Origin and Li-Enrichment of Selected Oilfield Brines in the Alberta Basin, Canada

Oilfield brines investigated in this study occupy both the pre-Cretaceous and post-Jurassic regional groundwater flow regimes within the Alberta Basin. Samples of pre-Cretaceous groundwater primarily represent Devonian carbonate units while post-Jurassic regime samples primarily represent Cretaceous siliciclastic units. 

Pre-Cretaceous regime brines located east of the western margin of the Cooking Lake platform (referred to as central-regime brines in this study) show differing properties and have differing evolutionary histories than those lying to the west of the western platform margin (referred to as western-regime brines). 

Pre-Cretaceous central-regime brines evolved through progressive evapoconcentration to the point of halite saturation as mid-Devonian seawater moved away from the northwestern open-marine connection of the Devonian Elk Point Basin. Brines nearing the southeastern margin of the Elk Point Basin were enriched in K and Li through dissolution of late-stage evaporite minerals (potash) of the Prairie Evaporite Formation. Following infiltration into the underlying Winnipegosis / Keg River Formation, brines were transported westward by gravitationally-driven flow. Regionally-upward groundwater flow, associated with Laramide tectonism, then forced central-regime brines upward into stratigraphically-higher Devonian carbonates, including the Nisku and Leduc formations. 

Pre-Cretaceous western-regime brines evolved through evapoconcentration of mid-Devonian seawater, but not to the point of halite saturation, followed by dissolution of pre-existing halite deposits. K- and Li-enrichment of western-regime brines likely do not represent evaporative processes or interaction with evaporite minerals but, rather, reflect the contribution of hydrothermal fluids. 

The composition of post-Jurassic-regime brines can be largely explained as a mixture of underlying pre-Cretaceous regime brines with varying amounts of meteoric water.