Stable Isotope and Geochemical Investigations into the Hydrogeology and Biogeochemistry of Oil Sands Reservoir Systems in Northeastern Alberta, Canada

Abstract

The objective of this thesis was to provide insight into the hydrogeology and biogeochemistry of the heavily biodegraded bitumen reservoirs of the Athabasca oil sands region of Alberta, Canada, using applications of aqueous and stable isotope geochemistry. Published data were used to generate a regional map of total dissolved solids concentrations in McMurray Formation waters. To explain the regional salinity data, a revised hydrogeological model was developed that incorporates localized upward flow of formation waters from saline Devonian aquifers into the bitumen-bearing McMurray Formation via karst-derived conduits. Where McMurray Formation waters are uninfluenced by connectivity with Devonian aquifers, topographic recharge from meteoric water is the dominant hydrogeological process. A new method was developed to determine the stable isotope composition and salinity of McMurray Formation waters from porewater samples extracted from drilling fluid-contaminated core. Mixing relationships of δ2H and δ18O values in drilling fluid and formation water were used to calculate the original formation water stable isotope composition and salinity from porewater extracted directly from oil sands drill core. Both vertical and lateral heterogeneity were observed on a reservoir-scale, and topographically-derived groundwater recharge was determined to be the dominant hydrogeological process in Suncor-Firebag lease area. Biogeochemical aspects of oil sands systems were investigated in two studies. The first study examined the impact of variable aqueous geochemistry on oil sands biogeochemistry, specifically methanogenesis and bacterial sulfate reduction, in laboratory-scale microcosms. Changes in aqueous geochemistry induced changes in the total amount of methane generated, and in the stable isotope ratios of carbon and hydrogen of generated methane. The second experiment measured natural abundance radiocarbon in dissolved inorganic carbon in a coal-bed methane reservoir in the Powder River Basin, Montana, USA. All samples of dissolved inorganic carbon and methane contained no detectable radiocarbon, and thus the carbon flux from biodegradation of coal was much greater than the carbon flux from recent groundwater recharge into the coal-bed aquifer system. Improved understanding of hydrogeological processes, and better understanding of reservoir biogeochemistry will lead to better decision making by industry and regulators during the development of oil sands resources, while our society transitions away from fossil energy over the coming century.