Vertical propagation behavior of hydraulic fracture guided by radial borehole: Insight for horizontal well stimulation in multilayered reservoirs

Abstract

The strong vertical discontinuities pose a fundamental challenge to optimizing stimulated reservoir volume (SRV) in multilayered reservoirs. This research proposes a radial borehole-assisted horizontal well fracturing technology, which is expected to achieve effective vertical stimulation and commingled production across multiple pay zones. Under different geological and engineering conditions, the vertical propagation behavior of hydraulic fractures guided by radial boreholes can be determined by adjusting the interlayered lithologies and radial borehole configurations in experimental samples. Experimental results reveal four fracture network patterns: passivated, cross-layer, skip-layer, and hybrid fractures in the radial borehole fracturing. The radial boreholes perform better fracture guiding performances in the high-brittleness interlayers, which form cross-layer and hybrid fracture networks to improve the growth height. Hydraulic fractures tend to propagate from high-strength to low-strength layers under radial borehole guidance. When radial boreholes interconnect multiple lithology layers, hydraulic fractures initiate preferentially in lower-strength zones rather than remaining confined to borehole root ends. Increased radial borehole length and diameter facilitate fracture skip-layer initiation and cross-layer propagation, while multiple borehole branches enhance fracture penetration across high-strength interlayers. Radial boreholes with inclination angles below 30° enhance fracture height by generating cross-layer and hybrid fracture networks. Furthermore, an inter-borehole phase angle of less than 180° facilitates single-wing fracture cross-layer propagation. Fracture height is primarily governed by radial borehole length, followed by quantity, inclination angle, and diameter. Based on the geometric similarity criteria, the recommended parameters for radial borehole-assisted fracturing in a 5½-inch horizontal well include a length > 15 m, an inclination angle < 30°, and a diameter > 52 mm to ensure effective stimulation across three or more pay zones. Finally, the field-scale numerical model was developed to simulate the optimized radial borehole fracturing and demonstrate the technical superiority. These findings are expected to provide an in-depth understanding of the effective stimulation in multilayered reservoirs.

Keywords

Multilayered reservoirs / Radial borehole fracturing / Interlayered lithologies / Radial borehole configurations / Field-scale numerical model

CRediT authorship contribution statement

Tengda Long: Writing – original draft, Methodology, Investigation. Gensheng Li: Methodology, Funding acquisition. Xiaoguang Wu: Funding acquisition. Zhongwei Huang: Funding acquisition. Zixiao Xie: Writing – review & editing. Rui Yang: Investigation. Xianzhi Song: Resources. Shouceng Tian: Methodology. Haizhu Wang: Resources. Naikun Hu: Investigation. Xiaohua Wang: Software. Xiangyang Wang: Writing – review & editing. Xiaoxuan Li: Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by the National Natural Science Foundation of China (Nos. U24B6001, 52421002, 52474016, and 52020105001), Research on Key Technologies for Exploration and Development of Dry Geothermal Resources (No. 2022DJ5503), and Deep-land National Science and Technology Major Project of China (No. 2024ZD1003504).

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