基于PHF-LSM模型岩石分段水力压裂应力阴影效应

采用PHF-LSM(permeability-based hydraulic fracture-level set method)水力压裂数值计算模型，模拟并分析了均质与分层岩石材料中分段压裂过程引起的应力阴影效应.通过与单一裂缝诱发应力理论解的对比，验证了PHF-LSM考虑应力阴影效应的可行性.以此模型为基础分析了单一裂缝发展过程中，岩石材料参数与初始应力条件对诱发应力场的影响，以及均质与分层岩石材料的多裂缝起裂过程中不同压裂间距与压裂顺序产生的应力阴影效应.数值计算结果表明:泊松比、抗拉强度与孔隙率的增加会增大裂缝引起的诱发应力与净压力比值的峰值，而弹性模量和水平主应力差的增大会减小该峰值；裂缝间距的扩大可以减弱裂缝间应力阴影效应；两步压裂与顺序压裂的裂缝总面积均大于同时压裂时的面积，但顺序压裂与两步压裂会带来更高的起裂压力；产层厚度与压裂间距的减小会增大应力阴影效应.

The Stress Shadow Effect of Multistage Hydraulic Fracturing of Rock Material Based on PHF-LSM Model

The PHF-LSM(permeability-based hydraulic fracture-level set method)hydraulic fracturing numerical model is used to simulate and analyze the stress shadow effect caused by staged fracturing in homogeneous and layered rock materials. Compared with the theoretical solution of single crack induced stress， the feasibility of considering stress shadow effect in PHF-LSM is verified. Based on this model， the influence of rock material parameters and initial stress conditions on induced stress field during the development of single fracture， and the stress shadow effect caused by different fracturing spacing and fracturing sequence during the initiation of multiple fractures in homogeneous and layered rock materials were analyzed. The numerical results show that the increase of Poisson′s ratio， tensile strength and porosity will increase the peak value of the ratio of induced stress to net pressure， while the increase of elastic modulus and horizontal principal stress difference will decrease the peak value. The expansion of crack spacing can weaken the stress shadow effect between cracks. The total fracture area of the two-step fracturing and the sequential fracturing are larger than that of simultaneous fracturing， but sequential fracturing and two-step fracturing will cause higher fracture initiation pressure. The decrease of pay layer thickness and fracturing spacing will increase the stress shadowing effect.