Effect of Interlaminar Difference on Height Propagation Behavior of Hydraulic Fracture in Lucaogou Shale

Abstract

ABSTRACT: The shale oil reservoir of Lucaogou Formation is characterized by complex lithology changes in vertical direction and lamination. To simulate the lithology variation of shale oil formation, downhole cores with different lithologies were prepared and bonded to layered samples. After that, the influence of interlaminar difference on propagation behavior of hydraulic fractures (HFs) was investigated through laboratory hydraulic fracturing and mechanical characteristics analysis. The result shows that mechanically weak bedding planes (BPs) leads to obvious anisotropy of rock mechanical properties. The rock samples is unstable when loaded along the parallel BPs direction, the tensile strength decline significantly, which is about 20% of the tensile strength measured perpendicular to BPs. The brittleness of rock samples measured parallel to BPs is greater than that measured perpendicular to BPs, by about two times. This results in HFs induced by low-viscosity slickwater are easily arrested by BPs, can not penetrate interlayer. HFs induced by high viscosity gel can penetrate the bonding interface. The difference of tensile strength between layers increases, the decrease degree of fracture width increases 2.5 times. This will impede proppant placement in interlayer. This research results provide a basis for the optimization of hydraulic fracturing of Lucaogou shale oil reservoir. 1. INTRODUCTION The reservoirs of Lucaogou Formation in Jimusar sag, Junggar Basin are saline lacustrine and delta facies (Zou et al., 2020; Nie et al., 2011). The variation of climate and source supply intensity as well as the periodical fluctuation of lake level lead to the longitudinal lithology variation, and BPs development (Li et al., 2020; Zhang et al., 2021; Yang et al., 2018; Zhi et al., 2019 ). The influence of interlayer difference and BPs on reservoir fracture propagation is unclear. The selection of fracturing techniques and engineering parameters lacks theoretical support, and HFs height and vertical fracturing volume are limited (Lei et al., 2021; Jiang et al., 2021;). Understanding the influence of interlayer difference and BP structure on fracture propagation is the key to optimize hydraulic fracturing strategy, which is of great significance to improve the adaptability of fracturing process parameters and realize the overall utilization of multi-layer sweet spot body.