Exploration of non-planar hydraulic fracture propagation behaviors influenced by pre-existing fractured and unfractured wells

Hydraulic fracturing plays significant role in enhancing production performance of low-porosity and low-permeability reservoirs because the created hydraulic fracture (HF) can improve the communication between formation and wellbore. Therefore, understanding propagation behaviors of HF is critically important for the design of hydraulic fracturing treatment. Normally, HF tends to take a straight path in a symmetrical stress field when rockmass is homogeneous and isotropic. However, as a result of fluid injection or production through pre-existing wells, non-uniform stress field can be encountered during the fracturing treatment in which case HF will be deviated along the perturbed principal stress field in the formation. In this work, to investigate the effects of adjacent fractured and unfractured wells on HF propagation, a new numerical model is developed within the framework of extended finite element method (XFEM) and cohesive zone method (CZM). The model can simultaneously capture HF initiation, propagation and re-orientation, fracturing fluid flow and leakoff, formation fluid flow and rock deformation. The results indicate that HF is attracted towards pre-existing injection well with deviation angle being larger when the injection well is fractured, whereas HF tends to deviate away from offset production well with deviation angle being larger around fractured production well. Meanwhile, the pre-existence of injection well makes the HF wider, and longer HF can be created near the production well. The results also demonstrate that both breakdown pressure (BDP) and fracture propagation pressure (FPP) are increased around the pre-existing injection well while BDP and FPP are decreased near the offset production well. The obtained conclusions provide new insights for understanding the HF propagation problem in the field scale.