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Boreholes
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Diguang Gong – 1st expert on this subject based on the ideXlab platform

study on initiation mechanisms of hydraulic fracture guided by vertical multi radial Boreholes
Rock Mechanics and Rock Engineering, 2017CoAuthors: Zhanqing Qu, Diguang GongAbstract:The conventional hydraulic fracturing fails in the target oil development zone (remaining oil or gas, closed reservoir, etc.) which is not located in the azimuth of maximum horizontal in situ stress of available wellbores. The technology of directional propagation of hydraulic fracture guided by vertical multiradial Boreholes is innovatively developed. The effects of in situ stress, wellbore internal pressure and fracturing fluid percolation effect on geostress field distribution are taken into account, a mechanical model of two radial Boreholes (basic research unit) is established, and the distribution and change rule of the maximum principal stress on the various parameters have been studied. The results show that as the radial borehole azimuth increases, the preferential rock tensile fracturing in the axial plane of radial Boreholes becomes increasingly difficult. When the radial borehole azimuth increases to a certain extent, the maximum principal stress no longer appears in the azimuth of the radial Boreholes, but will go to other orientations outside the axial plane of radial Boreholes and the maximum horizontal stress orientation. Therefore, by reducing the ratio between the distance of the radial Boreholes and increasing the diameter of the radial Boreholes can enhance the guiding strength. In the axial plane of the radical Boreholes, particularly in the radial hole wall, position closer to the radial Boreholes is more prone to rock tensile destruction. Even in the case of large radial borehole azimuth, rock still preferentially ruptures in this position. The more the position is perpendicularly far from the axis of the wellbore, the lesser it will be affected by wellbore, and the lesser the tensile stress of each point. Meanwhile, at a certain depth, due to the decrease in the impact of the wellbore and the impact of the two radial Boreholes increases accordingly, at the further position from the wellbore axis, the tensile fracture is the most prone to occur and it will be closer to the axial plane of the two radial Boreholes. The study provides theoretical support for the technology of directional propagation of hydraulic fracture promoted by radial borehole, which is helpful for planning wellcompletion parameters in technology of hydraulic fracturing promoted by radial borehole.

numerical simulation of directional propagation of hydraulic fracture guided by vertical multi radial Boreholes
Journal of Natural Gas Science and Engineering, 2016CoAuthors: Zhanqing Qu, Diguang GongAbstract:Abstract The conventional hydraulic fracturing is not effective in the target oil development zone (remaining oil or gas, trap reservoir, etc.) with available wellbores located in the azimuth of nonmaximum horizontal insitu stress. The technology of directional propagation of hydraulic fracture guided by vertical multiradial Boreholes was innovatively developed. In order to verify the technology, a 3D extended finite element numerical model of hydraulic fracturing promoted by vertical multiradial Boreholes was established using Abaqus Software, and the influence of horizontal insitu stress differences, azimuth, diameters, spacing, and lengths of radial Boreholes, rates and viscosities of fracturing fluids, Young modulus and Poisson’s ratio of rock, and reservoir permeability on propagation of hydraulic fracture guided by radial borehole row were comprehensively analyzed. Moreover, the term ‘Guidance factor (G)’ was introduced for the first time to effectively quantify guidance of radial borehole row. Finally, the guidance of the above ten factors is comprehensively evaluated through gray correlation analysis. The results showed that the directional propagation of hydraulic fracture is realized through scientifically arranged vertical radial borehole row, and ‘G’ reflects the real guidance strength of radial borehole row to hydraulic fracture. The azimuth of radial borehole row increases by 75°, G increases by 18 times. Horizontal insitu stress difference increases by 9 MPa, G increases by 95%. The borehole diameter increases by 4 cm, G decreases by 54%. The borehole spacing increases by 0.5 m, G increases by 18%. The borehole length increases by 10 m, G decreases by 40%. Young’s modulus of reservoir rock increases by 20 GPa, G decreases by 23%. Poisson’s ratio increases by 0.1, G increases by 57%. Permeability of reservoir increases by 100 times, G increases by 3.3 times. Injection rate increases by 9 m3/min, G decreases by 63%. Both excessively high and low viscosities are adverse to guidance of radial borehole to hydraulic fracture, and 50 mPa s fracturing fluid creates best guidance to propagation of hydraulic fracture. The gray correlation analysis showed that the influences (from strong to weak) of the above factors on guidance of radial borehole were listed as follows: azimuth of radial borehole > injection rate of fracturing fluid > horizontal insitu stress differences > Young’s modulus of rock > viscosity of fracturing fluid > borehole diameter of radial borehole > radial borehole spacing > reservoir permeability > length of radial borehole > Poisson’s ratio. This study provided theoretical evidence for directional propagation of hydraulic fracture promoted by radial borehole, and it predicted the guidance of radial borehole to hydraulic fracture in a certain extent, which is helpful for planning wellcompletion and fracturing operation in technology of hydraulic fracturing promoted by radial borehole.
Zhanqing Qu – 2nd expert on this subject based on the ideXlab platform

Research on Fracture Initiation Mechanisms of Hydraulic Fracturing Guided by Multiradial Boreholes
Proceedings of the International Petroleum and Petrochemical Technology Conference 2019, 2019CoAuthors: Yuxin Chen, Zhanqing Qu, Jiwei WangAbstract: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 geostress, wellbore internal pressure and fracturing fluid percolation effect on geostress field distribution are taken into account, a mechanical model of multiradial Boreholes with any number, vertical depth and azimuth angle (the angle between the radial borehole and the horizontal maximum geostress) 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 geostress difference and the diameter of the radial borehole. When the horizonal geostress difference is small, the maximum principal stress increases first and then decreases with the increase of the azimuth angle; when the horizonal geostress difference is large, the maximum principal stress decreases with the increase of the azimuth angle. When multiradial 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 geostress difference is small and the radial borehole diameter is large. This study provides theoretical support for guiding fracture by multiradial 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.

study on initiation mechanisms of hydraulic fracture guided by vertical multi radial Boreholes
Rock Mechanics and Rock Engineering, 2017CoAuthors: Zhanqing Qu, Diguang GongAbstract:The conventional hydraulic fracturing fails in the target oil development zone (remaining oil or gas, closed reservoir, etc.) which is not located in the azimuth of maximum horizontal in situ stress of available wellbores. The technology of directional propagation of hydraulic fracture guided by vertical multiradial Boreholes is innovatively developed. The effects of in situ stress, wellbore internal pressure and fracturing fluid percolation effect on geostress field distribution are taken into account, a mechanical model of two radial Boreholes (basic research unit) is established, and the distribution and change rule of the maximum principal stress on the various parameters have been studied. The results show that as the radial borehole azimuth increases, the preferential rock tensile fracturing in the axial plane of radial Boreholes becomes increasingly difficult. When the radial borehole azimuth increases to a certain extent, the maximum principal stress no longer appears in the azimuth of the radial Boreholes, but will go to other orientations outside the axial plane of radial Boreholes and the maximum horizontal stress orientation. Therefore, by reducing the ratio between the distance of the radial Boreholes and increasing the diameter of the radial Boreholes can enhance the guiding strength. In the axial plane of the radical Boreholes, particularly in the radial hole wall, position closer to the radial Boreholes is more prone to rock tensile destruction. Even in the case of large radial borehole azimuth, rock still preferentially ruptures in this position. The more the position is perpendicularly far from the axis of the wellbore, the lesser it will be affected by wellbore, and the lesser the tensile stress of each point. Meanwhile, at a certain depth, due to the decrease in the impact of the wellbore and the impact of the two radial Boreholes increases accordingly, at the further position from the wellbore axis, the tensile fracture is the most prone to occur and it will be closer to the axial plane of the two radial Boreholes. The study provides theoretical support for the technology of directional propagation of hydraulic fracture promoted by radial borehole, which is helpful for planning wellcompletion parameters in technology of hydraulic fracturing promoted by radial borehole.

numerical simulation of directional propagation of hydraulic fracture guided by vertical multi radial Boreholes
Journal of Natural Gas Science and Engineering, 2016CoAuthors: Zhanqing Qu, Diguang GongAbstract:Abstract The conventional hydraulic fracturing is not effective in the target oil development zone (remaining oil or gas, trap reservoir, etc.) with available wellbores located in the azimuth of nonmaximum horizontal insitu stress. The technology of directional propagation of hydraulic fracture guided by vertical multiradial Boreholes was innovatively developed. In order to verify the technology, a 3D extended finite element numerical model of hydraulic fracturing promoted by vertical multiradial Boreholes was established using Abaqus Software, and the influence of horizontal insitu stress differences, azimuth, diameters, spacing, and lengths of radial Boreholes, rates and viscosities of fracturing fluids, Young modulus and Poisson’s ratio of rock, and reservoir permeability on propagation of hydraulic fracture guided by radial borehole row were comprehensively analyzed. Moreover, the term ‘Guidance factor (G)’ was introduced for the first time to effectively quantify guidance of radial borehole row. Finally, the guidance of the above ten factors is comprehensively evaluated through gray correlation analysis. The results showed that the directional propagation of hydraulic fracture is realized through scientifically arranged vertical radial borehole row, and ‘G’ reflects the real guidance strength of radial borehole row to hydraulic fracture. The azimuth of radial borehole row increases by 75°, G increases by 18 times. Horizontal insitu stress difference increases by 9 MPa, G increases by 95%. The borehole diameter increases by 4 cm, G decreases by 54%. The borehole spacing increases by 0.5 m, G increases by 18%. The borehole length increases by 10 m, G decreases by 40%. Young’s modulus of reservoir rock increases by 20 GPa, G decreases by 23%. Poisson’s ratio increases by 0.1, G increases by 57%. Permeability of reservoir increases by 100 times, G increases by 3.3 times. Injection rate increases by 9 m3/min, G decreases by 63%. Both excessively high and low viscosities are adverse to guidance of radial borehole to hydraulic fracture, and 50 mPa s fracturing fluid creates best guidance to propagation of hydraulic fracture. The gray correlation analysis showed that the influences (from strong to weak) of the above factors on guidance of radial borehole were listed as follows: azimuth of radial borehole > injection rate of fracturing fluid > horizontal insitu stress differences > Young’s modulus of rock > viscosity of fracturing fluid > borehole diameter of radial borehole > radial borehole spacing > reservoir permeability > length of radial borehole > Poisson’s ratio. This study provided theoretical evidence for directional propagation of hydraulic fracture promoted by radial borehole, and it predicted the guidance of radial borehole to hydraulic fracture in a certain extent, which is helpful for planning wellcompletion and fracturing operation in technology of hydraulic fracturing promoted by radial borehole.
Zhaohong Fang – 3rd expert on this subject based on the ideXlab platform

heat transfer analysis of ground heat exchangers with inclined Boreholes
Applied Thermal Engineering, 2006CoAuthors: Hongxing Yang, Zhaohong FangAbstract:Consisting of closedloop of pipes buried in Boreholes, ground heat exchangers (GHEs) are devised for extraction or injection of thermal energy from/into the ground. Evolved from the vertical borehole systems, the configuration of inclined Boreholes is considered in order to reduce the land plots required to install the GHEs in densely populated areas. A transient threedimensional heat conduction model has been established and solved analytically to describe the temperature response in the ground caused by a single inclined line source. Heat transfer in the GHEs with multiple Boreholes is then studied by superimposition of the temperature excesses resulted from individual Boreholes. On this basis, two kinds of representative temperature responses on the borehole wall are defined and discussed. The thermal interference between inclined Boreholes is compared with that between vertical ones. The analyses can provide a basic and useful tool for the design and thermal simulation of the GHEs with inclined Boreholes.

heat transfer analysis of Boreholes in vertical ground heat exchangers
International Journal of Heat and Mass Transfer, 2003CoAuthors: Heyi Zeng, Nairen Diao, Zhaohong FangAbstract:A ground heat exchanger (GHE) is devised for extraction or injection of thermal energy from/into the ground. Bearing strong impact on GHE performance, the borehole thermal resistance is defined by the thermal properties of the construction materials and the arrangement of flow channels of the GHEs. Taking the fluid axial convective heat transfer and thermal ‘‘shortcircuiting’’ among Utube legs into account, a new quasithreedimensional model for vertical GHEs is established in this paper, which provides a better understanding of the heat transfer processes in the GHEs. Analytical solutions of the fluid temperature profiles along the borehole depth have been obtained. On this basis analytical expressions of the borehole resistance have been derived for different configurations of single and double Utube Boreholes. Then, different borehole configurations and flow circuit arrangements are assessed in regard to their borehole resistance. Calculations show that the double Utubes Boreholes are superior to those of the single Utube with reduction in borehole resistance of 30–90%. And double Utubes in parallel demonstrate better performance than those in series. 2003 Elsevier Ltd. All rights reserved.