Hysteresis and integrity in multiphase hydrogen storage: a review of flow, rock, and monitoring challenges

Underground hydrogen storage (UHS) is increasingly recognized as a cornerstone technology for large-scale energy transition, yet its implementation remains hindered by limited understanding of hysteresis and coupled multiphysics interactions that control storage efficiency and containment security. Experimental, modeling, and field evidence are synthesized to elucidate the mechanisms governing hydrogen (H2) trapping, wettability alteration, chemo-biomechanical feedbacks, and integrity evolution across scales, integrated within a framework of three interconnected pillars: hysteresis, integrity, and monitoring. Key research gaps are identified, including the scarcity of H2-specific experiments under reservoir-relevant conditions, limited understanding of upscaling and heterogeneity representation, inadequacy of current simulation tools for dynamic and coupled processes, and insufficient integration of monitoring technologies. Based on these findings, a structured research roadmap is proposed, encompassing multiscale hysteresis characterization, chemo-bio-mechanical coupling, machine-learning-enhanced, THMC modeling, and multi-sensor data fusion. This assessment provides a unified framework for bridging laboratory observations and field-scale uncertainties, thereby supporting the development of predictive, secure, and economically viable UHS systems.