Geochemical interpretation of thermal fluid from the Yangyi high-temperature field, Tibet, China

Abstract

Aquifer temperatures of 12 geothermal wells in the Yangyi field whose measured reservoir temperatures range from 104 to 207°C have been estimated from the chemical composition of the discharged fluid. Subsurface temperatures calculated using silica geothermometers are in agreement within a 10°C range compared to measured temperature, while large differences have been obtained for cation geothermometers due to mixing with cold water, chemical reactions in the upflow, lack of equilibration in the reservoir or because some of the temperature functions used are not applicable. Most of the minerals studied have apparently not equilibrated with the solution in the reservoir. Three types of mixing models have been applied to evaluate the temperature of the hot water component in the geothermal reservoir, the chloride-enthalpy model, the silica-carbonate model and the warm spring silica-enthalpy model. The three models indicate subsurface temperatures of 188-253°C which are similar to those found after drilling.