Abstract
The karst geothermal reservoir, Sinian Dengying Formation was investigated from the hydrogeochemical perspective. Integrated techniques including XRD + SEM, isotopes, saturation index and PHREEQC modeling were applied. With 37.3–72 ?, the targeted waters indicate low-mediate temperature geothermal reservoir. The CO2 concentration in the geothermal waters varies from 1.2 mg/L to 52.42 mg/L, and the log(PCO2) value ranges from −2.53 to −1.29, indicating an open carbonate system. A further D-18O stable isotope analysis addresses the geothermal waters are replenished by meteoric water from +815.52 m to +1427.78 m. Strong water-rock interactions are indicated by apparent 18O shift. The dominating hydrochemical type is SO4·HCO3-Ca·Mg with some Cl-Na. The CO2-TDS-SI-Carbonates comprehensive analysis illustrate the origin of Ca2+, Mg2+, and HCO3−, mainly from dolomite. The correlation of 18O-SO42-SI_Gypsum gives sound evidence for the processes of gypsum dissolution. Three inverse models were established and the results showed, that geothermal waters are controlled by two major factors: 1) the adjacent location to salt basin geological profiles with halite dissolution; and 2) the clay minerals such as Na-montmorillonite causing cation exchanges between Na+ and Ca2+ in the geothermal waters, resulting in excess of Na in relation to Cl concentrations.