Combined Effects of Temperature, Salinity and Viscosity Changes on Groundwater Flow in the Xinzhou Geothermal Field, South China

The distribution of groundwater temperature and flow can be used to describe the hydrogeological process in a geothermal system, which is of great significance to the exploitation of geothermal resources. The traditional gravity-driven groundwater system theory takes less consideration of thermal convection, resulting in a deviation in the investigation of geothermal systems. The rise of water table and the acceleration of the flow of geothermal water in the discharge section suggest the existence of geothermal buoyancy. The changes in temperature, salinity and viscosity comprise the physical basis for the formation of geothermal buoyancy. Geothermal buoyancy due to free heat convection in a fault-controlled discharge section is discussed in the Xinzhou geothermal field, South China. The geothermal buoyancy is the additional pressure head created by the increase in temperature, increase in salinity and decrease in viscosity. At the convection point, geothermal buoyancy appears and forms a maximum of + 417.6 m. Geothermal buoyancy gradually decreases in the discharge section due to temperature domination. The salinity effect and viscosity effect on geothermal buoyancy are minor and negligible, respectively. Comparing the vertical velocity of geothermal water in the discharge section (32.47 × 10−3 m/d) and the average vertical circulation velocity (3.15 × 10−3 m/d), the geothermal buoyancy has an obvious acceleration effect on groundwater flow in the discharge section. The geothermal buoyancy at typical points provides the framework and control points for geothermal water flow in the discharge section of a geothermal system.