关键词: 煤层, 脉动水力压裂, 交错网格, 动静态响应, 参数优化

Abstract: Pulsating hydro-fracturing (PHF) is a new technique on substantially increasing permeability in coal seam. However, few studies have considered the stress propagation and distribution of PHF in real formation. Combining with perfectly matched layer (PML) absorptive boundary and quasi-static confining loading technique, staggered-grid high-order difference numerical method is used to establish a dynamic and static response numerical model in infinite elastic formation with confining pressure. The peak value distribution of minor principal stress is investigated with different loading styles, confining pressures, frequencies, and amplitudes. Numerical results indicate that the transmission and interference effect of stress wave are the dominant factors which make the permeability-enhanced area of PHF is much larger than that of conventional fracturing. The frequency and amplitude are directly proportional to the PHF effect, but only the amplitude overtops a threshold value controlled by confining pressure, the permeability-enhanced area can be brought; the confining pressure is inversely proportional to the PHF effect, and the second principal stress is the dominant factor. When the second principal stress decreases from 3.5 MPa to 2.0 MPa, the permeability-enhanced area will increase 600% at most. Based on this numerical model, the dynamic and static stress response of PHF and conventional fracturing can be investigated, and its results will provide guidance to optimize the PHF technological parameters.

Key words: coal seams, pulsating hydro-fracturing, staggered grid, dynamic and static response, parameters optimization