3D anisotropy in shear failure of a typical shale

Fan, Zidong; Ren, Li; Xie, Heping; Zhang, Ru; Li, Cun-Bao; Lu, Huijun; Zhang, Anlin; Zhou, Qin; Ling, Wei-Qiang

doi:10.1016/j.petsci.2022.10.017

Cited by 15 publications

(4 citation statements)

References 61 publications

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“…Lu et al 3 used numerical simulation to study the triaxial compression characteristics and acoustic emission evolution characteristics of the backfill-rock composite structure in view of its deformation and failure. Fan et al 4 conducted a series of shear tests on different types of stratified shales, monitored the failure process of the specimens with AE, and analyzed the shear failure mechanism of different types of stratified shales. Akdag.S et al 5 conducted a series of triaxial compression tests on the granite in view of the rockburst problem faced in the process of deep resource mining, and used a newly developed acoustic emission technology (AE) to study the post-peak energy evolution.In order to study the failure behavior of cracked rock, Liu et al…”

Section: Acoustic Emission and Fractal Characteristics Of Red Beds So...mentioning

confidence: 99%

Acoustic emission and fractal characteristics of red beds soft rock under water-force coupling

Chen,

Liu,

Jia

et al. 2023

Preprint

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Groundwater has significant influence on the mechanical properties of surrounding rock. Aiming at the large deformation of surrounding rock of red layer soft rock tunnel affected by groundwater, the uniaxial graded loading tests were carried out on red beds soft rock with different water content. The failure process of the specimen was monitored by acoustic emission (AE) and the crack evolution law was analyzed, and the scanning electron microscopy (SEM) was used to compare the microstructure of the specimens before and after immersion. Combined with fractal theory, the monofractal and multifractal characteristics of AE ringing count during the loading process of red layer soft rock were analyzed. The results show that, with the gradual increase of water content, the AE ringing count before the yield stage gradually decreased, and the corresponding cumulative ringing count at the same time gradually decreased, and the decrease was large in the early stage of immersion, and decreased in the later stage. The cumulative ringing curve gradually slowed down, the internal crack appeared earlier, the cumulative ringing curve stepped significantly, the AE signal amplitude gradually weakened, and the bandwidth of each frequency band gradually decreased. The failure of red beds soft rock with different water content is dominated by shear crack, and with the gradual increase of water content, the proportion of shear crack increases gradually, and the AE b value decreases gradually. With the gradual increase of the relative peak strength, the correlation dimension D of red beds soft rock with different water content increases first and then decreases. At 80% of the relative peak strength, the correlation dimension D reaches its maximum value and then drops sharply until it is maintained at a relatively low level, and the correlation dimension D gradually decreases with the water content. The fitting correlation coefficients of different water content (lnC(r), lnr) are all above 0.9, indicating that the AE ringing count of water-bearing red beds soft rock has fractal characteristics, and the higher the correlation coefficient, the higher the self-similarity of AE ringing count sequence. As the weight q gradually increases, the generalized fractal dimension D(q) gradually decreases. When q≠0, under the condition of the same q, D(q) presents a trend of first increasing and then decreasing. The multifractal characteristics of AE ringing count of red layer soft rock with different water content is inverted ‘U’ shape. From the natural state to immerse 1d, the ∆α gradually increases, and from 1d to 7d, the ∆α gradually decreases. When saturation is not reached, ∆f < 0 indicates that the number of cracks in the specimen is small, when saturation is reached, ∆f > 0 indicates that a large number of cracks are generated inside the specimen and macro cracks are formed. This research can provide a reliable theoretical basis for the construction and maintenance of large deformation of water-rich soft rock tunnel excavation, and have certain engineering significance.

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Section: Acoustic Emission and Fractal Characteristics Of Red Beds So...mentioning

confidence: 99%

Acoustic emission and fractal characteristics of red beds soft rock under water-force coupling

Chen,

Liu,

Jia

et al. 2023

Preprint

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“…It is of great engineering significance to study the mechanical response behavior and macro- and microfailure characteristics of shale samples under dynamic pulse load. In the study of mechanical response behavior, acoustic emission (AE) technology is very effective in rock microcrack location, and digital image correlation (DIC) technology can record displacement fields on deformed solid surfaces with high resolution, so both methods are used to continuously collect real-time damage evolution data during testing . AE signals were employed to assess changes in crack damage zones and failure features of Indian Gondwana shale, which suggested that the orientation of the bedding planes and the extent of heat treatment primarily regulated the intensity of fracturing as detected by acoustic signals .…”

Section: Introductionmentioning

confidence: 99%

“…In the study of mechanical response behavior, acoustic emission (AE) technology is very effective in rock microcrack location, and digital image correlation (DIC) technology can record displacement fields on deformed solid surfaces with high resolution, so both methods are used to continuously collect real-time damage evolution data during testing. 28 AE signals were employed to assess changes in crack damage zones and failure features of Indian Gondwana shale, which suggested that the orientation of the bedding planes and the extent of heat treatment primarily regulated the intensity of fracturing as detected by acoustic signals. 29 Li et al 30 evaluated rock damage from the perspective of AE energy and established a constitutive model of AE energy parameters representing damage variables.…”

Section: Introductionmentioning

confidence: 99%

Damage Evolution and Splitting Failure Mechanism of Layered Rock under Dynamic Pulse Load

Wei,

Yang,

Zhai

et al. 2024

Energy Fuels

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In order to study the damage evolution and splitting failure characteristics of shale with different bedding orientations under dynamic pulse load, different impact velocities (40, 50, 60, 70 m/s) are selected to carry out dynamic pulse load on D-type and S-type shale samples. Ultrasonic testing, Brazilian splitting test [combined with digital image correlation technology and acoustic emission (AE) monitoring], and nuclear magnetic resonance are carried out on shale samples before and after impact. The results show that the P-wave velocity damage coefficient and splitting mechanic parameters of D-type shale show exponential attenuation, while those of S-type shale show linear attenuation. With the increase of impact velocity, the time-domain spectra of D-type and S-type shale show different degrees of waveform distortion. The frequency-domain spectra present a change characteristic of "high-frequency decrease, low-frequency increase", the total energy of energy spectra decreases, and the main frequency band shifts from medium frequency sub-band (fourth to sixth) to low frequency sub-band (especially first). The AE characteristics of D-type shale are peak distribution with obvious brittle fracture characteristics, while S-type shale is uniformly distributed with progressive failure characteristics. The horizontal strain cloud map shows a band-like stress concentration distribution. Before and after impact, the total porosity of D-type shale decreases, while that of S-type shale increases. The fractal dimension of mesopores generally increases, while the fractal dimension of macropores remained basically unchanged. The existence of the bedding surface is the main reason for the difference in fracture mechanism of different types of shale, and the weakening of the bedding surface caused by impact load is an important factor that complicates the complexity of this difference.

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“…However, shale, as one of the most widespread sedimentary formations on Earth, exposed well-defined anisotropy in the form of bedding, lamination, foliation (repetitive layering), fissuring, or jointing. , The fissures or joints could generate anisotropic and preferential fluid flow paths , and lead to a certain level of discontinuity, depending on the size of the problem of interest . For example, for a regional problem on the reservoir scale, the associated deformation discontinuity across enormous fissures and joints could be ignored, while they mostly contribute to the fluid flow through the so-called multiple porosity model. ,– Therefore, in this study, we focus on the so-called intact anisotropy, which means that for any material point in the domain, the stiffness and/or permeability vary with the observing direction. ,, This anisotropy can have a significant impact on the way that fractures propagate through the rock, , the direction in which gas flows, , and the shear failure. – Therefore, coupled hydro-mechanical simulations should take the anisotropic characteristics into account. ,– …”

Section: Introductionmentioning

confidence: 99%

Material Constants of Anisotropic Poroelasticity and Its Impacts on Shale Gas Production

Zhang,

Yin,

Yan

2023

Energy Fuels

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While the production of shale gas is always accompanied by stratum deformation, previous studies have commonly assumed isotropy to simplify the modeling process despite substantial experimental evidence supporting the anisotropy of these formations. This work contributes to both theoretical and practical aspects of anisotropy. For the theoretical aspect, a novel mixture theory approach is used to explore the poromechanical constants of anisotropic poroelasticity. By incorporating new elements in the modeling of intrinsic solid density and unjacketed frame deformation, we are able to establish a complete set of parameters considering micro-inhomogeneity and micro-anisotropy in a macroscopically anisotropic porous medium like shale. The bounds on the material constants are established, and their relationship with the intrinsic material constants of poroelasticity proposed by Cheng ( 2021) is discussed. In a practical context, we examine the impacts of anisotropy in a 3D shale gas reservoir considering both elastic and permeability anisotropy. For elastic anisotropy, compared with the isotropic counterpart, we identify significant dissimilarities in the horizontal stress parallel to the wellbore (σ xx here) between assumptions of isotropy and transverse isotropy. For permeability anisotropy with an inclined plane of isotropy, the gas production is largely inhibited, and we could observe the stress distribution reorientation. To conclude, isotropic models are unable to reproduce the stress changes predicted by the anisotropic models, and this research contributes to a better understanding of anisotropy in shale gas reservoirs.

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3D anisotropy in shear failure of a typical shale

Cited by 15 publications

References 61 publications

Acoustic emission and fractal characteristics of red beds soft rock under water-force coupling

Acoustic emission and fractal characteristics of red beds soft rock under water-force coupling

Damage Evolution and Splitting Failure Mechanism of Layered Rock under Dynamic Pulse Load

Material Constants of Anisotropic Poroelasticity and Its Impacts on Shale Gas Production

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