【摘要】 煤层脉动水力压裂是一项大范围提高煤层渗透率的新技术,但针对脉动应力波在实际地层的传播、扰动规律研究较少。采用交错网格数高阶有限差分法,结合完全匹配层和准静态围压加载两种边界条件,建立了含围压无限大弹性地层脉动水力压裂动静态响应数值模型,并研究了不同加载方式、频率、振幅、围压条件下煤层最小主应力峰值分布规律。研究表明:由于应力波传播及干涉效应,相同围压、振幅条件下脉动压裂增透扰动区域远大于准静态压裂;煤层增透面积随震源频率和振幅的增加而增大,振幅需要克服由围压控制的启动压力才能产生增透区;增透面积与地层主应力成反相关且最小主应力起主导作用,其由3.5 MPa下降至2.0 MPa时,增透面积最高可提升600%。模型可模拟准静态和脉动加载下煤层的力学响应,其结果可为优化脉动水力压裂工艺参数提供指导。更多还原

【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.更多还原