Numerical investigation of interaction between hydraulic and natural fractures under various geologic and engineering parameters using particle flow code method

Abstract

ABSTRACT Gaining a better understanding on the mechanism of the interaction between the hydraulic fracture (HF) and the natural fracture (NF) is essential for increasing the stimulated reservoir volume (SRV) of shale gas fracturing. In this study, a two-dimensional (2D) numerical model for simulating the behavior of HF/NF interaction using particle flow code (PFC) method was established, and this model can consider the fluid-mechanical coupling effect, the fluid flow in permeable NFs, and the heterogeneity of particle size. The numerical model was verified by KGD analytical model and Gu and Weng’s analytical model. The input micro-parameters for PFC simulation were calibrated to match with the experimental macro-parameters of Longmaxi shale by trial-and-error method. The effects of various geologic and engineering parameters on the HF/NF interaction were investigated using PFC method. The modeling results show that there are six kinds of HF/NF interaction patterns observed from the results of PFC simulation. The HF will hardly cross the NF directly when the permeability of NF reaches a higher value of 100 mD. When the in-situ stress difference reaches 13 MPa, the HF will cross the NF even if the other factors are not favorable to the occurrence of “crossing”. The product of injection rate and fracturing fluid viscosity (Q·μ) is suggested to be used to study the HF/NF interaction, and the HF tends to cross the NF under a higher value of Q·μ. Moreover, the scenario of “crossing” is extremely likely to occur under orthogonal approach angle, and frictional coefficient of NF has little effect on orthogonal HF/NF interaction. The cases with the same HF/NF interaction pattern have a similar variation trend of borehole pressure history curve. Through analyzing the numerical results, the technical measures such as variable pump rate fracturing method and alternate injection method of slickwater-linear gel fluid were suggested to be applied to increase the complexity of fracture network. Abbreviation 2D: Two-dimensional; 3D: Three-dimensional; PFC: Particle flow code; EIA: Energy Information Administration; SRV: Stimulated reservoir volume; BPM: Bonded particle model; PBM: Parallel bond model; FEM: Finite element method; BEM: Boundary element method; DEM: Discrete element method; XFEM: Extended finite element method; CZM: Cohesive zone model; UDEC: Universal distinct element code; 3DEC: Three-dimensional distinct element code; DDM: Displacement discontinuity method; SJM: Smooth joint model