Research on Fracture Initiation Mechanisms of Hydraulic Fracturing Guided by Multi-radial Boreholes

Abstract

At present, the technology of hydraulic fracturing guided by radial boreholes has gradually been applied to the development of low permeability reservoirs, but the related fracture initiation mechanism is insufficient. In order to clarify the fracture initiation mechanism under the guidance of radial boreholes, it is necessary to study the stress distribution around wellbore with the existence of radial boreholes. The effects of in situ geo-stress, wellbore internal pressure and fracturing fluid percolation effect on geo-stress field distribution are taken into account, a mechanical model of multi-radial boreholes with any number, vertical depth and azimuth angle (the angle between the radial borehole and the horizontal maximum geo-stress) is established. By using Matlab to carry out sample analysis of the model, the influence of various parameters on the maximum principal stress have been studied, and the fracture initiation position has been predicted by combining with tensile fracture criterion. Studies have shown that the maximum principal stress increases with the increase of the horizonal geo-stress difference and the diameter of the radial borehole. When the horizonal geo-stress difference is small, the maximum principal stress increases first and then decreases with the increase of the azimuth angle; when the horizonal geo-stress difference is large, the maximum principal stress decreases with the increase of the azimuth angle. When multi-radial boreholes existing, the maximum principal stress increases with the increase in the number of radial boreholes and the decrease in the vertical spacing between radial boreholes. The maximum principal stress generally decreases as the phase angle (angle between radial boreholes) increases, but anomalous phenomena occur when the horizonal geo-stress difference is small and the radial borehole diameter is large. This study provides theoretical support for guiding fracture by multi-radial boreholes. In order to make the radial boreholes better guide the fracture, the optimal design should be optimized by optimizing the azimuth angle of the borehole, increasing the diameter of the borehole, reducing the borehole spacing, increasing the number of radial boreholes, and reducing the phase angle between boreholes.