Enhancement of Storage Efficiency during Carbon Dioxide Sequestration in Depleted Reservoirs

Carbon capture and storage (CCS) is crucial for mitigating atmospheric carbon dioxide (CO₂) levels in the clean energy transition. Depleted hydrocarbon reservoirs, with their proven containment integrity, are promising candidates for CO₂ storage. However, maximizing pore space utilization to enhance storage capacity remains underexplored, particularly in depleted reservoirs where CO₂ transitions from gas to supercritical state during injection and storage. We experimentally investigated the impact of surfactants on CO₂ storage dynamics at the microscale using synchrotron-based high-resolution 3D microcomputed tomography. Experiments were conducted at pressures ranging from 6 to 16 MPa, and a constant temperature of 80 °C, covering both gas and supercritical phases of CO₂. Surfactants significantly reduced CO₂-brine interfacial tension (IFT) and created new flow paths through small pores, increasing CO₂ saturation by 30% at 6 MPa. Although surfactant effectiveness decreased at higher pressures, it still enhanced storage efficiency by 12%, 14%, and 17% at 8, 12, and 16 MPa, respectively. These findings highlight the potential of surfactant-assisted CO₂ storage to optimize injection strategies, thereby contributing to more efficient utilization of depleted reservoirs. By improving storage efficiency, this approach supports global efforts to achieve substantial reductions in CO₂ emissions and combat climate change.