Experimental study of the fracturing-wetting effect of VES fracturing fluid for the coal seam water injection

Abstract

To improve the efficiency of coal seam water injection, a viscoelastic surfactant (VES) fracturing fluid that is widely used for the coal-bed methane mining was studied for the coal mine water injection. The composition and gel breaking strategy of the VES fracturing fluid with cationic viscoelastic surfactant as the major component were optimized and evaluated upon viscosity, shear stability, cleanness of gel breaking and wettability to achieve the non-backflow fracturing-strong wetting effect for coal seam water injection. The optimal hydraulic fracturing fluid exhibits high viscosities up to 300 mPa·s and good shear stability for at least 2 h, which meets the industry standards for practical applications. Lubricant, a mixture of hydrocarbons including alkanes, cycloalkanes, aromatics, etc., was found to be an excellent gel breaker, which left <50 mg/l gel residue after the gel breaking, and thus endowed the hydraulic fracturing fluid the cleanness properties for coal seam water injection. The high wettability of the gel breaking solution on coal seam was demonstrated with its contact angle of 20° smaller than that of water on average. Our study has provided a scientific foundation for the application of VES fracturing fluids to coal seam water injection.