GEOCHEMISTRY AND STABLE ISOTOPIC SIGNATURES, INCLUDING CHLORINE ISOTOPES OF THE WILLISTON BASIN, CANADA

Formation waters from three profiles of the Williston Basin were examined for geochemistry and stable isotopes (²H, ¹⁸O, ³⁷Cl). Sample depths ranged from 300 to 3700 meters. The research goals focused on using stable isotope data to better understand the origin of the formation waters of the basin and to observe the influence of mixing and other chemical processes associated with the evolution of groundwaters. The samples showed large variations in d¹⁸O signatures, ranging from –17 ‰ to +12 ‰. This variation did not correlate with depth. The d²H of these samples showed a large spread, ranging from –130 ‰ to almost 0 ‰. The d³⁷Cl signatures ranged between –1.0 ‰ and +1.0 ‰ with slightly more depleted signatures of fluids with higher Cl concentrations. Most samples showed high concentrations of Br and the ratios of Br/Cl ranged between 0.001 and 0.008. The relationship between the log Cl vs. log Br of these samples showed that they follow a seawater concentration trend. Research is ongoing to recognize the sources of these formation waters and the impact of various chemical and physical processes by using different isotopic methods in combination with these geochemical results.