Grain-scale analysis of fracture paths from high-cycle hydraulic fatigue experiments in granites and sandstone

Zhuang, Łi; Zang, Arno; Jung, Sung Gyu

doi:10.1016/j.ijrmms.2022.105177

Cited by 14 publications

(5 citation statements)

References 51 publications

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“…The intact rock has a very low permeability of 6×10 -18 m 2 . For details about physical and mechanical properties of the Gonghe granite we refer to previous studies (Ji et al, 2021;Zhuang et al, 2022). Granite cores with fixed diameter of 38 mm and varying length of 90-150 mm containing a mated nature fractures (Fig.…”

Section: Rock Specimenmentioning

confidence: 99%

A preliminary attempt to combine in situ CT measurements with permeability tests of fractured granite cores

ZHUANG,

SUN,

PHAM

et al. 2023

JFST

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We introduced a core-flooding test equipment with the triaxial cell having been made available to in situ computed tomography (CT) scanning. Water flow-through tests were conducted on 38 mm-diameter fractured granite cores containing either saw-cut or rough fractures, subjected to a confining pressure varying from 5 to 20 MPa in a single loading-unloading cycle. We put a particular focus on fracture deformation and hydraulic performance of multiple fractures that were artificially assembled to form different fracture interconnection. Results show that in all the cases the permeability of the fractured granite cores nonlinearly decreases with increasing confining pressure, and was reduced by 80-90% when the confining pressure was increased to 20 MPa. Permeability recovery is very limited (10-30%) when the specimen was unloaded to the initial confining pressure of 5 MPa. Poorly-connected fractures show approximately half permeability of the well-connected fractures. Nonuniform deformation including changes in aperture and contact area in natural fractures were observed through CT image analysis. In the end, advantages and limitations of in situ imaging for quantitatively evaluating hydro-mechanical behavior of granite fractures at core-scale were discussed.

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Section: Rock Specimenmentioning

confidence: 99%

A preliminary attempt to combine in situ CT measurements with permeability tests of fractured granite cores

ZHUANG,

SUN,

PHAM

et al. 2023

JFST

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“…However, an increased prevalence of shear cracks has been observed within the intact matrix of coarse-grained rocks, such as crystalline granites, which has been substantiated through microscopic imaging (Zhuang and Zang 2021). More work has been attracted by understanding the shearing effect on rocks in relation to not only large faults or bedding planes but also micro-scale defects in intact materials (Ishida, et al 2000;Rathnaweera et al 2020;Zhuang et al 2022). Nevertheless, the spatial distribution and temporal evolution of these newly found shear cracks have not been well characterized.…”

Section: Introductionmentioning

confidence: 99%

Evolution of Crack Source Mechanisms in Laboratory Hydraulic Fracturing on Harcourt Granite

Zhang,

Si,

et al. 2024

Rock Mech Rock Eng

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Hydraulic fracturing has gained escalating significance in recovering unconventional reservoirs. However, the failure mechanism and its evolution with progressive fluid injection are not fully understood for granitic materials. To investigate, triaxial hydraulic fracturing on Harcourt granite and acoustic emission (AE) monitoring was performed by the self-developed multi-physical rock testing platform (MRTP). Source mechanism analysis suggests that tensile cracks account for the majority (62%) of all cracks throughout the hydraulic fracturing process. Tensile cracks with large energy are induced mainly around the borehole bottom, but their average energy is smaller than shear cracks. The entire hydraulic fracturing process is divided into three stages by injection measurements. In Stage 1, AE events are recorded with low energy emissions but high signal-to-noise ratios, revealing the initiation of hydraulic fractures before peak injection pressure. Tensile cracks are more dominant (78%) than other stages. In Stage 2, the number and magnitude of AE events increase exponentially along the trace formed in Stage 1. In Stage 3, hydraulic fractures have the largest magnitude among all stages. Shear cracks are nearly the same proportion as Stage 2, but more shear cracks with large magnitudes are observed following the trace formed by tensile cracks. A dense population of shear cracks can be found at the borehole bottom, and their distribution follows the average slip plunge of individual shear cracks induced by the injection fluid.

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“…Understanding rock tensile cracking behaviors is significant for various engineering applications. For example, in enhanced geothermal systems (EGS) and oil & gas production (S. Li et al., 2022; L. Zhuang et al., 2022), the fracture initiation and propagation mechanisms of hydraulic fracturing need to be revealed for enhancing energy recovery. In addition, to predict disasters occurring in rock mass, such as wellbore breakouts (Haimson, 2007; Martin et al., 1994), and rock slope slippage (Yuan et al., 2021), the rock cracking process requires in‐depth investigation.…”

Section: Introductionmentioning

confidence: 99%

“…

Understanding rock tensile cracking behaviors is significant for various engineering applications. For example, in enhanced geothermal systems (EGS) and oil & gas production (S. Li et al, 2022;L. Zhuang et al, 2022), the fracture initiation and propagation mechanisms of hydraulic fracturing need to be revealed for enhancing energy recovery.

…”

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confidence: 99%

Mode I Microscopic Cracking Process of Granite Considering the Criticality of Failure

Mo,

Zhao,

Zhang

2023

JGR Solid Earth

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Rock failure under tensile loading conditions is significant for rock engineering stability and underground energy development. However, a comprehensive understanding of the rock cracking process and the corresponding failure pattern at microscale remains unclear. Therefore, the cracking process and the damage evolution of rock and their underlying mechanisms were systematically investigated. In this study, the fracture behavior of granite was examined by performing mode I fracture tests. For extensive analysis of the cracking process, the cracks were captured in real‐time by scanning electron microscope, and the two fracture toughnesses of the double‐K model were evaluated. Subsequently, fracture morphologies of the post‐failure specimens were analyzed to further investigate the cracking mechanisms. The experimental results indicated the following: (a) the propagated direction of cracks was controlled by the fracture toughness of mineral grains and grain boundaries; and (b) the ratio of the two fracture toughnesses was correlated with fracture tortuosity. Furthermore, two damage modes of granite were found: catastrophic failure and non‐catastrophic failure modes. The former showed precursory behavior prior to catastrophic failure, while the latter did not. The underlying mechanisms of damage modes were revealed as follows: (a) the increased degree of heterogeneity caused by mineral composition complexity led to the early arrival of precursors; and (b) the occurrence of catastrophic or non‐catastrophic failure mode was determined by the difference in grain‐scale heterogeneity. Our results found at microscale also have implications for understanding the macroscopic failure process of rocks.

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Grain-scale analysis of fracture paths from high-cycle hydraulic fatigue experiments in granites and sandstone

Cited by 14 publications

References 51 publications

A preliminary attempt to combine in situ CT measurements with permeability tests of fractured granite cores

A preliminary attempt to combine in situ CT measurements with permeability tests of fractured granite cores

Evolution of Crack Source Mechanisms in Laboratory Hydraulic Fracturing on Harcourt Granite

Mode I Microscopic Cracking Process of Granite Considering the Criticality of Failure

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