Hydraulic fracturing is the best method to improve production in deep shale, and the complex natural fracture affects the fracture propagation. In this study, numerous true tri-axial experiments were conducted on hydrostone to study the effect of the natural fracture complexity. The position and the relative angle of natural fracture were mainly studied. The acoustic emission was used to detect the fracture propagation and the pumping curve was analyzed. The results showed that the three-dimensional fracture morphologies can be classified into five ways: arresting, bypassing, crossing, vertical extension and slipping. Symmetrical natural fracture around the wellbore helped to increase the fracture height extension. When natural fractures distributed asymmetrically, the hydraulic fracture showed obvious single wing crack. The hydraulic fracture tended to activate the natural fracture and changed direction along the natural fracture with a small approaching angle. The pumping curve rising in the propagation stage showed the fracture arresting the natural fracture. More complex fracture network corresponded to more fluctuated curve. The results give a deep understanding of the effect of the natural fracture complexity in 3D and help to predict the fracture intersection morphology in the field.

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