Wei Zhou

The study of geothermal water hydrochemical characteristics and solute transport evolution can provide a reliable hydrogeochemical basis for the development and protection of geothermal resources. Currently, there is a lack of systematic research on the hydrochemical evolution mechanism of geothermal fields in northern Jinan, which limits the development and use of geothermal fields. In this study, the hydrochemical properties of groundwater in northern Jinan were described by analyzing the hydrochemical characteristics of 16 geothermal water samples and 3 cold water samples. The results show that during the transformation from cold water in the south to geothermal water in the north, the contents of major ions all show an increasing trend and the hydrochemical characteristics show obvious zoning characteristics. The hydrochemical type evolved from HCO₃-Ca to HCO₃-Ca·Mg type, and then further evolved SO₄-Ca and SO₄-Ca·Na type water. Dissolution-precipitation of carbonate, sulfate, halite, and silicate minerals is one of the important processes that controls the chemical characteristics of geothermal water. The water source is mainly from the atmospheric precipitation in the Taiyi Mountain, with an altitude of 698.99-1464.91 m.s.a.l. The thermal reservoir temperature in the study area is estimated to be 55.62-98.16 °C. This paper proposes a conceptual model of the karst geothermal water flow system in northern Jinan, which provides a new idea for exploring the geothermal water genesis mechanism under similar geological conditions.

Porous sandstone geothermal water is an important geothermal resource, which is a low-carbon and clean resource, but lacks systematic research on a regional scale. The northern part of Jinan City is rich in geothermal resources, specifically porous sandstone thermal reservoirs. However, there is still incomplete research on the mechanism of geothermal genesis and the hydrochemical characteristics of geothermal water in porous sandstone. This study aims to address this gap by collecting 21 groundwater samples from northern Jinan and comparing their conventional ion and isotope characteristics to investigate the hydrochemical characteristics during the formation of geothermal water and uncover the genesis mechanism of porous sandstone geothermal water. The results indicate that the geothermal water is classified as Na-Cl type and Na-SO₄-Cl type. The hydrochemical characteristics of geothermal water are primarily influenced by water–rock interaction and groundwater mixing. The water source primarily comes from the atmospheric precipitation in the Taiyi mountains, with an altitude of 910.75–1542.2 m.s.a.l.. The estimated temperature of the thermal reservoir ranges from 51 to 78 °C, and the depth of geothermal water circulation is estimated to be between 1316 and 2216 m. Based on the characteristics of the geothermal field, including the “cap rock, water source, heat source, reservoir, and channel,” a conceptual model of the porous sandstone geothermal water flow system is proposed. This model offers novel insights into the genesis mechanism of geothermal water under similar geological conditions.