Mitigating Injectivity Loss During Phase-Coupled CO2 Injection into Depleted Gas Reservoirs: Mechanisms, Modeling, and Operational Guidelines

Abstract Depleted gas reservoirs (DGRs) are increasingly recognized as promising geologic formations for large-scale CO2 storage due to their existing well infrastructure, known geology, well-characterized storage formation, geologically-tested natural gas containing reservoir, and substantial pore volume. However, subcritical CO2 injection into DGRs can trigger complex near-wellbore phase-coupled phenomena (such as Joule–Thomson cooling, hydrate formation, salt precipitation, and fines migration) that can significantly impair injectivity. This study synthesizes peer-reviewed literature and laboratory studies to (1) identify the dominant mechanisms of injectivity loss in DGRs, (2) examine modeling approaches used to study these phenomena, and (3) translate findings into operational guidelines for mitigating risk. Quantitative synthesis indicates that combined physical-chemical mechanisms can reduce near-wellbore permeability by up to approximately 70%, with fines migration and salt/hydrate precipitation being particularly critical. Operational strategies supported in the literature include preheating CO2, gradual injection ramp-up, moderate water saturation, and high-resolution thermal/pressure monitoring. Key research gaps remain in field-scale demonstration, integrated laboratory studies under reservoir conditions, pore-scale kinetics of hydrate/salt formation, and techno-economic evaluation of mitigation measures. This study provides a structured framework to guide design, monitoring, and operation of CO2 injection into DGRs, supporting safe and efficient carbon storage deployment.