A critical evaluation of Strontium Isotopes as a tracer of fluids in subsurface reservoirs and possible brine contamination in shallow aquifers related to oil/gas production

Mohammad Marza, Aidan Mowat2, Keegan Jellicoe3, Grant Ferguson1,3 and Jennifer McIntosh
Department of Hydrology and Atmospheric Sciences
The University of Arizona

Both unconventional and conventional oil/gas production have led to instances of brine contamination of near-surface environments from spills of flowback and produced waters. Strontium isotopes (87Sr/86Sr) have been used as a tracer of sources of brine contamination in surface waters or shallow   aquifers in areas with limited brine sources. Expansion of unconventional oil and gas production has resulted in produced waters from multiple geologic formations that may have similar 87Sr/86Sr, making it unclear if Sr isotopes are an adequate tracer for brine contamination. This study evaluated the utility of 87Sr/86Sras a tracer of brine contamination in shallow aquifers related to oil/gas production. Strontium isotopes of formation waters were investigated for two major oil and gas producing regions in the United States: the Williston (WB) and Appalachian (AB) basins. Multiple formations with depth in the two basins have overlapping 87Sr/86Srof formation waters based on a non-parametric statistical test (e.g. the Middle Devonian Marcellus and Upper Ordovician Utica shales in the AB). In addition, there is significant spatial-variability in 87Sr/86Srof formation waters across the basins hypothesized to be from changes in lithology. More spatially distributed fluid Sr isotope data are needed to constrain geographic variability in hydrocarbon producing regions.

1Designated Campus Colleague, Department of Hydrology and Atmospheric Sciences, University of Arizona
2Department of Civil, Geological and Environmental Engineering, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
3Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

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