多簇压裂干扰应力变化规律及对裂纹扩展的影响

为研究水平井分段多簇压裂缝间的干扰应力及其对裂纹扩展的影响，在现有二维未考虑地应力的单裂缝干扰应力解析解的基础上，利用双平面复变函数保角变换得到了包含地应力项的三维干扰应力解析解。基于扩展有限元法建立三维多裂缝扩展力学模型，利用Python脚本二次开发平台实现了三维多裂缝水力压裂参数化建模，通过解析解与数值计算对比分析，得到如下结论。裂纹两侧裂纹面法向和走向干扰正应力分别为压应力和拉应力，均呈纺锤形，法向干扰应力影响范围大约为走向干扰应力的5倍；裂纹尖端裂纹面法向和走向干扰正应力分别为拉应力和压应力；裂纹尖端两侧存在干扰剪应力；考虑初始地应力对干扰应力解析解进行修正后的干扰应力值均变小；多簇压裂中裂缝间的干扰应力叠加，簇间距越小，叠加效果越强；多簇压裂的干扰应力使裂缝间裂纹面法向压应力增大，走向压应力减小，导致裂纹扩展注水压力升高，裂缝张开的宽度降低，不利于单裂缝的扩展；干扰应力使裂缝间应力差降低，甚至局部最小地应力方向发生改变，有利于形成复杂缝网。

Law of induced stress in multi-cluster fracturing and the effect on crack propagation

In order to study the induced stresses in multi-cluster cracks of horizontal wells and their effects on crack propagation,an analytical solution of 3D induced stresses considering in-situ stresses was established by double plane complex variable function conformal transformation based on 2D induced stress solutions without in-situ stress.A 3D multiple-crack propagation parametric numerical simulation was realized by Abaqus/Python and the extended finite element method.This research drew the following conclusions through analytical derivation and numerical analysis.The induced stresses beside on the crack faces have vertical compressive stress and tangential tensile stress and both are spindle shaped.The vertical induced stress influence range is about 5 times of the tangential.In contrast,the induced stresses around a crack tip have vertical tensile stress and tangential compressive stress.The induced shear stress appears beside a crack tip.The modified analytical solution of streeses after taking in-situ stress into consideration becomes lower.The induced stresses add up in multi-cluster fracturing and the combined effects get stronger along the cluster space crack.The superposed induced stresses make the crack expand and fluid pressure rise and the crack opening reduces which restricts the propogation of a single crack.The induced stress effects reduce the stress difference and change the dreictions of the minimum stresses at some positions,which can promote formation crack network.