Geochemical Variations in Thermal Fluids After the Construction of Chingshui Geothermal Power Plant, Taiwan

Abstract

The operation of a 3 MWe pilot geothermal power plant during 1981-1993 has resulted in changes in hot fluid chemistry in the Chingshui geothermal field. Long term sampling of discharged waters from production wells were analyzed for chemical and isotopic compositions since 1973. The results show increasing steam ratio and enthalpy, which suggests boiling during the first few years. Moreover, hydrogen and oxygen isotopic ratios of geothermal fluid became lighter. This suggests that meteoric water derived from higher elevation circulated into deeper levels during power plant operation period. Meanwhile, after the power plant shutdown cooler and shallower meteoric water may have seeped into the reservoir to cause slightly lowered temperatures, a decrease in chloride concentrations and heavier hydrogen and oxygen isotopic values. These changes in the characteristics of geothermal fluids suggest that discharging geothermal fluids for power generation had resulted to some geochemical fluctuations in the reservoir of the Chingshui geothermal field.