Effect of Reservoir Transformation on Fracture Expansion in Deep Coalbed Methane Reservoirs and Mechanism Analysis

This paper proposed a fracture propagation model of water-based fracturing based on seepage–stress–damage coupling, which was employed to analyse the effects of different water-based fracturing fluid properties and rock parameters on the propagation behaviour of reservoir fractures in low-permeability reservoirs. Concurrently, molecular dynamics theory and mechanical analysis of reservoir fractures were employed to elucidate the microscopic mechanism of water-based fracturing on fracture propagation. The results showed that the apparent viscosity of water-based fracturing fluid primarily contributed to elevated fracture internal pressures through the seepage reduction in water-based fracturing fluid at the coal fracture surface. A substantial impact on the minimum fracturing pressure of coal fractures that rapidly pierce the coal rock and an increasing crack extension was notably presented by the low filtration and high viscosity of water-based fracturing fluids. Furthermore, the reservoir pressure and the crack turning angle were not conducive to the effective expansion of coal seam fractures, whereas the reservoir temperature exhibited a positive proportional relationship with deep coal seam fractures.