Abstract
Conventional hydraulic fracturing is not effective in target oil development zones with available wellbores located in the azimuth of the non-maximum horizontal in-situ stress. To some extent, we think that the radial hydraulic jet drilling has the function of guiding hydraulic fracture propagation direction and promoting deep penetration, but this notion currently lacks an effective theoretical support for fracture propagation. In order to verify the technology, a 3D extended finite element numerical model of hydraulic fracturing promoted by the single radial borehole was established, and the influences of nine factors on propagation of hydraulic fracture guided by the single radial borehole were comprehensively analyzed. Moreover, the term ‘Guidance factor (Gf)’ was introduced for the first time to effectively quantify the radial borehole guidance. The guidance of nine factors was evaluated through gray correlation analysis. The experimental results were consistent with the numerical simulation results to a certain extent. The study provides theoretical evidence for the artificial control technology of directional propagation of hydraulic fracture promoted by the single radial borehole, and it predicts the guidance effect of a single radial borehole on hydraulic fracture to a certain extent, which is helpful for planning well-completion and fracturing operation parameters in radial borehole-promoted hydraulic fracturing technology.
Highlights
The term radial borehole refers to a horizontal borehole with a radius far smaller than that of conventional drilling holes, and its borehole is formed mostly by a hydraulic jet, with a length between 10 m and 100 m and a borehole diameter between 25 mm and 50 mm [1,2,3,4]
By means of radial boreholes, we can make hydraulic fractures overcome the control of the original in-situ stress to some extent, and realize the artificial control of directional propagation toward the target zone, but because the guiding strength of a single radial drilling is limited, it is possible that the hydraulic fracture does not propagate along the orientation of the radial borehole, and instead, a deflection occurs midway, which results in an unsatisfactory stimulation effect
The results show that with a smaller radial borehole azimuth (15◦ ) and smaller horizontal in-situ stress difference (3 MPa), the single radial borehole has a significant influence on the propagation of fractures, and creates strong guidance for the directional propagation of hydraulic fractures
Summary
The term radial borehole ( known as radial well) refers to a horizontal borehole with a radius far smaller than that of conventional drilling holes, and its borehole is formed mostly by a hydraulic jet, with a length between 10 m and 100 m and a borehole diameter between 25 mm and 50 mm [1,2,3,4]. The reservoir simulation technology of radial boreholes combined with hydraulic fracturing is an innovative technology to effectively develop low-permeability, thin-layer, fractured reservoirs, water-flooded ‘dead oil areas’ and lithologic trap reservoirs [5,6]. Due to the lack of any relevant theory, the technological parameters of hydraulic fracturing guided by the single radial well are usually difficult to design scientifically, so the success rate is low and the application of this technology is greatly limited
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