Hydrogeochemical Modeling of the Shallow Thermal Water Evolution in Yangbajing Geothermal Field, Tibet

The exploitation of thermal water and the mix of cold water changed the properties of geofluid in shallow reservoir, which altered the concentration of the chemical constitutes and continuously built new water-rock reaction. This paper deduced reservoir pressure and temperature variation tendency from 2004 to 2013, analyzed the change of some components in the shallow reservoir water, and finally obtained the evolution of the shallow geothermal water with hydrogeochemical model. The results show the reservoir pressure decreased significantly compared with the slight decline of reservoir temperature, and much cold groundwater infiltrated into the shallow reservoir, which affected the solubility of SiO2 and led to precipitation, the increased CO2 in shallow reservoir promoted the dissolution of aluminosilicate. Calcite and kaolinite precipitation zone has extended to the north in the field, which influenced the porosity of the reservoir rock.