Enhancing residual trapping of supercritical CO₂ via cyclic injections

We utilize synchrotron X-ray tomographic imaging to investigate the pore-scale characteristics and residual trapping of supercritical CO₂ (scCO₂) over the course of multiple drainage-imbibition (D-I) cycles in Bentheimer sandstone cores. Capillary pressure measurements are paired with X-ray image-derived saturation and connectivity metrics which describe the extent of drainage and subsequent residual (end of imbibition) scCO₂ trapping. For the first D-I cycle, residual scCO₂ trapping is suppressed due to high imbibition capillary number (Ca ≈ 10⁻⁶); however, residual scCO₂ trapping dramatically increases for subsequent D-I cycles carried out at the same Ca value. This behavior is not predicted by conventional multiphase trapping theory. The magnitude of scCO₂ trapping increase is hysteretic and depends on the relative extent of the sequential drainage processes. The hysteretic pore-scale behavior of the scCO₂-brine-sandstone system observed in this study suggests that cyclic multiphase flow could potentially be used to increase scCO₂ trapping for sequestration applications.