Numerical simulation of hydrochemical evolution of deep pore thermal reservoirs in shallow groundwater recharge of Yancheng uplift

This article relies on PHREEQC software, the hydrochemical model of the main development thermal reservoir of shallow groundwater recharge is constructed by using the dissolution kinetic rate formula. The 120-day recharge period is used to simulate the change of the hydrochemical composition of the thermal reservoir within one year.Simulation results indicate that allochthonous recharge sources have modified the hydrochemical characteristics of the geothermal reservoir within a specific range. During the recharge process, the hydrochemical field is mainly controlled by water runoff and dispersion. Taking the recharge well as the center, the hydrochemical type on the radial direction gradually changes from Na-HCO₃•SO₄•Cl to Na-HCO₃•Cl•SO₄, Na-Cl•HCO₃•SO₄, Na-Cl•SO₄•HCO₃, Na-Cl•SO₄, Na-Cl•SO₄•HCO₃, Na-Cl•SO₄ gradually changes into Na-Cl type, showing a trend of gradual transition from recharge to geothermal water in hot reservoirs.After the recharge stopped, the hydrochemical type near the recharge well changed from runoff and dispersion control to water-rock reaction and dispersion control.Continuous reinjection for 120 days induced a 0.35% reduction in reservoir porosity and permeability attenuation‌. Structural deterioration intensified after reinjection cessation, with porosity decline reaching 3.35% by 180 days, indicating irreversible pore structure degradation in the thermal reservoir.