Study on Porosity and Permeability Characteristics of Sandstone Geothermal Reservoir Under Recharge Conditions: A Case Study of Decheng District, Shandong Province

Against the backdrop of growing concerns over environmental degradation and fossil fuel harms, geothermal energy—clean, low-carbon, widely distributed, and stably supplied—has gained increasing attention, becoming a key focus of renewable energy research. This study focused on a typical doublet-well system in Decheng District, Shandong Province, China, a region with mature geothermal development and high recharge demand. To investigate the water–rock interaction mechanism and its impact on reservoir properties, we combined indoor high-temperature/pressure static experiments with a hydro–thermo–chemistry coupling numerical simulation using TOUGHREACT V4.13-OMP. Experimental validation was conducted by matching the simulated major ion concentrations and pH values with the experimental results, confirming the reliability of the model parameters. The methodology integrated mineral composition analysis (XRD/XRF), hydrochemical testing of reaction solutions, and long-term numerical simulation of the doublet-well system under 50 heating cycles. The key qualitative results include the following: (1) feldspar minerals (sodium/potassium feldspar) are the main dissolved minerals, while dolomite and illite are the dominant precipitated minerals during recharge; (2) recharge-induced mineral precipitation causes significant near-well pore plugging, leading to continuous attenuation of porosity and permeability; (3) reducing Ca2+/Mg2+ concentrations in recharge water effectively alleviates permeability reduction, providing a feasible optimization direction for geothermal recharge schemes worldwide. This study enriches our understanding of sandstone geothermal reservoir evolution under recharge conditions and offers practical references for optimizing recharge strategies in similar geothermal fields globally.