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

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.

A Dynamic Propagation Numerical Model of Hydraulic Fracture Interactions with Pre-Existing Complex Natural Fractures

“…Deng et al [13] studied the influence of the original rock stress on the fracture behavior of a single fracture based on the stress intensity factor criterion, but did not consider the influence of the presence of natural fractures on fracture initiation and expansion. Zhang et al [14] analyzed the influence of displacement and stress difference on hydraulic fracturing fracture propagation by carrying out largescale true triaxial tests on shale outbursts containing natural fractures. Hou et al [15] carried out true triaxial hydraulic fracturing material model experiments on tight limestone outcroppings, and analyzed the influence of in situ stress difference, fracturing fluid viscosity, variable displacement, acid treatment and other factors on fracture propagation law.…”

The Mechanical Properties and Fracture Characteristics of Shale Layered Samples from the Lucaogou Formation Considering Natural Crack and Mineral Distribution

“…This brings great difficulty to simulation of the reservoir. Therefore, it is fairly important to understand the mechanical and fracture properties of different layers, which is the key to optimizing a hydraulic fracturing strategy [7,8].…”

“…Li et al [6] analyzed the crack height and its ability to penetrate bedding under the influence of layer thickness and lithology based on a triaxial hydraulic fracturing simulation. Zhang et al [8] found that the bedding direction of a Lucaogou rock has a significant effect on its tensile strength and brittleness. Zou et al [11] believed that the difference in rock mechanics between layers cannot effectively inhibit the growth of fracture height but has a significant effect on the fracture width.…”

Investigation on the influence factors for the fracturing effect in fractured tight reservoirs using the numerical simulation

“…Many scholars have studied the effects of natural fractures on the propagation pattern and fracture morphology of hydraulic fractures mainly by means of experiments and numerical simulations. Zhou et al 5,6 Cheng et al 7 and Zhang et al 8 studied the effects of main stress difference and natural fractures on the fracture morphology of horizontal wells by means of true triaxial hydraulic fracture experiments and acoustic emission monitoring, respectively. However, these studies did not elaborate the relationship and sensitivity between the influencing factors.…”