Viscoelastic surfactant fracturing fluids for use in coal seams: Effects of surfactant composition and formulation

•The micelles formed by STAC can bind more water molecules.•Type and concentration of the surfactant affect wettability of fracturing fluid.•STAC can achieve higher viscosity at lower concentrations in VES fracturing fluid.•VES fracturing fluid formulated with STAC is more suitable for deep coal seams.•The addition of an appropriate amount of CAB aids micelle aggregation.