Fluid flow and geochemistry of the Mississippian aquifers in the Williston Basin, Canada-U.S.A

Water samples collected from 114 producing wells in Mississippian aquifers across the Williston Basin. Results reveal large variations in geochemical and isotopic compositions basin wide. Results show: (i) formation waters have distinct chemical fingerprints; (ii) large variations in isotopic compositions indicate variable flow pathways within the aquifers; (iii) portions of the aquifers host formation waters with a composition similar to original Mississippian seawater. Two separate flow regimes are present in the Mississippian aquifers. One flow regime originates from present-day meteoric water that evolved into a saline brine by halite dissolution and subsequent mixing with a residual brine. The other flow regime originates from a large scale fluid flux occurring at the end of the Cretaceous, that evolved into a saline brine via halite dissolution. These new geochemical data indicate the Mississippian flow system is not a simple regional groundwater flow system, rather highly-variable across the basin.