T149 The Water-Energy Nexus in Sedimentary Basins

Wednesday, 28 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

A CRITICAL EVALUATION OF STRONTIUM ISOTOPES AS A TRACER OF POSSIBLE BRINE CONTAMINATION IN SHALLOW AQUIFERS RELATED TO OIL/GAS PRODUCTION

Paper number: T149-9
Program: Technical Sessions
Time: 3:20 PM – 3:35 PM

Authors

Abstract

Both unconventional and conventional oil/gas production have led to instances of brine contamination of near-surface environments from saline produced waters spills. Strontium isotope ratios (87Sr/86Sr) have been used as a sensitive tracer of brine contamination sources in streams and shallow aquifers in areas where oil/gas production are limited to only a few reservoirs and produced water sources are well-defined. Recent expansion of unconventional oil/gas production to additional tight formations within sedimentary basins has resulted in production of formation waters from multiple oil/gas reservoirs that may have similar chemical and isotopic ratios, including 87Sr/86Sr ratios. This study critically evaluates the utility of 87Sr/86Sr ratios as a tracer of brine contamination related to conventional and unconventional oil/gas production in two major hydrocarbon provinces: the Williston and Appalachian basins in North America. Multiple stacked oil/gas reservoirs within each basin have overlapping 87Sr/86Sr ratios of formation waters based on a non-parametric statistical test. For example, in the Appalachian Basin, produced waters from unconventional gas production in the Middle Devonian Marcellus and Upper Ordovician Utica shales have overlapping 87Sr/86Sr ratios. Sr-isotopes alone may not be a useful tracer of saline produced water contamination in regions with both Marcellus and Utica shale oil/gas and associated saline formation water production. Likewise, in the Williston Basin, produced waters from unconventional oil production in the Late Devonian to Early Mississippian Bakken Formation have overlapping 87Sr/86Sr ratios with conventional oil production from the Middle Devonian Winnipegosis and the Mississippian Madison groups. In addition, there is significant spatial variability in 87Sr/86Sr ratios of formation waters across the basins likely from changes in lithology. Improved spatial distribution of 87Sr/86Sr ratios and other isotopic ratios of produced waters are needed to constrain geographic variability in hydrocarbon producing regions. As unconventional oil/gas production expands to include additional reservoirs and in areas of existing conventional oil/gas production, multiple isotopic tracers will be required to delineate the saline produced water sources.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-356740

© Copyright 2020 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.