Numerical Analysis on Fracture Propagation Behavior of Radial Wellbore Cross-Layer Fracturing Based on 3D Discrete Lattice Method

ABSTRACT: Radial wellbore fracturing, as an innovative technology for guiding fracture propagation, show great potential in improving fracture height and enhancing vertical stimulation performance, especially in multi-lithologic superimposed reservoirs. To determine the cross-layer propagation behaviors of fractures by radial wellbore fracturing in sand-shale interlayered rock mass, a numerical simulation study was conducted by employing a 3D discrete lattice method. By comparing with conventional horizontal well fracturing, the characteristic of fracture initiation and propagation of radial wellbore fracturing was illuminated, and the effect of layer combination sequence and radial wellbore dimension on fracture height was analyzed. The results indicate that the fracture has more significant cross-layer ability in radial wellbore fracturing, as compared to horizontal well fracturing, which could inhibit the fluid leakage between lithologic interfaces and increase the average fracture height by 75%. There is a positive correlation between fracture height and radial borehole length. Greater radial borehole length benefits increasing fracture height and activating more target shale layers, shifting the fracture morphology from arresting pattern to cross-layer pattern and skip-layer pattern. Regards to the lithologic layer sequence, setting the root end of radial borehole in high-strength sandstone layer is more conducive to achieving cross-layer propagation and improving fracture height, instead of setting in low-strength shale layer. These findings are expected to offer new insights and theoretical foundations for enhancing interlayered connectivity and stimulated reservoir volume in multi-layered formations. 1. INTRODUCTION Horizontal wellbore fracturing technology is widely used in unconventional hydrocarbon resources production to improve oil-gas flow and reservoir permeability (Chen al., 2019; Hu al., 2020; Lin al., 2018). However, these reservoirs, such as shale oil, coalbed methane, tight oil, etc., generally develop high strength and high dense barrier-layer structures (Cheng al., 2012; Fu al., 2023). This limits the longitudinal extension of hydraulic fracture (HF), which is not conducive to the activation of lateral layers, and reduces the volume reconstruction range of the reservoir. Increasing the HF height is the key to promote the development of multi-lithologic superimposed reservoir (Wu al., 2024; Zhang al., 2023).