Quantification of the Effects of the Clean Fracturing Fluid of Mixed Anion-Zwitterionic VES on Methane Sorption Behavior in Bituminous and Anthracite Coals

Fracturing fluid has been a controversial topic attracting significant attention from the public for its applications in oil/gas recovery, but its use can lead to irreversible damage to the environment. Therefore, clean or environmentally friendly fracturing fluid has been sought as a potential solution studied by scientists and engineers from around the world. This paper conducts an investigation to quantify the effects of a clean fracturing fluid made from the anionic and zwitterionic viscoelastic surfactants on coalbed methane production. The medium- and high-rank coals have been chosen and prepared for experimental measurements, including low-temperature N2 sorption, Fourier transform infrared (FTIR) spectroscopy, and methane sorption tests. The results indicate that the fracturing fluid plays a significant role in the methane sorption performance of coal. The improved methane sorption can significantly stimulate the pore connectivity and porosity of coal with physical and chemical processes. The fractal dimension calculated by the N2 sorption data decreases, which means the heterogeneity of the pore structure is reduced. According to the FTIR spectroscopy, the ratios of carboxyl and hydroxyl functional groups have been increased to improve the corresponding wettability of coal after fracturing fluid treatment. The results show that a significant reduction occurs in the methane adsorption capacity of the two coals, 31.32% for Hongyan bituminous coal (HY) and 5.74% for Ulanhada anthracite coal (WL), respectively. Therefore, this work presents the clean fracturing fluid of mixed anion-zwitterionic viscoelastic surfactants to prevent methane adsorption and promote methane release from coal seam, providing a meaningful impact on enhanced coalbed methane production.