Geochemistry and Scaling Potential for High Temperature Geothermal Systems Along the Himalayan Belt in China

Abstract

High temperature geothermal resources in China are mainly existed along the Himalayan belt which belongs to one of the global geothermal belts, but it’s not well exploited yet. This paper tries to summarize the geochemical characteristics and possible scaling potential of geothermal fluids in typical high temperature geothermal systems along this belt and provide evidences for further development. Geochemical data of 79 samples from springs and boreholes were collected and analyzed. Results show that strong surface manifestations of hot springs with temperature up to boiling point were observed in Tibet, Western Sichuan and Yunnan area but not in Xinjiang area; reservoir temperature is assessed to be 170-275℃ for most of the geothermal systems along the belt though measured temperature at surface is much lower. Geothermal fluids are Cl-Na, HCO3-Na or Cl•HCO3-Na type dominated and pH ranges from 6.4 to 9.5. Total dissolved solids vary from 170 mg/L to about 4400 mg/L and minor elements like Li, Rb and Cs are in high concentrations. Calculations show that calcite, quartz, chalcedony and amorphous silica are over saturated at wellhead conditions for fluid from these four areas. However, fluid composition reconstruction using WATCH program indicates that at reservoir conditions, calcite from geothermal fluid of Tibet and Taxian of Xinjiang is mainly under saturated while that in Western Sichuan and Yunnan area is over-saturated; quartz, chalcedony and amorphous silica are all under saturated. The oversaturation is caused by CO2 degassing and temperature decrease during upwelling process. Combined with results from adiabatic boiling simulation from reservoir to surface conditions, it’s indicated that calcite scaling will happen in Taxian, Western Sichuan and Yangbajing, Yangyi and Gulu geothermal system in Tibet area while quartz scaling are likely to occur in Yunnan and Dagejia & Langjiu geothermal system in Tibet area.