Delineation of a Brine Interface in the Salton Sea Geothermal System, California

Abstract

Fluids in the Salton Sea Geothermal System (SSGS) cluster into two distinct populations in terms of their salinity. The hot, hypersaline brine for which the SSGS is known, is overlain by a cooler (<260°C) fluid with distinctly lower salinity. Both types of fluid are produced from closely spaced production intervals in geothermal wells, indicating that a sharp salinity interface exists over much of the fluid. Sedimentary features are typically cross cut by the fluid interface, which parallels the elongate dome like thermal structure of the SSGS. The fluid interface occurs in portions of the reservoir where temperatures are 260°C. Hypersaline brines have densities of approximately 1.0 gm/cm3 while the low TDS fluids have densities as low as .85 gm/cm3. The stable, density stratified interface implied by the data should act as a barrier to convective heat and mass transfer in the SSGS, isolating the hypersaline reservoir form overlying dilute fluids.