Study on the Three Dimensional Fracture Propagation in Shale Oil Reservoirs with Multiple Horizontal Bedding Planes

Abstract

Abstract As an unconventional resource, shale oil is extensively buried in the Sichuan Basin. The shale oil reservoirs have a large number of horizontal bedding planes with weaker strength, and the existence of bedding planes may suppress the growth of fracture height, leading to insufficient stimulation of reservoirs. Understanding the influence of bedding planes on vertical fracture propagation is crucial for engineers to know exactly how the fracture morphology is. In this paper, true triaxial experiment and 3D block DEM method are both adopted to investigate the propagation law of fractures in shales. The accuracy of the numerical model is verified by fracturing experiments. This paper quantitatively evaluates the effect of geological and engineering parameters from calculated area of main fracture and activated bedding planes, and the mechanism of HF/BP interaction is analyzed. The experimental results show that the generated fracture is characterized by rough fracture surface and asymmetric propagation. The increase of injection rate is beneficial to the occurrence of penetration, and the development degree of bedding plane obviously affects the height growth of hydraulic fracture. The numerical results indicate that the hydraulic fracture tends to penetrate the bedding planes under the condition of higher vertical stress, higher cohesive strength of bedding plane, higher fluid viscosity, and higher displacement. Due to the influence of bedding planes, the fracture morphology is complex, mainly including "キ", "工", and "I" shape. The cohesive strength of bedding plane has significant impact on fracture propagation, and the tensile strength of bedding plane almost have no effect on fracture propagation. For shale reservoirs with well-developed bedding planes, the oriented perforation technology combined with deeply penetrated perforation bullets is recommended to be applied to improve the penetration ability of fracture. On the other hand, a high-viscosity fluid is recommended to be used to increase the fracture height, and then low-viscosity slick water is used to increase the bedding activation, thereby achieving effective spatial stimulation of reservoirs. According to the research results, a reverse hybrid pumping method is applied in Well L1, and ideal stimulating effect has been obtained. This paper provides an effective method for accurately simulating the vertical propagation of fractures in shale reservoirs with multiple bedding planes, deepen the engineers' understanding of the factors affecting the fracture morphologies, and help them optimize the fracturing parameters of shales.