深度对含瓦斯煤层水力压裂裂纹转向行为的影响数值模拟分析
Numerical simulation analysis of influence of depth on crack turning behavior in hydraulic fracturing of gas-bearing coal seam
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摘要: 随着深度的增加，煤岩层受到的水平应力与垂直应力之比会逐渐降低，进而对水力压裂注压孔周围的裂纹扩展行为造成影响。为了探究不同深度下水力压裂裂纹转向行为特征，基于煤层力学模型与瓦斯吸附动力学模型，利用多物理场耦合模拟软件COMSOL进行分析，获得了不同深度条件下注压孔周围的应力分布特征以及裂纹起裂压力特征。结果表明：在较浅的深度，即水平应力与垂直应力比值大于1时，裂缝主要在水平方向上扩展，且应力比值增大，裂缝越容易发生转向；而在较深的深度，即水平应力与垂直应力之比小于1时，裂缝在向垂直方向上延伸，且应力比值越小，裂缝越容易发生转向。Abstract: As the depth increases, the ratio of horizontal to vertical stress on the coal rock strata will gradually decrease, which affects the crack propagation behavior around hydro-fracture injection hole. In order to explore the characteristics of hydro-fracture crack turning behavior at different depths, based on the mechanical model and adsorption and desorption model of coal seam, COMSOL was used to analyze the stress distribution and crack initiation pressure around the injection hole at different depths. The results show that at shallow depths, the ratio of horizontal stress to vertical stress is greater than 1, the cracks extend mainly horizontally, and the fracture is more likely to turn when the stress ratio increases. At a deeper depth, the ratio of horizontal stress to vertical stress is less than 1, the cracks extend mainly vertically, and the fracture is more likely to turn when the stress ratio decreases.
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