Numerical modelling of fracturing effect stimulated by pulsating hydraulic fracturing in coal seam gas reservoir

Abstract

Pulsating hydraulic fracturing (PHF) technology is an advanced permeability enhancement method for coal seam gas mining. Laboratory and field experiments indicate that PHF can stimulate a well-distributed fracture system inside a coal reservoir. However, the basic mechanism behind this effect is still poorly understood. In this study, a better mathematical model for pressure ripple propagation is proposed and an analytical solution is obtained. Furthermore, the particle flow code is applied based on the analytical solution to numerically simulate the fracturing effect of PHF. The mechanism for fracture system formation with the original coal cleat system is quantitatively analysed by using advanced indicators (crack event density, crack intensity rate and kinetic energy). A new cracking pattern is proposed and discussed. Eventually, fracturing effects under different engineering PHF inputs (i.e., pulsating frequency and ripple amplitude) are numerically simulated and analysed. The conclusions build a theoretical basis for the mechanism of PHF effect. The PHF parameters may also be largely improved and optimized for the extension and formation of fracture networks in a coal seam gas reservoir.