Analysis of the competitive influence of gas adsorption and interface modification on the surface free energy of coal matrix

Abstract

Coal is a complex porous medium characterized by numerous pores and fractures within its internal structure, which provide a natural space for the storage of coalbed methane. The high surface free energy of coal significantly inhibits the efficient extraction of coalbed methane, resulting in the escape of considerable amounts of greenhouse gas during the later stages of coal mining. This exacerbates the challenges and costs associated with environmental governance. According to the principle of minimum capacity, the surface of the coal matrix reduces its surface free energy through gas adsorption. To investigate the competitive influence of gas adsorption and interface modification on the surface free energy of the coal matrix, isothermal adsorption and contact angle determination experiments were conducted. The results indicate that as equilibrium pressure increases, the amount of gas adsorption on the surface of the coal matrix also increases, while the adsorption potential exhibits a contrasting trend. Under the influence of gas adsorption, there is a significant increase in Gibbs variation, indicating a substantial decrease in the surface free energy of the coal matrix. Under the influence of interface modification, an increase in surfactant concentration resulted in a trend of energy reduction characterized by an initial increase followed by a subsequent decrease. Moreover, interface modification effectively eliminated the water-blocking effect, leading to a significant enhancement in gas desorption. Consequently, interface modification offers important theoretical support for improving production in coalbed methane and mitigating the greenhouse effect.