Strontium isotopes as tracers of water co-produced with coalbed natural gas in the Powder River Basin, Wyoming

Coal bed methane production in the Powder River Basin of Wyoming and Montana discharges large volumes of groundwater to the surface daily. There are environmental concerns over the quality and quantity of this produced water. This study uses the 87Sr/86Sr ratio of water co-produced with coal bed natural gas as a fingerprint for coal bed groundwaters and as a tracer of water-rock interactions in an attempt to understand the variations and the controls on Sr isotopic composition of co-produced water extracted from coal seams across the Powder River Basin. The Sr isotopic composition of groundwaters in the basin are influenced by a number of factors including the producing coal zone, groundwater residence time, degree of aquifer confinement, presence of ash, and geographic location. Although the system is complex, this study demonstrates that 87Sr/ 86Sr is a useful and beneficial tool with many industry applications in the Powder River Basin of Wyoming.