Cyclic CO2 – H2O injection and residual trapping: Implications for CO2 injection efficiency and storage security

•CCS operations at scale will involve periods of changing injection rates.•First experimental study into six cycles of water and scCO2 injection.•Continuous hysteresis generates cumulative residual trapping and pressure increases.•Increased residual trapping increases storage security and efficiency.•Increased residual trapping leads to increased injection pressures.