Hydraulic fracturing of reservoirs containing rough discrete fracture networks: FDEM-UPM approach

Fractures are typically characterized by roughness that significantly affects the mechanical and hydraulic characteristics of reservoirs. However, hydraulic fracturing mechanisms under the influence of fracture morphology remain largely unexplored. Leveraging the advantages of the finite-discrete element method (FDEM) for explicitly simulating fracture propagation and the strengths of the unified pipe model (UPM) for efficiently modeling dual-permeability seepage, we propose a new hydro-mechanical (HM) coupling approach for modeling hydraulic fracturing. Validated against benchmark examples, the proposed FDEM-UPM model is further augmented by incorporating a Fourier-based methodology for reconstructing non-planar fractures, enabling quantitative analysis of hydraulic fracturing behavior within rough discrete fracture networks (DFNs). The FDEM-UPM model demonstrates computational advantages in accurately capturing transient hydraulic seepage phenomena, while the asynchronous time-stepping schemes between hydraulic and mechanical analyses substantially enhanced computational efficiency without compromising computational accuracy. Our results show that fracture morphology can affect both macroscopic fracture networks and microscopic interaction types between hydraulic fractures (HFs) and natural fractures (NFs). In an isotropic stress field, the initiation azimuth, propagation direction and microcracking mechanism are significantly influenced by fracture roughness. In an anisotropic stress field, HFs invariably propagate parallel to the direction of the maximum principal stress, reducing the overall complexity of the stimulated fracture networks. Additionally, stress concentration and perturbation attributed to fracture morphology tend to be compromised as the leak-off increases, while the breakdown and propagation pressures remain insensitive to fracture morphology. These findings provide new insights into the hydraulic fracturing mechanisms of fractured reservoirs containing complex rough DFNs. • A new hydro-mechanical coupled model was proposed by leveraging the advantages of FDEM for modeling fracture propagation and the strengths of UPM for simulating dual-permeability seepage. • The proposed FDEM-UPM model is enriched by a Fourier-based methodology for quantitatively reconstructing fracture profiles and a customized sampling criterion for stochastically generating rough DFNs. • The influence of fracture morphologies on hydraulic fracturing behavior are revealed, which provides new insights into the hydraulic fracturing mechanisms of fractured reservoirs containing complex rough DFNs.