Advances and Prospects of Supercritical CO₂ for Shale Gas Extraction and Geological Sequestration in Gas Shale Reservoirs

The advancements in hydraulic fracturing and horizontal drilling techniques have substantially facilitated the large-scale extraction of natural gas from shale gas reservoirs. However, the use of fracking water poses several potential drawbacks including the contamination of groundwater, surface water, and soil, as well as risks to air quality. Due to the unique physical properties of supercritical CO2, shale gas exploitation using this method has been considered a promising technology that can not only improve gas recovery but can also enable CO2 geological storage. This paper clarifies the gas adsorption mechanism in shale formations, including the factors influencing the adsorption of CH4, the differences between CH4 and CO2 adsorption, and various adsorption models. We show that shale inherently exhibits a preference for CO2 adsorption over CH4. Then, the supercritical CO2 fracturing mechanism, including the shale fracking pressure and the factors influencing CO2 fracturing, is analyzed. The mechanisms of CO2 extraction in shale gas and the key factors influencing CO2 geological storage are discussed. The main challenges and future prospects regarding the use of supercritical CO2 for shale gas recovery and geological sequestration in gas shale reservoirs are finally summarized. A more detailed understanding is required to evaluate the efficiency of shale gas recovery and CO2 geological sequestration in shale formations using supercritical CO2. This work provides a basis and serves as a reference for future research investigating the mechanisms of shale gas exploitation using supercritical CO2, as well as the limitations and advantages of CO2 geological sequestration in unconventional shale gas reservoirs.