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Water produced with coalbed natural gas (CBNG) attains its characteristic sodium-bicarbonate composition through a series of processes, including dissolution of salts, precipitation of salts, pyrite oxidation, ion exchange, sulfate reduction, and methanogenesis. After CBNG-produced water is discharged to the surface, interaction with the atmosphere will initiate the precipitation of calcite, iron hydroxide, and barite among other minerals. The interaction of CBNG-produced waters with semiarid Powder River Basin soils can mobilize accumulated salts, which, through infiltration, can then reach the water table, potentially affecting the quality of the groundwater. The mobilization of the soil-based salts may render the composition of the water recharging the near-surface groundwater very different from the initial chemical composition of the CBNG-produced water. Additionally, prolonged exposure to CBNG-produced water can cause the salinization and sodification of soils surrounding CBNG-produced water ponds and streams carrying CBNG-produced water. This can impact the quantity of biomass and the species composition of the vegetation in proximity to CBNG-produced water discharge locations. The high sodium to calcium and magnesium ratio in CBNG-produced water requires careful management to prevent sodification of irrigated soils when it is used as an irrigation source. In many instances, irrigation with CBNG-produced water requires the addition of soil amendments such as gypsum and sulfur to maintain the fertility and physical qualities of the soil. An understanding of the geochemical evolution of CBNG-produced water is necessary to anticipate and address these potential environmental issues associated with production of CBNG.
Elizabeth Brinck received her Ph.D. in geology from the University of Wyoming. Her dissertation work included groundwater and soil chemistry changes associated with coalbed methane development. Since completing her degree in 2007, she has been employed by the Montana Bureau of Mines and Geology to research groundwater quality and quantity issues in eastern Montana.
James Drever graduated from Princeton University with a Ph.D. in geochemistry. He served on the faculty of the University of Wyoming until retirement in 2005. He is a past president of the Geochemical Society and the author of the textbook The Geochemistry of Natural Waters. He has written numerous articles on the geochemistry of surface and groundwaters.
Carol Frost graduated with a Ph.D. in earth sciences from the University of Cambridge. She is a professor of geology and the Associate Vice President for Research and Economic Development at the University of Wyoming. Her research interests involve the application of isotopic tracers to varied problems from the origin and evolution of the continental crust to the geochemistry of water coproduced with coalbed methane.