INFLUENCE OF DIFFERENT SCALES OF STRUCTURAL PLANES ON PROPAGATION MECHANISM OF HYDRAULIC FRACTURING

In shale gas reservoirs, natural rock mass structural planes usually have significant influences on hydraulic fracturing treatment. This study uses the RFPA2D-Flow program. It considers the coupling seepage-stress-failure process of crack initiation, propagation, and damage. It simulates hydraulic fracturing process of rock mass in heterogeneous rock mass with different scales of natural structural planes. Though numerical simulation and discussion, the main conclusions can be drawn as follows:(1) When a hydraulic fracture encounters a natural unclosed crack, the principal stress trajectories would be deflected and a tensile stress zone would be created between the hydraulic fracture and the natural crack due to the increased pore pressure and propagation of the hydraulic fracture. Thus, the emergence and coalescence of tensile failure of the micro-units eventually causes the connection between the hydraulic fracture and the natural crack.(2) Bedding planes have pronounced effects on hydraulic fracturing. When the strikes of the maximum principal stress and the bedding planes intersect at a small angle, the bedding planes control the propagation of the hydraulic fractures. Otherwise, both the maximum principal stress and the bedding planes dominate the expansion of the fracture network. In addition, with the increase in structural planes and differential stresses, the scope and complexity of the stimulated fracture network increase simultaneously.(3) Hydraulic fracturing treatment is a short dynamic damage process. Although the existing of a fault structure can greatly affect the propagation model of the hydraulic fracturing and enhance the growth height of the hydraulic fracture, the damage to fault sealing capacity and activity caused by hydraulic fracturing is still limited compared with the depth of the reservoir.