Yajun Song

Underground gas storage (UGS), a critical facility for natural gas peak shaving and supply security, often suffers severe sand production and reservoir property deterioration during high-intensity cyclic injection–production operations, posing risks to both safety and economic efficiency. However, the mechanisms and dynamic evolution of reservoir properties under such cyclic conditions remain poorly understood. In this study, a custom-designed large-scale physical simulation system for weakly cemented sandstone cores was used to conduct systematic experiments under multiple operating conditions. The effects of key parameters—including injection/production flow rate and cycle number—on sand production behavior and permeability evolution were analyzed. Results show that during gas injection, reduced flow velocity drives fine particles deeper into the reservoir, causing deposition, blockage, and significant permeability reduction. Conversely, during production, increased near-wellbore flow velocity induces a partial unblocking effect, leading to partial permeability recovery. Overall permeability variation ranges from 5% to 25%, with diminishing amplitude as cycles progress. Complementary triaxial cyclic loading tests were performed to elucidate rock damage accumulation mechanisms under alternating loads. Damage evolution was quantitatively characterized in terms of Young’s modulus degradation and residual strain accumulation, considering loading stress level, and cycle count. Based on experimental findings and theoretical analysis, an integrated porosity–permeability prediction and rock strength damage model was developed, incorporating both deformation and particle migration processes. A case study on an actual UGS well validated the model, revealing that with increasing injection–production cycles, near-wellbore damage intensifies, the critical sand production pressure drop decreases significantly (by ~26.3% after 10 cycles and ~32.4% after 20 cycles), and the damage zone becomes highly heterogeneous, with azimuthal differences up to 30%. This research clarifies the dynamic response mechanisms of sand production and reservoir property evolution during multi-cycle injection–production in UGS. It establishes a comprehensive workflow from experimental simulation to predictive modeling, offering theoretical and technical guidance for safe operation and optimized sand control in gas storage facilities.