Performance of cyclic injections in soft granular media: Trapping efficiency and hysteretic behaviour

Carbon dioxide (CO2) and hydrogen (H2) storage in geological formations are two key approaches to reducing carbon emissions, with capillary trapping serving as one of the primary trapping mechanisms. Understanding the behaviour of immiscible fluid-fluid displacement in porous media is crucial for optimizing trapping efficiency. However, previous studies have primarily focused on single injection scenarios in non-deformable particles, with limited attention given to cyclic scenarios and conditions where the porous media may deform under injection-induced stress. To address this gap, this study experimentally investigates the effects of solid deformability (i.e., hard and soft particles) on trapping behaviours during single and cyclic injections under quasi-2D conditions using a Hele-Shaw cell. In soft media, gas bubbles evolve from cavities to small blobs during cyclic injections, leading to a noticeable increase in residual saturation compared to single injection. In contrast, hard granular media exhibit pore invasion from the onset, with residual saturation remaining independent of the number of injection cycles. These findings demonstrate that solid deformability plays a critical role in governing the dependence of residual trapping on injection schemes. These insights offer valuable guidance for developing more effective and optimized strategies for geological gas storage.