Fracture Morphology in Glutenite Reservoirs Stimulated by Radial Borehole Fracturing
Authors: Yong Yuning , Tian Shouceng , Guo Zhaoquan , Wang Tianyu , Wei Chengxiang , Zhai Jiaheng , Sheng Mao 
Published: August 2024

ABSTRACT:
Numerous oil resources have been found in glutenite reservoirs. However, multi-stage hydraulic fracturing with horizontal wells faces the challenge of insufficient stimulation due to the pronounced heterogeneity of the reservoir. Radial borehole fracturing presents a promising alternative for efficiently exploiting glutenite reservoirs. This paper experimentally investigates the characteristics of fracture morphology in glutenite reservoirs stimulated by radial borehole fracturing. The influence of radial borehole azimuths and branches is discussed. The results show that fracture morphologies of radial borehole fracturing in glutenite reservoirs are collectively affected by the in-situ stress, radial borehole, and pebbles in glutenite. Three distinct behaviors are observed when fractures encounter pebbles: fracture bypassing, penetration, and arrest. These interactions contribute to the observed non-planar characteristics of the fracture morphologies. Radial boreholes with the azimuth of 30° and 45° demonstrated the ability to guide directional fracture propagation, potentially leading to the formation of multi-branch fractures. Increasing the azimuth decreases the guiding ability of the radial borehole. Abundant different pebbles increase fracture tortuosity, which can be mitigated by perpendicularly arranging multiple radial boreholes. This research provides valuable insights into the feasibility of applying radial borehole fracturing for glutenite reservoirs and provides guidance for optimizing the fracturing design.

1. INTRODUCTION
Glutenite refers to rocks containing many pebbles with a diameter greater than 2 mm (Liu et al., 2023a). Glutenite reservoirs are one of the unconventional oil and gas resources. In recent years, abundant oil resources have been discovered in glutenite reservoirs, being important supplementary resources for hydrocarbons (Li et al., 2020; Qin et al., 2020). Glutenite reservoirs exhibit extremely low porosity and permeability, coupled with strong rock heterogeneity, resulting in significant challenges in their production (Liu et al., 2022). Multi-stage hydraulic fracturing in horizontal wells is the primary technology currently used for developing glutenite reservoirs. However, it also has difficulties such as ineffective utilization of reservoirs and a low investment-to-output ratio (Li et al., 2019). Radial borehole fracturing that combines ultra-short radius radial horizontal borehole (briefly radial borehole) with hydraulic fracturing is an emerging technique for extracting oil and gas reservoirs (Fu et al., 2015; Huang et al., 2020). This technique is carried out by drilling multiple horizontal boreholes at different depths and orientations from a central vertical well, followed by hydraulic fracturing to create multiple hydraulic fractures along the radial boreholes and pointing toward the target sweet spots of oil and gas. These interconnected fractures form a complex network, increasing the stimulation volume of the reservoir. Radial borehole fracturing has been successfully implemented in many countries (Bruni et al., 2007; Cirigliano and Talavera Blacutt, 2007; Kamel, 2016). Applying radial borehole fracturing to glutenite reservoirs is anticipated to achieve efficient development of oil and gas resources.