Research on the Distribution Law of Fault Slip Based on Finite Element Simulation

The economic exploitation of tight shale formations necessitates the utilization of hydraulic fracturing operations. However, during the hydraulic fracturing process, the issue of casing deformation becomes particularly pronounced. The severe casing deformation significantly impedes the smooth execution of fracturing operations. Based on field data, approximately half of the casing deformation instances are considered to have a strong correlation with fault slippage. According to classical fault slip theory, when the fracturing fluid enters the fault during fracturing operations, it leads to a reduction in the effective normal stress on the fault plane (reduction of the upper limit of frictional force), thereby causing fault slippage and resulting in casing deformation. However, the current theories cannot well explain the cases where only some wells crossing the same fault experience deformation, and the distance between the deformation points and the hydraulic fracturing operations position is relatively far. This paper establishes a hydraulic fracturing crack propagation model with a fault using the Extended Finite Element Method. The influence of hydraulic fracture propagation on the fault during the fracturing process is analyzed. The results indicate that different from classical theories, only partial regions of such faults experience slip. Furthermore, the simulations also revealed that even in the absence of hydraulic fracturing fluid communication with the fault, a mere alteration in the shear stress within the fault zone alone may still lead to localized fault displacement. These two phenomena discovered through simulations can better explain the actual mechanisms underlying partial casing deformation.