水中高压电脉冲作用下径向预制裂纹扩展规律

Propagation of Radial Prefabricated Crack under High Voltage Electric Pulse in Water

为研究水中高压电脉冲作用下页岩多条预制裂纹同步扩展应力干扰作用对裂纹扩展影响,通过裂纹扩展轨迹、扩展长度、平均宽度、偏转角度和裂纹间等效应力分布的变化规律,综合考虑裂纹夹角、裂纹数量、水平地应力差等因素对裂纹起裂、扩展的影响。采用真三轴高压脉冲水力压裂试验平台进行实验室压裂试验和扩展有限元法(extended finite element method, XFEM)数值模拟计算,利用PCAS(pore and cracks analysis system)裂隙分析软件分析裂纹几何形态特征。结果表明:水中高压电脉冲作用下,预制裂纹可沿径向及轴向起裂、扩展;径向双裂纹间夹角越大,缝间干扰作用越弱,裂纹扩展曲折程度越好,扩展效果越好;等夹角径向三裂纹扩展,中间裂纹受应力干扰、受抑制作用最大,不等夹角径向三裂纹扩展,远离中间裂纹的右侧裂纹受干扰最小,扩展效果最好;随着水平地应力差增加,裂纹间应力干扰作用增强,裂纹扩展效果逐渐减弱。研究成果可为分析水中高压电脉冲作用下页岩多预制裂纹扩展过程和规律提供一定的参考。

In order to study the effect of stress interference on the synchronous propagation of multiple prefabricated cracks in shale under the action of high-voltage electrical pulses in water,the change law of crack propagation trajectory,propagation length,average width,deflection angle,and equivalent stress distribution between cracks was studied,the effects of crack angle,crack number,horizontal ground stress difference and other factors on crack initiation and propagation were comprehensively considered.The triaxial high-pressure pulse hydraulic fracturing test platform was used for laboratory fracturing test and extended finite element method(XFEM)numerical simulation calculation,the pore and cracks analysis system(PCAS)crack analysis software was used to analyze the geometric characteristics of cracks.The results show that under the action of high voltage electric pulse in water,the pre cracks start and expand along the radial and axial directions.The larger the included angle between the radial double cracks is,the weaker the interference between the cracks is,and the worse the crack propagation effect is.Three radial cracks with equal included angle propagate,and the middle crack is the most disturbed and restrained by stress,while the three radial cracks with unequal included angle propagate,and the right crack far away from the middle crack is the least disturbed and the propagation effect is the best.With the increase of the horizontal in-situ stress difference,the stress interference 9 between cracks is enhanced,and the crack propagation effect is gradually weakened.The research results can provide a certain reference for analyzing the process and laws of multiple prefabricated cracks propagation in shale under the action of high-voltage electric pulses in water.