Heqing Lei

Geothermal reinjection is critical for sustainable exploitation of geothermal resources, yet the permeability evolution mechanism of carbonate geothermal reservoirs remains poorly understood. Taking dolomite geothermal reservoirs of the Wumishan Formation in the Xiong’an New Area as the research object, high-temperature and high-pressure dynamic flow experiments and TOUGHREACT simulations were performed to investigate the effects of injection pressure, temperature, and water chemistry on the permeability of matrix and fractured cores. Results show that the optimal injection pressure and temperature for both core types are 14 MPa and 70 °C. Under such conditions, the final average permeability of matrix and fractured cores is 0.0015 mD and 0.0287 mD, with CV values of 7.3% and 6.2%, respectively. Chemically treated water suppresses calcite dissolution by altering ionic composition and pH, thereby reducing permeability of both cores, while the reduction is less significant for fractured cores. Simulations indicate that reinjection water triggers slightly stronger calcite dissolution than dolomite precipitation and yields permeability enhancement. When treated water is injected, reaction intensity declines, Mg²⁺ concentration approaches zero, and dolomite precipitation becomes more thorough. Matrix cores follow an “activation-stabilization” pattern, whereas fractured cores exhibit a “decay-convergence” pattern and are more sensitive to pressure. This study reveals distinct responses of matrix and fractures to hydrochemical perturbations in dual-porosity carbonate geothermal reservoirs, demonstrating that permeability evolution during reinjection is jointly governed by reservoir pore type and hydrochemical conditions. The findings provide mechanistic support for targeted regulation of reinjection water chemistry.

Driven by China’s “Dual Carbon” strategy, medium-deep closed-loop geothermal energy has become a mainstream clean heating technology owing to the advantage of “heat extraction without groundwater production”. However, its large-scale application is restricted by low single-well heat output and an unclear matching mechanism between working fluids and wellbores. Taking sandstone geothermal reservoirs in Dezhou, Northwestern Shandong Depression, as the research object, a 3D coupled heat transfer model of the wellbore–reservoir was established via COMSOL Multiphysics. The heat transfer characteristics of water and CO₂ under variable injection temperature, mass flow rate and wellbore layout were compared. The results show that: (1) injection temperature dominates the heat extraction performance of water, which matches branched wells and delays overall reservoir thermal depletion during long-term exploitation; (2) CO₂ performance is highly sensitive to mass flow rate and suitable for connected wells, and an asymmetric geothermal field with “cooled injection zone and heated production zone” forms under a high flow rate; (3) limited by low specific heat capacity, CO₂ delivers lower heat power at an identical flow rate, while equivalent heat yield can be achieved when its flow rate doubles that of water. This study clarifies matched development schemes for two working fluids and provides a theoretical reference for optimized exploitation of closed-loop geothermal systems in sandstone reservoirs in Northwestern Shandong.

Reinjection represents a fundamental strategy for sustainable geothermal reservoir development. During reinjection, reservoirs are subjected to pronounced physicochemical disequilibrium, under which complex water–rock interactions render long–term behavior difficult to predict. This review synthesizes mineral reactions and reservoir dynamic responses from a geochemical perspective. The interplay between reaction kinetics and fluid transport is examined using the Damköhler number, elucidating the spatiotemporal evolution of reactive transport. The dissolution–precipitation behaviors of silicate, carbonate, and sulfate minerals are evaluated, highlighting their distinct roles in governing long–term structural reorganization, short–term permeability variability, and rapid clogging. The influence of mineral reactions on pore structure evolution and the development of nonlinear porosity–permeability relationships is examined, alongside commonly used constitutive models and their inherent limitations. Multiscale characterization approaches for porosity–permeability evolution and the distinct responses of different reservoir types are reviewed. The chemo–mechanical coupling induced by water–rock interactions and its implications for reservoir stability are addressed. This work establishes a unified conceptual framework linking mineral reactions, fluid transport, and reservoir evolution, providing a basis for optimizing reinjection strategies and improving long–term geothermal system performance.