Effect of supercritical carbon dioxide on pore structure and methane adsorption of shale with different particle sizes

Supercritical carbon dioxide (SCCO₂) fracturing significantly enhances shale gas recovery, which is influenced by particle size. We soaked shale in SCCO₂ and investigated the impact of SCCO₂ on different particle sizes. Large-particle shales showed the largest percentage changes in specific surface area and total pore volume (54.11 %, 87.87 %; 58.59 %, 76.32 %) followed by small-particle size shales. This trend was also observed in other pore structure parameters. The particle-size effect is: Large-particle shale, with abundant microfractures, enhances SCCO₂ flow and pore alteration. Small-particle shale's high specific surface area facilitates SCCO₂ penetration. Medium-particle shale is less affected due to balanced interactions of these factors. Methane is primarily found in large and medium pores and microfractures. Methane adsorption in shale mainly involves multi-layer adsorption. Following SCCO₂ treatment, pore fractures narrowed, increasing the proportion of methane molecules adsorbed as a single-layer. This study is crucial for evaluating the fracturing effects on shale gas wells.