Water-rock interaction processes in karst geothermal reservoirs in the Guanzhong basin, China: Perspectives from laboratory experiments

Geothermal resource development is pivotal to global renewable energy strategies, demanding advanced understanding of hydrogeochemical processes. This study focused at the Guanzhong Basin's karst geothermal reservoirs, and water-rock interaction experiments were carried out to examine the mechanisms underlying fluid-reservoir rock interaction during geothermal runoff. Through controlled laboratory experiments, this study demonstrates that at 25 °C, geothermal water-rock interactions cause significant ion depletion (Ca²⁺: 94.48 → 59.40 mg/L; Mg²⁺: 41.36 → 40.96 mg/L; HCO₃⁻: 156.65 → 100.81 mg/L), with ionic ratio coefficients and saturation indices confirming precipitation of dolomite/calcite. Chloro-alkaline indices (CAI<0) validate reverse cation exchange dominance. Temperature modulates reaction intensity by altering mineral solubility (HCO₃⁻ decreases 71 % at 80 °C vs 25 °C to 28.85 mg/L). Initial ionic concentration dictates reaction pathways (precipitation at supersaturation vs dissolution at undersaturation). The type of aqueous solution influences the ion concentration in the initial solution, which in turn influences the hydrogeochemical processes when the water rock interaction continues. This work establishes a temperature-ion abundance co-control model, enabling quantitative geothermal exploitation prediction.