Composite Acid Treatment for Mitigating Formation Damage in Gas Storage Reservoirs

Severe permeability reduction caused by drilling-fluid contamination has significantly impaired injectivity and deliverability in the K gas storage reservoir. This study aims to restore reservoir performance through the optimization and application of a composite acid system. A series of laboratory evaluations combined with core-flow experiments, continuous core scanning, and NMR T2 analysis were conducted to assess acid performance and elucidate damage-removal mechanisms and pore–throat evolution. The results show that the optimized composite acid exhibits favorable compatibility, effective corrosion and precipitation control, a strong clay-stabilization capacity, and high permeability restoration. Core-scale experiments and NMR analyses indicate that the acid selectively removes near-wellbore and deep plugging while restoring pore–throat connectivity without inducing excessive dissolution or framework damage. Field application further confirms the laboratory findings, demonstrating substantial improvements in gas injection and production performance, along with enhanced reservoir energy retention and recovery. Overall, the proposed composite acid system provides an effective and practical solution for mitigating formation damage and improving the long-term injectivity and deliverability of gas storage reservoirs.