Geochemical and lithium isotope characterization of Ogallala aquifer and Permian Basin carbonate reservoir waters at an enhanced oil recovery site, northwest Texas, USA
Geochemical and lithium isotope compositions (δ7Li) of Permian Basin produced waters and groundwater from overlying aquifers at an enhanced oil recovery (EOR) site in Gaines County, northwest Texas were determined to evaluate the effects of brine-groundwater-rock interactions, identify sources of dissolved solids, and characterize fluid migration and mixing processes. δ7Li values for produced waters from dolostones of the Permian Basin San Andres Formation ranged from +11 to +16 per mil (‰) and fall within the range of formation waters from Gulf of Mexico and Appalachian basin oil and gas reservoir rocks. The chemical composition and TDS content (800 to 2,200 mg L-1) of water from five Tertiary Ogallala Formation groundwater wells in the study area is comparable to other groundwaters from the Southern High Plains aquifer. Groundwaters from the Triassic Dockum Group Santa Rosa (δ7Li range of +21 to +23) are isotopically distinct from waters from the San Andres and Ogallala Formations. In addition to tracking groundwater-brine mixing and water-rock interaction, temporal changes in the δ7Li composition of deep groundwater in the study area has potential use in the early detection of upward or injection-induced brine migration, prior to its incursion into the sensitive overlying Ogallala aquifer
