Estimation of reservoir temperatures of geothermal systems using solute geothermometers - considerations and limitations

Applicability and limitations in utilizing the solute geothermometers to estimate the reservoir temperatures of geothermal system are evaluated in this article. For this purpose, Los Azufres geothermal field (LAGF), Mexico is taken up as a case study by estimating the reservoir temperatures using all the available solute geothermometers for fluids of thermal springs and geothermal wells. Water samples of the thermal springs around the LAGF are immature type, without any equilibrium with the host rocks, and indicated inconsistent reservoir temperatures. Whereas the fluids of the geothermal wells of LA GF are mature type showing complete equilibrium with the host rock with temperature of equilibrium for fluids of majority of the wells between 300 and 330°C and indicated the reservoir temperatures more comparable to BHT. The temperatures of equilibrium conditions are higher than the BHT for fluids of majority of geothermal wells. Among all the solute geothermometers, Na K geothermometers for fluids of geothermal wells have indicated comparably consistent reservoir temperatures, although somewhat overestimated in comparison to their respective bottom hole temperatures. It is recommended not to apply solute geothermometers routinely without considering the basic requirements and suggested some considerations for their better applications.