CO₂ injection in shale reservoirs is more suitable than the conventional recovering methods due to its easier injectivity and higher sweep efficiency. In this work, Grand Canonical Monte Carlo (GCMC) simulation is employed to investigate the adsorption/desorption behavior of CH₄-C₄H₁₀ and CH₄-C₄H₁₀-CO₂ mixtures in organic and inorganic nanopores during pressure drawdown and CO₂ huff and puff processes. The huff and puff process involves injecting CO₂ into the micro- and mesopores, where the system pressure is increased during the huffing process and decreased during the puffing process. The fundamental mechanism of shale gas recovery using the CO₂ injection method is thereby revealed from the nanopore-scale perspective. During primary gas production, CH₄ is more likely to be produced as the reservoir pressure drops. On the contrary, C₄H₁₀ tends to be trapped in these organic nanopores and is hard to extract, especially from micropores and inorganic pores. During the CO₂ huffing period, the adsorbed CH₄ and C₄H₁₀ are recovered efficiently from the inorganic mesopores. On the contrary, the adsorbed C₄H₁₀ is slightly extracted from the inorganic micropores during the CO₂ puffing period. During the CO₂ puff process, the adsorbed CH₄ desorbs from the pore surface and is thus heavily recovered, while the adsorbed C₄H₁₀ cannot be readily produced. During CO₂ huff and puff, the recovery efficiency of CH₄ is higher in the organic pores than that in the inorganic pores. More importantly, the recovery efficiency of C₄H₁₀ reaches the highest levels in both the inorganic and organic pores during the CO₂ huff and puff process, suggesting that the CO₂ huff and puff method is more advanced for heavier hydrocarbon recovery compared to the pressure drawdown method. In addition to CO₂ storage, CO₂ sequestration in the adsorbed state is safer than that in the free state. In our work, it was found that the high content of organic matter, high pressure, and small pores are beneficial factors for CO₂ sequestration transforming into adsorbed state storage.

Prolonged high-concentration CO₂ mineralization may enhance early-age strength but cause a late-age strength decline in cementitious backfill materials. This study investigated how ground glass fiber (GGF) dosage (0%, 1%, and 2%) affects fly ash–cement backfill materials under conventional hydration and prolonged CO₂ mineralization curing. Compressive strength was measured at 3, 7, and 28 d, together with X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, mercury intrusion porosimetry, and scanning electron microscopy with energy-dispersive spectroscopy. Under CO₂ mineralization, the 0% GGF mixture decreased from 22.42 MPa at 7 d to 14.32 MPa at 28 d, indicating a 36.1% strength decline. Increasing GGF dosage to 1% increased the 28 d strength to 21.07 MPa and reduced the 7–28 d strength decline to 22.2%, whereas 2% GGF provided no further improvement. GGF also increased strength under conventional hydration, indicating a general strengthening effect together with improved late-age strength retention under CO₂ curing. TGA showed increased carbonate-related mass loss after mineralization, but 1% GGF did not further increase it, while MIP showed lower total porosity but larger median pore size. These results indicate that the strength benefit of 1% GGF was not governed by greater carbonate formation or overall pore refinement and may involve local particle–matrix interactions.