Geochemical and lithium isotope tracking of dissolved solid sources in Permian Basin carbonate reservoir and overlying aquifer waters at an enhanced oil recovery site, northwest Texas, USA

摘要

Geochemistry and lithium isotope compositions (delta Li-7) of Permian Basin produced water and potable ground-water from overlying aquifers at an enhanced oil recovery (EOR) site in Gaines County, northwest Texas, are used to evaluate the effects of brine-groundwater-rock interactions, identify sources of dissolved solids, and characterize fluid flow and mixing processes. delta Li-7 values (per mil deviations from the LSVEC standard Li-7/Li-6 ratio) for produced water from dolostones of the San Andres Formation ranged from + 10.9 to + 15.6 parts per thousand and fall within the range of formation waters from other sandstone/carbonate reservoir rocks in North America, Europe and the Middle East. These differ from produced waters from hydraulically fractured shales from the U.S. Appalachian Basin, including the Marcellus Shale, which tend to have lower delta Li-7 values and higher Li/Cl, possibly indicating greater interaction with a terrigenous component. The San Andres produced water chemistry and Li isotope ratios are consistent with Neogene meteoric water interacting with marine and continentally-derived evaporites (e.g., portions of the Guadalupian Salado Formation), as well as other terrestrial sources along the flow path.