Department of Hydrology and Atmospheric Sciences,The University of Arizona, Tucson, Arizona
Several recent studies have suggested that strontium isotopes, combined with water stable isotopes and ion chemistry (including bromide) are useful to determine rock-water interaction, subsurface fluid migration pathways, and sources of brine contamination in shallow aquifers. Strontium isotopes do not fractionate in nature and fluids retain the 87Sr/86Sr ratio of the aquifer or confining unit materials that they have interacted with in the subsurface. Therefore, Sr isotopes can provide information about rock-water interaction along flow paths from depth into the Critical Zone or mixing of formation waters between reservoirs, and thus compartmentalization of fluids in subsurface formations.
This study has two main goals: 1) to synthesize existing data and evaluate if Sr isotopes are indeed an optimum tracer for brine contamination in shallow aquifers; and 2) to apply Sr isotopes in a case study to trace the sources of high salinity measured in the shallow aquifers overlying the Raudhatain oil field, one of the largest in Kuwait. For the first part of the study, we are planning to compile all available strontium isotopes, major ion chemistry data (including bromide), and water stable isotopes from four major sedimentary basins in the United States: Williston, Appalachian, Permian, and Illinois basins. Specifically, we will evaluate how unique Sr isotope signatures are between fluids in hydrocarbon-bearing formations to determine if Sr isotopes can be used as a tracer of brine contamination from specific oil/gas reservoirs.
Kuwait Oil Company plans to drill more oil wells in the Raudhatain oil field each year for the foreseeable future to increase oil and gas production. Previous studies in other areas have reported higher numbers of accidental brine spills due to infrastructure failures in areas with high number of oil/gas wells. Brine contamination in shallow aquifers can also come from re-injection of seawater or produced brine to maintain reservoir pressures, contamination due to infiltration of brines stored in surface, and/or the natural upward movement of deep formation water. In this study 87Sr/86Sr ratios of shallow saline aquifers and the different sources of possible contamination in the Ruadhatain area will be measured. If the different sources of contamination and the shallow aquifers have a distinctive 87Sr/86Sr ratio then we can fingerprint the source and origin of contamination in the shallow aquifer.