GEOCHEMICAL PERSPECTIVES ON TREATMENT AND REUSE OF PRODUCED WATER FROM HYDRAULICALLY STIMULATED NIOBRARA FORMATION PETROLEUM WELLS

Hydrocarbon production also generates so-called produced water (i.e., a mixture of returned injection fluids and geologic formation brines) which represents the largest volumetric waste stream associated with hydrocarbon recovery in the United States. As such, produced water has been the focus of intense study with emphasis on understanding the environmental impacts of unintended or intentional release, disposal concerns, commodity (e.g., lithium) potential, and the geologic origin of the fluids. Here we present the major ion geochemistry, radium activities, and stable water isotope composition (δ²H and δ¹⁸O) of ~120 produced water samples collected from 17 petroleum wells producing from the Late Cretaceous Niobrara Formation, Weld County, Colorado. The sample set encompasses eight produced water time series from four newly completed wells across production days 0 to ~365 and from four established wells across production days ~1000 to ~1700, as well as produced water from nine other established wells sampled at discrete time points ranging from day 458 to day 2256. These results significantly expand the available Niobrara Formation produced water geochemical data which was previously limited to one to two wells sampled within the first year of production. The expanded dataset allows for fluid geochemical heterogeneity in both time and space to be evaluated. Furthermore, this study helps to constrain the origin of salinity in Niobrara Formation brines from the Denver-Julesburg Basin by evaluating geochemical relationships between major ion ratios and stable water isotope composition. Our findings are discussed with perspective toward treatment options and potential reuse of produced water from the Niobrara Formation prior to disposal.