水力压裂多裂缝扩展的近场动力学模拟

Peridynamics Simulation of Multi-fracture Propagation in Hydraulic Fracturing

为研究页岩水力压裂中多裂缝扩展规律,采用一种结合近场动力学和有限差分法的方法对水力压裂问题建立流固耦合模型。使用近场动力学建立单相固体平面应力问题模型,采用达西定律描述裂隙内流体和基质内流体的流动,对流动区域以损伤程度进行划分,并通过损伤值标定对应的渗透率,采用有限差分法求解得到渗流场压力分布,依据有效应力原理得到流固耦合模型。设计了不同间距的两条裂缝,交错的两条裂缝与三条裂缝同时扩展的模拟实验。结果表明,由于缝间干扰,两条裂缝扩展时会发生反向偏转,并且随着裂缝间距减小,偏转越明显;对于两条交错裂缝,随着裂缝扩展,会互相吸引;对于三条裂缝扩展的情况,中间裂缝的扩展会受到限制。可见需要适当增大水力裂缝间距,减小缝间干扰的影响。

In order to study the propagation law of multi-fracture in shale hydraulic fracturing, a combination of peridynamics and finite difference method was used to establish a fluid-solid coupling model for hydraulic fractures. Peridynamics was used to model the single-phase solid plane stress problem, Darcy’s law was used to model the flow of fluid in hydraulic fractures and matrix, the flow area was divided by the degree of damage and calibrate the corresponding permeability by damage value, finite difference method was used to solve the pressure distribution of seepage field, obtain the fluid-solid coupled model based on the principle of effective stress. A simulation experiment of two hydraulic fractures with different spacing, two staggered hydraulic fractures and three hydraulic fractures was designed. The results show that due to the interference between cracks, the reverse deflection will occur when the two cracks expand, and the deflection becomes more obvious as the crack spacing decreases. For two staggered cracks, as the cracks expand, they will attract each other. For the case of three cracks, the expansion of the middle crack will be limited. It can be seen that it is necessary to appropriately increase the spacing of hydraulic cracks and reduce the influence of interference between cracks.