Microbubble CO₂ Injection in High- Perm Sandstone: Flow-Rate Effects and Permeability Decay

Abstract Microbubble (MB) CO₂ injection has been proposed to improve sweep efficiency and dissolution trapping, yet its implications for injectivity and near-wellbore integrity in high-permeability formations are not well constrained. We conducted repeated volume-balance core-flooding experiments on high-permeability Berea sandstone (~ 980 mD) under deep saline aquifer conditions (40°C, 10.7 MPa), comparing MB and conventional supercritical CO₂ injections across flow rates of 0.05–0.5 cc/min (Ca : 1.15–11.5 × 10⁻⁹) while monitoring brine permeability. At 0.05 cc/min, MB injection increased average CO₂ saturation by 8.9% relative to conventional flooding due to temporary microbubble-induced blockage of dominant flow channels. This benefit diminished at higher flow rates (0.1–0.5 cc/min), where MB injection consistently yielded lower final CO₂ saturations. Across sequential floods, MB injection caused brine permeability to decline up to four times faster than conventional injection, indicating accelerated near-wellbore damage likely driven by fines mobilisation and enhanced mineral reactions associated with rapid microbubble dissolution. These results demonstrate a clear trade-off in MB CO₂ injection: potential sweep-efficiency gains at low flow rates versus permeability loss and injectivity difficulties at higher flow rates. The results of this study suggest the need for further research under higher flow rates considering practical operation and optimising microbubble-based storage strategies will require careful control of flow rate and consideration of reservoir heterogeneity in high-permeability systems.