The presence of oxygen impurities in biomethane raises concerns over mineral stability and reservoir integrity during subsurface storage operations. This study evaluates the impact of oxygen on the mineralogical stability of reservoir rocks during subsurface biomethane storage using laboratory batch experiments, complemented by batch reactive modelling to interpret short-term behaviour and explore longer-term re-equilibration trends. Two geologically distinct reservoir samples, representing sandstone and marlstone formations, were subjected to controlled oxygen-brine-rock interactions under reservoir-relevant conditions. Geochemical analyses show minor alterations in fluid composition and minimal mineralogical changes that primarily involve slight variations in clay and carbonate mineral phases. Batch modelling further supports these findings, demonstrating limited mineral dissolution and precipitation reactions over both short- and long-term scenarios. A key aspect of this study is the direct comparison between oxygen- and nitrogen-exposed systems under matched conditions, which allows oxygen-specific geochemical effects to be isolated from generic gas-brine-rock interactions. Overall, the results indicate that oxygen impurities at typical biomethane concentrations are unlikely to cause significant formation damage, providing valuable insights for setting oxygen tolerance limits in subsurface biomethane storage operations. This study contributes to the broader understanding of subsurface geochemical processes relevant to energy storage. Further studies are nevertheless required, involving longer-term experiments and reactive transport modelling, while taking microbial activity into account. • Experiments and modelling used to evaluate geochemical effects of oxygen impurities during subsurface biomethane storage. • Site-specific lithology influences geochemical behaviour under oxygen exposure. • Direct comparison of oxygen- and nitrogen-exposed systems reveals oxygen-specific responses. • Batch modelling indicates long-term stability with minimal mineral dissolution or precipitation. • Quartz- and carbonate-dominated rocks show negligible geochemical alteration due to oxygen. • Findings support the safe storage of biomethane with low-level oxygen impurities in porous formations
Jangda et al. (Sun,) studied this question.