Effect of layer orientation on acoustic emission characteristics of anisotropic shale in Brazilian tests

Wang, Jun; Xie, Lingzhi; Xie, Heping; Ren, Li; He, Bo; Li, Cunbao; Yang, Zhipeng; Gao, Chao

doi:10.1016/j.jngse.2016.03.046

Cited by 114 publications

(28 citation statements)

References 22 publications

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“…The heterogeneity of the specimens is due to sedimentation and diagenesis processes as evidenced by the presence of bioturbation, possible ripple marks, and soft sediment deformation [ Grigg , ]. In addition to the experimental results of this study, the tendency of fracture patterns due to anisotropic feature (e.g., layered system) can also be found from the reference [e.g., Simpson , ; Mighani et al ., ; Wang et al ., ; Mighani et al ., ]. The impact of flaws as well as layer orientations on the direction of crack propagation will be investigated in the numerical simulation.…”

Section: Resultsmentioning

confidence: 99%

“…Despite the debate the Brazilian test coupled with a digital imaging and acoustic emission measurement is very useful for analyzing the influence of material heterogeneity on crack initiation and propagation [e.g., Simpson , ; Mighani et al ., ; Wang et al ., ; Mighani et al ., ]. Furthermore, recent experiments have been performed to account for the effect of the anisotropy or layered system of rocks on tensile strength and crack patterns [e.g., Tavallali and Vervoort , , ; Dan et al ., ; Vervoort et al ., ].…”

Section: Introductionmentioning

confidence: 99%

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Effects of spatial heterogeneity and material anisotropy on the fracture pattern and macroscopic effective toughness of Mancos Shale in Brazilian tests

Sun

Ingraham

et al. 2017

JGR Solid Earth

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For assessing energy‐related activities in the subsurface, it is important to investigate the impact of the spatial variability and anisotropy on the geomechanical behavior of shale. The Brazilian test, an indirect tensile‐splitting method, is performed in this work, and the evolution of strain field is obtained using digital image correlation. Experimental results show the significant impact of local heterogeneity and lamination on the crack pattern characteristics. For numerical simulations, a phase field method is used to simulate the brittle fracture behavior under various Brazilian test conditions. In this study, shale is assumed to consist of two constituents including the stiff and soft layers to which the same toughness but different elastic moduli are assigned. Microstructural heterogeneity is simplified to represent mesoscale (e.g., millimeter scale) features such as layer orientation, thickness, volume fraction, and defects. The effect of these structural attributes on the onset, propagation, and coalescence of cracks is explored. The simulation results show that spatial heterogeneity and material anisotropy highly affect crack patterns and effective fracture toughness, and the elastic contrast of two constituents significantly alters the effective toughness. However, the complex crack patterns observed in the experiments cannot completely be accounted for by either an isotropic or transversely isotropic effective medium approach. This implies that cracks developed in the layered system may coalesce in complicated ways depending on the local heterogeneity, and the interaction mechanisms between the cracks using two‐constituent systems may explain the wide range of effective toughness of shale reported in the literature.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of spatial heterogeneity and material anisotropy on the fracture pattern and macroscopic effective toughness of Mancos Shale in Brazilian tests

Sun

Ingraham

et al. 2017

JGR Solid Earth

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“…Under different sedimentary environment conditions, the bedding density of shale formation has a great difference. erefore, the bedding plays a significant role in both mechanical behavior and engineering activities [1]. During long horizontal-section drilling and hydraulic fracturing construction engineering, the surrounding rock is subjected to loading and unloading states.…”

Section: Introductionmentioning

confidence: 99%

Effects of Cyclic Loading on the Mechanical Properties of Mature Bedding Shale

Guo

Yang

Wang

et al. 2018

Advances in Civil Engineering

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We investigated the mechanical properties of mature bedding shale under cyclic loading conditions, with an application to the design of hydraulic fracturing in shale gas wells. Laboratory experiments were conducted on shale samples under two principal loading orientations. Testing results showed that accumulated fatigue damage occurs in a three-stage process. Analysis of fatigue damage at different maximum stress levels shows that fatigue life increases as a power-law function with maximum stress decreasing. And the maximum stress significantly affects the fatigue life. Further, the elastic part of shale rock deformation was recovered in the unloading process, whereas the irreversible deformation remained. e irreversible deformation, growth trend, and accumulation of the total fatigue were directly related to the fatigue damage. is process can be divided into 3 stages: an initial damage stage, a constant velocity damage stage, and an accelerated damage stage, which accounted for about one-third of the fatigue damage. Shale rock is a nonhomogeneous material, and the bedding is well developed. Its fatigue life differs greatly in two principal loading orientations, even under the same loading conditions. All of these drawn conclusions are of great importance for design of hydraulic fracturing in shale gas wells.

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“…Tests conducted on Brazilian disks specimens which are traditionally used to indirectly calculate rock's tensile strength prove significant influence of laminations inclination on the mechanical response of the materials (Wang et al 2016;Mokhtari and Tutuncu 2016;Mousavi Nezhad et al 2018). Zhong et al (2015) also studied the effect of damage at microscale on the overall macroscopic response of the shale samples subjected to triaxial compression and highlighted that both bedding inclinations and different confining pressures influence on the compressive strength, elastic modulus, crack morphology and opening modes.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study and Numerical Modeling of Fracture Propagation in Shale Rocks During Brazilian Disk Test

et al. 2018

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Reliable prediction of fracture process in shale-gas rocks remains one of the most significant challenges for establishing sustained economic oil and gas production. This paper presents a modeling framework for simulation of crack propagation in heterogeneous shale rocks. The framework is on the basis of a variational approach, consistent with Griffith's theory. The modeling framework is used to reproduce the fracture propagation process in shale rock samples under standard Brazilian disk test conditions. Data collected from the experiments are employed to determine the testing specimens' tensile strength and fracture toughness. To incorporate the effects of shale formation heterogeneity in the simulation of crack paths, fracture properties of the specimens are defined as spatially random fields. A computational strategy on the basis of stochastic finite element theory is developed that allows to incorporate the effects of heterogeneity of shale rocks on the fracture evolution. A parametric study has been carried out to better understand how anisotropy and heterogeneity of the mechanical properties affect both direction of cracks and rock strength.

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Effect of layer orientation on acoustic emission characteristics of anisotropic shale in Brazilian tests

Cited by 114 publications

References 22 publications

Effects of spatial heterogeneity and material anisotropy on the fracture pattern and macroscopic effective toughness of Mancos Shale in Brazilian tests

Effects of spatial heterogeneity and material anisotropy on the fracture pattern and macroscopic effective toughness of Mancos Shale in Brazilian tests

Effects of Cyclic Loading on the Mechanical Properties of Mature Bedding Shale

Experimental Study and Numerical Modeling of Fracture Propagation in Shale Rocks During Brazilian Disk Test

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