Natural fracture opening pressure in the ultra-deep reservoir considering friction resistance along the hydraulic fracture

ABSTRACT: In the process of hydraulic fracturing, hydraulic fractures can activate natural fractures and form a complex fracture network, but the opening of natural fractures needs to reach a certain threshold pressure (i.e., opening pressure). In ultra-deep reservoirs, the width of hydraulic fractures is small. If the flow friction of fracturing fluid in hydraulic fractures is ignored, the calculation of opening pressure will bring large errors. In this study, the opening pressure was calculated considering the combined effect of the friction along the hydraulic fractures and the local in-situ stress of the natural fracture. A mathematical model of natural fracture opening pressure considering the flow friction is proposed. Through the example calculation and analysis, it is found that the opening pressure of ultra-deep natural fractures is most affected by the width of hydraulic fractures, and due to the high stress difference, natural fractures are easier to be opened by shear slip. The longer the hydraulic fracture and the narrower its width, the greater the friction of the fracturing fluid along its path, which leads to a higher opening pressure for natural fractures. The high viscosity of the fracturing fluid and the large flow rate also increase the opening pressure of the natural fracture.