U(IV) minerals. Produced brines and flowback fluids from these formations subsequently also contain elevated levels of naturally occurring radioactive materials (NORM), such as ²²⁶Ra and ²²⁸Ra. This enhanced degree of radioactivity in shale formation fluids can present new disposal/handling challenges to operators, which is exacerbated by the rapid expansion in shale gas production wells and the need to handle large volumes of these produced fluids. This presentation will discuss the historic and emerging shale gas plays in the Michigan Basin and ongoing efforts at the University of Michigan to characterize produced fluids from these shale plays. Results from laboratory experiments examining the impact of various chemical additives in mobilizing U from shales will be presented. Batch and flow-through experimental apparatuses are utilized to characterize shale-fluid interactions and study the evolution of fluid chemistry under relevant reservoir temperatures and pressures. Fluid characterization includes analysis of major cations and anions via ICP-MS and IC, respectively. Gamma ray spectrometry is used to determine ²²⁶Ra and ²²⁸Ra activities in the effluent fluids. Characterization of field samples collected from producing wells in the Antrim shale will also be presented. Studying the impact of hydraulic fracturing fluid chemical additives on the leaching of radionuclides from shale gas formations is an important step toward improving our understanding of NORM in shale gas produced fluids. The low level radioactivity of these fluids may ultimately be a controlling factor in choosing appropriate treatment and disposal options.