Supercritical Carbon Dioxide Utilization for Hydraulic Fracturing of Shale Reservoir, and Geo-Storage: A Review

Hydraulic fracturing has completely revolutionized how shale resources are exploited to extracthydrocarbons. However, sustainability and environmental issues have fueled the desire for alternate fracturing technologies. Supercritical carbon dioxide (Sc-CO2) fracturing is a new method that uses high-pressure, high-temperature CO2 in its supercritical state (7.38 MPa and 31.1 °C) to generate fractures in shale formations, thereby increasing reservoir permeability. This Review thoroughly analyzes the effects of Sc-CO2 on shale reservoirs during the fracturing process, including the factors that affect fracture breakdown pressure and the complexity and roughness of fracture induced by Sc-CO2. Sc-CO2 can fracture rock at a fracturing pressure lower than that of slick water. CO2, in its supercritical state, shows strong permeability, low viscosity, and extremely low surface tension, like gas, because of which it can infiltrate any space larger than its kinetic diameter (0.330 nm). Many research investigations illustrate how Sc-CO2 affects shales with diverse pore structures, mineral compositions, and mechanical properties when exposed to Sc-CO2 for several hours to days. It is challenging to effectively store CO2 in shale gas reservoirs due to their low permeability and limited storage capacity. To improve the effectiveness of CO2 storage, shale can be fractured to increase the pore space and surface area in reservoirs. Thereby, a certain amount of the CO2 pumped for shale gas production can be securely stored in shale formations, reducing carbon emissions and allowing for a zero-carbon footprint. This paper discusses the pathway and different chemical reactions involved in the storage of CO2 after fracturing over a period. However, fully understanding the interactions between Sc-CO2 and shale rock and the possibility of long-term storage of CO2 in shale formations is quite challenging. It is because of a lack of research and limited knowledge in the above field. Hence, more investigation and development are required in the research area of Sc-CO2 fracturing and the interaction of CO2 with shale rock.