Geochemical Characteristics of Waters from Reservoir of the Hydrothermal System of Las Tres VÌrgenes, B.C.S. MÈxico

Abstract

The liquid dominated Las Tres VÌrgenes geothermal reservoir produces brines of Na-Cl type. The reservoir temperature is 280?C and the fluid is in equilibrium with reservoir rocks. There is a good agreement in the estimated temperature from the composition of gaseous and aqueous species. The chemical composition of gaseous species is similar to most of the geothermal reservoirs in Mexico. In wells Lv-1 and Lv-3, the gas content is less than 1% by weight. The CO2 is >95% by weight of the total dissolved gases. Thus, at 280?C, the reservoir gases are also in equilibrium with the liquid phase. The isotopic composition of the wells presents enrichment in 18O, typical characteristic of geothermal origin fluids. The springs in the region present different isotopic and geochemical characteristics. For example, El Azufre (M1) and Agua Agria (M3) have acid-sulfate character, which is related to geothermal zones where the vapor absorption and H2S oxidation are the dominating processes. The isotopic composition of these springs has been changed by evaporation. The other springs do not show any signature of geochemical influence. The isotopic compositions of these springs are closed on the meteoric water line. Their water is saline and contains exchangeable sodium resulting in the waters that are not suitable for even agricultural usages.