Influence of a Nanoparticle-Enhanced Gemini VES Fracturing Fluid on Methane Adsorption Characteristics of Coal

To elucidate the effect of a nanoparticle-synergistic Gemini VES (NPs-Gemini VES) fracturing fluid on methane adsorption in coal, coal samples were immersed in the SiO2 nanoparticle-enhanced Gemini VES fracturing fluid for different time durations. The changes in the methane adsorption behavior were evaluated using a magnetic suspension balance. On the basis of the experimental results, a coal–NPs-Gemini VES model was constructed in Materials Studio (MS), and grand canonical Monte Carlo (GCMC) simulations were performed to investigate methane adsorption capacity, adsorption configurations, and intermolecular interaction energies. The molecular interactions among coal, fracturing fluid components, and methane were analyzed to clarify their competitive adsorption behavior on the coal surface. The results indicate that all fracturing fluid systems suppressed methane adsorption, with the greatest reduction observed for the NPs-Gemini VES treatment. At 0.5 MPa, methane adsorption decreased by 20.87% and 34.15% after 24 and 96 h of treatment, respectively, whereas the reductions in the other systems plateaued after 24 h. At 2 MPa, the electrostatic interaction energies of the coal–Gemini VES and coal–NPs-Gemini VES systems were 31.96% and 49.22% higher, respectively, than those of the coal–water system, enabling the Gemini VES-SiO2 composite structure to preferentially occupy high-energy adsorption sites. Furthermore, the interconnected composite network formed by the NPs-Gemini VES fracturing fluid occupied the effective adsorption space available for methane and enhanced interfacial water occupancy by modifying the interfacial properties, resulting in methane adsorption at the remaining low-energy adsorption sites with reduced adsorption stability. These effects substantially weakened the methane adsorption capacity of the coal.