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.