射孔对井眼围岩应力场及破裂压力影响规律

Influence of Perforation on the Wellbore Surrounding Rock Stress and Fracture Pressure

射孔在一定程度上可以有效地降低地层破裂压力,避免裂缝扭曲和多裂缝的不利现象;射孔参数的改变会导致井壁围岩应力场及破裂压力的改变,进而影响压裂施工和压后产能。加强射孔井井壁围岩应力场的动态演化规律研究,对指导水力压裂施工、井壁稳定性、储层改造等具有重要的意义。利用ABAQUS有限元计算软件建立套管-水泥环-地层的三维数值模型,在考虑流固耦合效应和动态效应的基础上,运用单一变量理论对不同的射孔密度、射孔长度、射孔方位角等射孔参数进行模拟分析,得到井壁围岩应力分布及水力压裂破裂压力的定性认识并给出最优的射孔参数。研究结果可为压裂井射孔工艺技术优化设计提供一定的理论指导。

The perforation, to a certain extent, can effectively reduce the formation fracture pressure to avoid cracked distortions and muhiple fractures. And the perforation parameters are related with the borehole wall surrounding rock stress and the fracture pressure, thereby, the fracturing pressure capacity and the dynamic evolution of the perforation shaft wall surrounding rock stress field are important issues for the hydraulic fracturing operation, the wellbore stability, and the reservoir reconstruction. In this paper, firstly, using the finite element analysis software ABAQUS, a three-dimensional numerical model of the casing-cement ring-formation is established to study the fluid-structure coupling effects and the dynamic effects. A qualitative understanding of the borehole wall surrounding rock stress distribution and the hydraulic fracturing breakdown pressure is achieved and the optimal perforating parameters are obtained by the numerical simulation on the basis of the single variable theory for the perforation parameters, including the perforation density, the perforation length, and the perforation azimuth. The results provide some theoretical guidance for the fractured well perforating technology optimization design.