Deciphering the Synergistic Regulatory Mechanism of Acetic Acid and [Bmim][BF₄] on the Competitive Adsorption of CH₄/CO₂ and Coalbed Methane Recovery Efficiency

With the development in coalbed methane (CBM) extraction technology, fracturing fluid technology has become a critical method for enhancing recovery efficiency. The effects of various fracturing fluids (H₂O, acetic acid (HAc), [Bmim][BF₄], and HAc + [Bmim][BF₄]) on CBM recovery efficiency were investigated through MD simulations. Distinct regulatory effects on gas adsorption and desorption were observed for different fracturing fluids. In the Wiser + H₂O system, H₂O molecules formed compact clusters, occupying adsorption sites and promoting methane desorption. Interestingly, the addition of HAc resulted in looser fracturing fluid clusters in the Wiser + HAc system, enhancing coal surface coverage, desorption efficiency, and fluid flowability. Following the addition of [Bmim][BF₄], the synergistic effect of HAc and [Bmim][BF₄] led to even looser clusters, achieving the highest desorption efficiency. Moreover, the synergistic system demonstrated the highest displacement efficiency at moderate and low pressures. Quantum chemistry calculations further elucidated the interaction mechanisms between fracturing fluids and coal molecules, revealing that [Bmim][BF₄] molecules enhanced the regulatory effect of fracturing fluids. Specifically, the contact area between clusters and coal surfaces was increased, promoting gas desorption, and the interaction between fluids and coal molecules was weakened, facilitating fluid backflow. The results provide a theoretical foundation for optimizing CBM recovery.