Abstract: Estimation of geothermal reservoir temperature plays a key role in the geothermal system research. This study employs geothermometers of geochemistry, mineral equilibria, mixing model with cold meteoric water, and gas to evaluate the reservoir

temperature of different geothermal fields with data archived in the National Geothermal Data System (NGDS), which concludes the
limitations of applications of different methods for determining the reservoir temperature and provides benchmarks for choosing the
appropriate methods to calculate the geothermal reservoir temperature. The results reveal that: 1) The geochemical geothermometer
method is reliable when the geothermal fluids reach the equilibrium between ions and minerals; the SiO2 (silica) geothermometer is more reliable than the cation geothermometer when the geothermal fluids have not reached the equilibrium; 2) The saturation index of the mineral equilibria can provide benchmarks choosing the geothermometers even if it cannot calculate the accurate reservoir temperature due to the selection of limited saturated minerals. For example, the chalcedony geothermometer is better than SiO2 geothermometer to estimate the reservoir temperature of due to the oversaturation of silica based on the multi-mineral equilibrium plot. For the vapordominated high temperature geothermal reservoirs, the minerals and ions cannot reflect the properties of geothermal reservoir, and the gas thermometer will be more successful in predicting the subsurface temperature in high-temperature geothermal systems. The mixing models usually overestimate the reservoir temperature since they pick up the temperature before the hot water gets mixed with the cold water. There is no universal geothermometer since each method has its own assumptions and works for specific geothermal setting. The best approach is to employ various suitable geothermometers and validate the results.

Key words: reservoir temperature, national geothermal data system (NGDS), geochemical geothermometer, multi-minerals equilibrium; mixing model