Analysis of Fracture Morphology and Propagation Mode of Shale Oil Reservoir Based on Triaxial Hydraulic Fracturing Simulation Experiment

In this paper, through the triaxial hydraulic fracturing simulation experiment, the fracture morphology of outcrop rock mass in shale oil reservoir under different displacement, different surrounding rock pressure, different pumping process and different natural fracture development is accurately described, and four main characteristics of fracture propagation in shale oil reservoir are summarized: (1) The higher the surrounding rock pressure, the more difficult the fracture cracking and the simpler the fracture network. After preferentially forming fractures through the bedding plane, high surrounding rock pressure has a great obstacle to crack opening and charging on the parallel bedding plane. (2) The step displacement crushing of rock is beneficial to forming fractures through the bedding plane in multiple directions, and is easier to open and fill in the horizontal bedding plane, forming a multi-direction fracture network with more excellent seepage surface. (3) High-displacement charging is hindered greatly in the direction of cross-bedding, and it is easier to show shear failure in the direction of horizontal bedding after extending to a certain scale, and the failure surface is relatively flat; Low displacement charging has more pressure holding time and higher fracture pressure in the direction of cross-bedding, but the fracture charging ability is weak, and it is difficult to form a large fracture surface in the direction of horizontal bedding. (4) The shale with natural fractures is easy to form complex fracture network in the direction of vertical fracture plane, and large fracture plane in the direction of cross bedding and parallel bedding. The main influencing factors of fracture displacement, in-situ stress, bedding surface and natural fractures on fracture propagation direction and scale are revealed, which determine fracture propagation mode of shale oil reservoir. It is concluded that the fracturing operation with small displacement and rated pump pressure immediately after the wellbore fracture has the potential to obtain complex fracture network, thus greatly improving the reservoir reconstruction effect.