Carbon dioxide storage within coal reservoirs: A comprehensive review

Storing carbon dioxide (CO2) resulting from the burning of fossil fuels in geological formations could be an environmentally appealing approach to mitigate the volume of greenhouse gas emissions. Among the geological choices available, storing CO2 in coal deposits offers numerous benefits. For instance, injecting CO2 can boost methane production from coal reserves, coal has the capacity to securely retain CO2 for extended durations, and there are promising coal basins near various CO2-emitting sources that contain suitable formations for sequestration. Practical trials involving the storage of CO2 in coal seam reservoirs have encountered significant challenges, primarily the decline in injectivity resulting from coal swelling and extensive loss due to the concentration of the reservoir's cleat system. CO2 sequestration in coal reservoirs carries several potential risks, including leakage CO2 if not properly contained, which can migrate through the geological formations. Additionally, it can induce seismicity—the injection of CO2 may increase pore pressure in the coal reservoir, potentially triggering seismic activity, especially if the pressure buildup leads to fault. There are also concerns about reservoir integrity, as the injection of CO2 can alter the structural and mechanical properties of the coal reservoir, leading to coal swelling, and environmental impacts. In this research, our objective is to review and reassess research related to the storage of CO2 in coal reservoirs. This study concentrates on the alterations in characteristics and responses of coal formations resulting from CO2 exposure in the context of CO2 sequestration. We emphasize the key discoveries from existing research up to this point and suggest areas with significant potential.