基于位移相关法的重复压裂裂缝尖端应力场研究

Research on stress field at the top of fracture during refracturing based on displacement correlation method

黄炳庆 樊军 高鹏

新疆大学机械工程学院，新疆 乌鲁木齐 830047

School of Mechanical Engineering, Xinjiang University, Urumqi 830047, China

重复压裂技术是低渗透油田、非常规油气藏增产增效的重要措施，利用再加压打开储层的油气通道，可获取更高的开采量。新裂缝的起裂及延伸规律对重复压裂效果评价至关重要。从力学角度分析，裂缝的起裂及延伸与裂缝尖端应力强度息息相关。在饱和多孔介质固体骨架的平衡方程、流体力学和地质力学控制方程的基础上，考虑初始流体密度和孔隙度、地应力、初始孔隙压力等因素的影响，建立了适用于目标油井的储层流固耦合数学模型。以单元节点位移和单元节点孔隙压力为未知量，对该模型进行时间域有限元离散，导出了储层流固耦合的非线性有限元增量方程。根据求解的位移值、应力和应变，基于有限元软件平台利用位移相关法求解裂缝尖端应力强度因子，进行实例分析，验证了所建模型的有效性。

Refracturing technology is an important method to stimulate and beneficiate low permeability oilfields and unconventional hydrocarbon reservoirs. By recompression, we can open the channel of oil and gas in the reservoir and obtain high exploitation quantity. The initiation and elongation law of new fracture is essential to refracturing evaluation. From the perspective of mechanics, the initiation and elongation of new fracture are closely related with the stress intensity at the top of fracture. In this paper, based on the equilibrium equation of solid skeleton and control equations of fluid mechanics and geotechnical, the influencing factors such as initial fluid density, initial porosity, in situ stress and initial pore pressure are taken into account. A mathematical model for fluid-solid coupling for the reservoir suitable for target well is established. Finite element discretization is carried out on the mathematical model to get a fully coupled finite element equation with the parameters of element nodal displacement and element nodal pore pressure as unknown variables. According to the displacement stress and strain values solved before, finite element software platform is adopt to calculate the stress intensity factor based on the displacement correlation method. Finally, an example is carried out to verify the validity of the model.

10.6056/dkyqt201405028