Viscoelastic surfactant fracturing fluid for underground hydraulic fracturing in soft coal seams

Hydraulic fracturing is an effective and increasingly popular method of improving the permeability of coal deposits. However, fracturing fluids specifically designed for coal deposits are required, as the properties of the fracturing fluid can affect the permeability improvement. A numerical model and rheological tests were used to determine the optimum viscosity and composition of fracturing fluid for underground fracturing. The effect of this optimized viscoelastic surfactant fracturing fluid on coal porosity, gas adsorption and permeability were experimentally investigated and compared with water as a fracturing fluid. Results showed that the viscoelastic surfactant fracturing fluid increased coal pore volume and surface area by 33.9% and 30.6% respectively, compared with samples processed with water. Adsorption and permeability tests on the coal samples processed with viscoelastic surfactant fracturing fluid and water showed that the adsorption capacity was reduced by 22.4% when using viscoelastic fracturing fluid, while the permeability increased by 178%. Using viscoelastic surfactant fracturing fluid can increase the fracturing area and promote gas desorption and seepage, thus improving gas extraction. The results of this study demonstrate the potential for applying of viscoelastic surfactant fracturing fluid in underground fracturing in coal mines.