A MULTI-ISOTOPE APPROACH TO STUDYING THE SOURCE, ORIGIN, AND HISTORY OF PRODUCED WATERS FROM SHALE RESERVOIRS: EXAMPLES FROM THE PERMIAN AND GULF COAST BASINS

Since the advent of oil and gas production from low permeability reservoirs, data from reservoir characterization, petrophysics, and fluid dynamics have gleaned new insight into the behavior of these systems and raised questions about our understanding of processes in tight systems. Although, typically considered a waste product, investigations of produced waters from these same systems have led to insights as well. While compositional data for produced waters have been used and interpreted by oil and gas producers for decades, application of corresponding isotope geochemistry has lagged. This presentation provides background on the practical use of stable (δ¹¹B, δ²H, δ¹⁸O) and radiogenic isotope (²²⁸Ra/²²⁶Ra, and ⁸⁷Sr/⁸⁶Sr) systems in the study of produced waters from the Wolfcamp and “Cline” shales in the Permian Basin and the lower Eagle Ford Shale in the Gulf Coast Basin. Results help determine whether the produced water is generated within the formation or originated from adjacent formations and provide constraints on the timing in which the produced water entered the formation relative to clay diagenesis and hydrocarbon maturation. Findings also indicate the extent to which hydrodynamic redistribution of the hydrocarbons and water in the reservoir has occurred. The ability to use multiple isotopes as fingerprinting tools in environmental investigations will also be discussed. This effort will demonstrate that significant insight can be provided to oil and gas operators and stakeholders through a multiple isotope approach.