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

[Display omitted] •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. Recently, viscoelastic surfactant (VES) fracturing fluids have attracted wide attention because they are highly viscoelastic and environmentally benign. To optimize fracturing fluid formulations for coal reservoir conditions, 135 groups of VES fracturing fluids were prepared. The influence of the cationic surfactant’s hydrocarbon chain lengths on water loss, wettability, viscosity, and temperature resistance were analyzed. To further improve the surfactant’s aggregation capabilities, zwitterionic surfactants were added to fracturing fluids prepared with stearyl trimethyl ammonium chloride (STAC). We found that STAC can reduce water loss more effectively during fracturing than the cationic surfactant hexadecyl trimethyl ammonium chloride (CTAC). Appropriate amounts of cocoamidopropyl betaine (CAB) increased the viscosity and temperature resistance of the fracturing fluid. It is important to note that as the concentration of sodium salicylate (NaSal) increases, the maximum viscosity of VES fracturing fluid with CAB added is twice that of a fracturing fluid without CAB.