Hydraulic fracture patterns in fractured rock mass using coupled hydromechanical modeling in the bonded particle model

The present study aimed to simulate the interaction between hydraulic fractures and natural fractures using hydromechanical coupling in the bonded particle model using the smooth joint method, followed by sensitivity analysis regarding the angle of approach of the pre-existing fractures relative to the direction of the hydraulic fracture, strength of the natural fractures, and ratio of the in-situ stresses. In the present research, the model of hydraulic fracture in a reservoir with natural fractures was assessed by hydromechanical coupling, implemented in the discrete element method, based on the BPM. Considering the discontinuous nature of the current research, the BPM-based PFC2D software was applied to simulate the interaction of hydraulic fractures and natural fractures. At first, the microparameters that correspond to the macroscale characteristics of the rock were identified by comparison with experimental results through repetitive calibration. DEM results were compared with experimental results from uniaxial compressive and Brazilian test scale model testing. Sensitivity analysis was performed in terms of the angle of approach parameters of natural fractures, joint strength, and in-situ stress ratio. According to the results of the modeling processes, the shape of the time history curves of wellbore pressure was the same for various angles of approach of 30, 60, and 90 degree relative to the vertical direction. Since the hydraulic fracture tended to be grown and propagated in the direction of the least strength, it propagates in the pre-existing fractures without strength or their dilation. The hydraulic fracture breakdown largely depended on the ratio of the in-situ stresses as in a similar state of the maximum principal stress, the value of the minimum principal stress had considerable effects on the fracture propagation pattern. The breakdown pressures of the hydraulic fracture with the increased heterogeneity and ratio of the in-situ stresses decreased in a similar situation of the value of the maximum principal stress. The modeling results indicated that the hydraulic pressure and onset of breakdown time largely depended on the value of the minimum principal stress, so that the increased minimum principal stress would increase the hydraulic fracture and onset time of fracturing. The hydraulic fracture pattern depended on in-situ stresses, and the higher in-situ stress ratios were associated with the increased length of the fracture experiencing aperture.