Effects of solid deformability and cyclic injections on fluid trapping behavior in porous media

: Geological storage of carbon dioxide (CO 2 ) and hydrogen (H 2 ) is a promising strategy for reducing carbon emissions, underscoring the need to optimize the storage performance. While most prior research has focused on single injections in non-deformable media, less attention has been given to cyclic injection regimes and porous systems that deform under injection-induced pressures. This study experimentally investigates the effects of particle deformability ( i.e. , soft and hard materials) and injection schemes ( i.e ., single and cyclic injections) on gas trapping behaviours using a quasi-2D Hele-Shaw cell. In soft media, cyclic injections notably enhance gas retention compared to single injection, with trapped gas evolving from large cavities to interconnected ganglia and ultimately to discrete blobs. These trapped clusters reduce local porosity and promote further trapping in subsequent cycles. In contrast, the hard case, where traditional capillary trapping dominates, shows residual saturation remaining independent of injection cycling. Comparisons with the Land model and prior studies indicate that hard granular media follow the predicted hysteresis trajectory, consistent with experiments under ambient pressure. By contrast, soft media exhibit enhanced trapping efficiency, resembling behaviour observed under MPa-level pore pressures, suggesting that elevated pressures may induce pore-scale deformation even in nominally rigid rocks. Importantly, a strong correlation between pressure trends and residual saturation suggests that pressure monitoring may serve as a proxy for estimating gas entrapment. These insights provide guidance for optimizing geological gas storage strategies, particularly for improving the efficiency and reliability of H 2 withdrawal and long-term CO 2 sequestration security.