Influence of Vertical Density and Phase Angle on Fracture Initiation and Propagation Behavior in Multi-Branch Radial Borehole Fracturing

ABSTRACT: Multi-branch radial borehole fracturing, as a novel stimulation method, shows great potential in guiding directional propagation of multiple fractures towards the sweet spots of oil and gas reservoir. However, the competitive initiation behavior of hydraulic fractures from multiple radial boreholes are not fully understood. To describe non-uniform propagation and spatial evolution of fractures, this paper proposed a three-dimensional fully-coupled model of multi-branch radial borehole fracturing by using discrete lattice method. The effects of vertical density and phase angle on fracture initiation and propagation behavior were analyzed. The results indicate that with the increase in the vertical density of radial boreholes, the breakdown pressure decreases. It is recommended to use a vertical density of at least 3 boreholes/m to enhances directional propagation area and improves fracture connectivity. Phase angles have a significant effect on the fracture initiation efficiency. Under spiral multi-branch radial borehole model, it is advisable to adopt vertical phase angles of 0°, 90°, and 120° to maximize the utilization of radial boreholes. Under the planar-oriented multi-branch radial borehole model, the number of radial boreholes within the same horizontal plane should not exceed 3. The findings of this work are expected to provide valuable insights for radial borehole fracturing design. 1. INTRODUCTION Radial borehole fracturing is an innovative technique that combines horizontal radial borehole with hydraulic fracturing (Liu et al., 2018; Guo et al., 2022). This method has been successfully tested and applied in many oil and gas fields worldwide, leading to notable increases in production (Novokreshchennykh and Raspopov., 2016; Chen and Zhan., 2017; Yang et al., 2022). Typically, radial boreholes are drilled by high-pressure water jets technology with diameters between 20 mm and 50 mm (Guo et al., 2022). Compared to traditional hydraulic fracturing, radial borehole is favorable to guide the directional propagation of hydraulic fractures towards the sweet spots of oil and gas reservoirs. Additionally, radial boreholes offer a more economical alternative to horizontal wells. However, due to the inherent heterogeneity of geological formations, the stress reconstruction of a single radial borehole is insufficient to effectively guide the directional propagation of fractures. This may result in fractures deviating from their intended path, leading to less than optimal improvements in production, thereby limiting the broader application of this technology (Li, 2018). To address these challenges, a new approach has been proposed to guide fracture propagation directionally using multi-branch radial boreholes (Guo et al., 2016).