The influence of viscoelastic surfactant fracturing fluids on gas desorption in soft seams

Hydraulic fracturing is an effective method of increasing the permeability of coal seams, which has gradually come into use in underground coal mines. Fracturing fluid is a key factor affecting the improvement. In this study, the way in which viscoelastic surfactant fracturing fluids affect gas desorption in soft seams was analyzed using the zeta potential and scanning electron microscope (SEM)-based methods. The results obtained with the zeta potential method indicated that due to the components of viscoelastic surfactant fracturing fluids, the potential at the coal surface jumped from −16.3 mV to 48 mV, the interaction energy between the fracturing fluid and the coal surface increased, the adsorption potential of the gas decreased and gas desorption increased. The SEM results demonstrated that the number of gas transport channels increased due to the effective dissolution of cement in the acidic viscoelastic surfactant fracturing solution. The cumulative pore volume of the coal samples processed with viscoelastic surfactant fracturing fluids was 0.001 cm3/g, which was 1.8 times the cumulative pore volume of coal samples processed with water. The porosity and connectivity of the coal pores both increased, which was beneficial to gas desorption. Comparative experiments using water and viscoelastic surfactant fracturing fluids were conducted in underground coal mines. The results demonstrated that the amount of gas extracted increased by 26.1% when viscoelastic surfactant fracturing fluids were used. Gas desorption in soft seams was promoted by viscoelastic surfactant fracturing fluids. The new data reported in this study can be used to optimize the use of fluids for underground hydraulic fracturing in Chinese coal mines.