Estimation of reservoir temperature using silica and cationic solutes geothermometers: a case study in the Tengchong geothermal area

Abstract

Reservoir temperature estimation is vitally important for assessing the exploitation potential of a geothermal field. In this study, the concentrations of major chemical constituents in geothermal water sampled from boiling and hot springs in the Tengchong hydrothermal area were measured, and quartz and cationic solutes geothermometers were used to calculate subsurface temperatures. Log (Q/K) diagrams and Na–K–Mg triangular diagrams were applied to evaluating the equilibrium status of geothermal water samples with regard to reservoir minerals, and results were used to select suitable geothermometers. The results show that samples RH01, RH03, RH04, RH05, and LL16 were in or very close to full equilibrium with the selected minerals, and therefore a Na–K geothermometer is appropriate. A K/Mg geothermometer, however, is applicable to LP08 and PZH18 whose chemical compositions adjusted to the shallow reservoir temperatures during their re-equilibrium processes. In contrast, cationic solute geothermometers are unsuitable for SQ20 and RH07, which are categorized as immature water in the Na–K–Mg diagram; a quartz geothermometer was adopted to evaluate the corresponding subsurface temperatures of these samples. According to the reservoir temperature estimation made in this study, there is at least one high-temperature reservoir below Rehai with a possible temperature range of 210–270 °C.