Acoustic and fractal analyses of the mechanical properties and fracture modes of bedding‐containing shale under different seepage pressures

Wu, Zhonghu; Lou, Yili; Yin, Shuai; Wang, Anli; Líu, Hao; Sun, Wenjibin; Zuo, Yujun; Chen, Bin

doi:10.1002/ese3.772

Cited by 22 publications

(9 citation statements)

References 47 publications

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“…β denotes the average of the parameters of the physical properties of the primitive, m indicates the nature parameter of the distribution function, whose physical meaning reflects the homogeneity of the material medium, defined as the homogeneity coefficient of the material medium, reflecting the degree of homogeneity of the material, f(x) is the density of the statistical distribution of the physical properties x of the material (rock) primitive. The material parameters in this test are derived from the mechanical parameters of shale in the Lower Cambrian Niutitang Formation in north area of Guizhou (Wu et al, 2020), and are summarized in Table 1, where the values in brackets represent the uniformity coefficient of this parameter. The elastic modulus diagram after the assignment is shown in Figure 5D.…”

Section: Shale 3d Model Reconstructionmentioning

confidence: 99%

Three-dimensional numerical simulation study of pre-cracked shale based on CT technology

Wu²,

Zuo³

et al. 2023

Front. Earth Sci.

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Due to the heterogeneity of rock media, it is difficult to truly reflect its internal three-dimensional microstructure in physical tests or numerical simulation. In this study, CT scanning technology and numerical image processing technology are used, and the finite element software RFPA-3D is used to establish a three-dimensional non-uniform numerical model that can reflect the meso structure of rock mass. In order to study the fracture mechanism of shale with prefabricated fractures, seven groups of three-dimensional numerical models with prefabricated fractures from different angles were constructed, and Brazilian fracturing numerical simulation tests were carried out. The results show that method of reconstructing 3D numerical models by CT scanning is feasible and provides a viable method for in-depth study of the micromechanics of shale. Prefabricated fractures and quartz minerals have significant effects on the tensile strength of shale, and both will weaken the destructive strength of shale specimens. The damage modes of Brazilian disc specimens containing prefabricated fissures can be divided into four categories. The damage process is divided into budding, plateauing and surge periods by acoustic emission. The crack initiation angle of the prefabricated fissure tip increases with increasing fissure angle, and the MTS criterion can be used as a basis for judging prefabricated fissure initiation. The results of the study are important guidance for the fracture initiation mechanism and fracture expansion law of the fractured layer containing natural fractures in the hydraulic fracturing process.

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Section: Shale 3d Model Reconstructionmentioning

confidence: 99%

Three-dimensional numerical simulation study of pre-cracked shale based on CT technology

Wu²,

Zuo³

et al. 2023

Front. Earth Sci.

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“…In Eq. 1, the mechanical property parameters of the unit are characterized by α, such as the modulus of elasticity and compressive strength, where α0 characterizes the average value of the mechanical property parameters for the unit and m Frontiers in Earth Science frontiersin.org characterizes the homogeneity of the material; the more homogeneous the material, the larger the m. According to the literature (Zhu et al, 2011;Lou et al, 2020;Wu et al, 2020), each known mechanical parameter for the shale is shown in Table 1. In order to study the mechanical properties, rupture process and acoustic emission signal evolution characteristics of shale containing different inclination angles of natural cracks at microscopic scale, so as to establish numerical models of shale specimens with internal natural crack inclination angles of 0 °, 15 °, 30 °, 45 °, 60 °, 75 °, 90 °and control group without natural cracks under uniaxial compression conditions, a total of 8 groups, were tested numerically by RFPA2D-DIP, and the mechanical loading model is shown in Figure 7, loaded by displacement control volume.…”

Section: Numerical Modelmentioning

confidence: 99%

Study on the influence of natural cracks on the mechanical properties and fracture mode for shale at the microscale: An example from the Lower Cambrian Niutitang Formation in northern Guizhou

Yanɡ

Wu²,

Wang³

et al. 2023

Front. Earth Sci.

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A large number of natural cracks exist in shale reservoirs, and the presence of natural cracks weakens the integrity of shale, which is an important factor governing the effectiveness of shale gas extraction. In this paper, shales from the Lower Cambrian Niutitang Formation in northern Guizhou were scanned by electron microscopy, their microstructures were selected for digital image processing, and uniaxial compression numerical tests were conducted on shale models containing different natural crack dips using the rock fracture process system RFPA2D-DIP to study the effects of natural cracks on the mechanical properties and fracture patterns of shales at the microscopic scale. The study shows that the peak strength and elastic modulus of shale increase with increasing natural crack inclination angle. The fracture modes of shale at the microscopic scale can be roughly divided into four categories: similar to I-type fractures (0°), oblique I-type fractures (15°, 45°, 60°, 75°), folded line fractures (30°), and V-type fractures (90°). Natural cracks within shale are found to have a significant effect on the distribution of stress. Acoustic emission can reflect the stress change and rupture process for shales containing natural cracks with different dip angles at the microscopic scale. The presence of natural cracks has a significant effect on the AE energy and fractal dimension. The magnitude of the AE energy increases with increasing stress level and reaches a maximum value at 90°, while the value of the fractal dimension is found to zigzag upwards because the value of the fractal dimension is jointly influenced by both newborn cracks and native natural cracks.

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“…Figure 8 is a numerical model obtained by converting an image after digital image processing. The material parameters of the micromedia in the shale are shown in Table 1 [39].…”

Section: Establishment Of the Numerical Modelmentioning

confidence: 99%

Study on the Microscale Tensile Properties of Lower Cambrian Niutitang Formation Shale Based on Digital Images

Song

Wang³

et al. 2020

Geofluids

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Tensile strength is an important parameter that affects the initiation and propagation of shale reservoir fractures during hydraulic fracturing. Shale is often filled with minerals such as calcite. To explore the effect of calcite minerals on the tensile strength and failure mode of shale, in this paper, lower Cambrian shale cores were observed by microslice observations and core X-ray whole-rock mineral diffraction analysis, and 7 groups of numerical direct tensile tests were performed on simulated shale samples with different azimuth angles. The test results show that as the azimuth angle α increases, the tensile strength of the samples gradually decreases, and the fracture rate also shows a decreasing trend. The failure modes can be summarized as root-shaped (0° and 15°), step-shaped (30 and 45°), fishbone-shaped (60°), and river-shaped (75° and 90°) fracturing. The smaller the azimuth angle α, the easier it is for hydraulic fractures to propagate along the direction of the calcite veins and inhibit the formation of fracture networks in the shale matrix. Considering the correlation between the acoustic emission characteristics and failure mode, the fractal dimension is used to reflect the microscopic failure mode of shale. The larger the fractal dimension, the higher the fracture rate is, the more microcracks exist at the edge of the main crack, the more severe the internal damage is, and the more complex the failure mode of the sample is. As the azimuth angle α increases, the fractal dimension shows a decreasing trend, and the crack becomes smoother. This research has important reference value for the study of hydraulic fracture initiation mechanisms and natural fracture propagation.

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Acoustic and fractal analyses of the mechanical properties and fracture modes of bedding‐containing shale under different seepage pressures

Abstract: This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Cited by 22 publications

References 47 publications

Three-dimensional numerical simulation study of pre-cracked shale based on CT technology

Three-dimensional numerical simulation study of pre-cracked shale based on CT technology

Study on the influence of natural cracks on the mechanical properties and fracture mode for shale at the microscale: An example from the Lower Cambrian Niutitang Formation in northern Guizhou

Study on the Microscale Tensile Properties of Lower Cambrian Niutitang Formation Shale Based on Digital Images

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