Evaluation of the Micro-cracks in Shale from the Stress Sensitivity of Ultrasonic Velocities

Wang, Xiaoqiong; Ge, Hongkui; Wang, Jianbo; Wang, Daobing; Chen, Hao

doi:10.1007/s00603-016-1027-8

Cited by 17 publications

(5 citation statements)

References 16 publications

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“…It offers unique insights into the fracture network and rock interactions (Zhai et al, 2020). Ultrasonic imaging and acoustic emission monitoring are key for real-time monitoring, which can detect energy releases from crack formations (Wang et al, 2016). Moreover, recent hydraulic fracturing experiment studies have improved our understanding of fracture tip progression using distributed acoustic sensing data.…”

Section: Experiments and Acoustic Emission Monitoring In Hydraulic Fr...mentioning

confidence: 99%

Experimental and numerical simulation technique for hydraulic fracturing of shale formations

Huang,

Liao,

Fan

et al. 2024

Adv. Geo-Energy Res.

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Hydraulic fracturing is crucial for extracting shale oil and gas. This technique involves creating fractures in rock formations to enhance reservoir development efficiently. Due to the complexity of shale rock, it is important to conduct multiscale investigations into the fracturing process. Despite extensive research, the technology for deep-underground shale hydraulic fracturing continues to advance as it moves deeper underground. This paper explores the existing technical challenges of shale fracturing, review the current status of physical experiments and numerical simulations, and highlight the importance of multiscale numerical simulation methods. Meanwhile, an integrated approach to optimizing fracturing designs for field cases is introduced. Finally, this paper summarizes the challenges and opportunities in shale hydraulic fracturing, aiming to provide fresh insights into the advancements of hydraulic fracturing technology.

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Section: Experiments and Acoustic Emission Monitoring In Hydraulic Fr...mentioning

confidence: 99%

Experimental and numerical simulation technique for hydraulic fracturing of shale formations

Huang,

Liao,

Fan

et al. 2024

Adv. Geo-Energy Res.

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“…The slope of the fitting line was defined as χ, that is, the stress sensitivity coefficient of the acoustic wave velocity. A larger χ value indicates a stronger stress sensitivity [52].…”

Section: The Stress Sensitivity Of the Acoustic Wave Velocitymentioning

confidence: 99%

Experimental Investigation of Stress Sensitivity of Elastic Wave Velocities for Anisotropic Shale in Wufeng–Longmaxi Formation

Feng,

Tang,

Tang

et al. 2023

Processes

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The shale of the Wufeng–Longmaxi formation in the Sichuan Basin is the preferred layer for shale gas exploration in China, and its petrophysical characteristics are the key to geological and engineering sweet spot prediction. However, the characteristics and impact mechanisms of its acoustic wave velocity and elastic anisotropy are currently unclear. In this paper, the Wufeng–Longmaxi shale is taken as the research object, and the P-wave and S-wave velocities of the samples are tested under the loading and unloading processes of confining pressure. The stress sensitivity variations in parameters such as wave velocity, wave velocity ratio, and anisotropy are discussed. P-wave and S-wave anisotropy parameters are correlated under different pressure conditions. X-ray diffraction, casting thin sections, scanning electron microscopy, micron CT scanning, and other analytical techniques are used to explore the mechanisms of stress sensitivity of elastic parameters. The research results indicate that: (1) the acoustic velocities of samples from different angles are V90° > V45° > V0°, and there is a positive correlation between the wave velocity and the confining pressure. After unloading the confining pressure, irreversible plastic deformation occurs due to the closure of some microfractures in the rock core, causing the wave velocity to be higher than the initial value. (2) The stress sensitivity coefficient of the P-wave (The mean is 3.00 m·s−1·MPa−1) is higher than that of the S-wave (the mean is 1.23 m·s−1·MPa−1), and the stress sensitivity coefficient of the compacted stage (the mean is 3.02 m·s−1·MPa−1) is higher than that of the elastic stage (the mean is 1.21 m·s−1·MPa−1). (3) The anisotropy of the P-wave and S-wave is negatively correlated with the confining pressure. When the confining pressure is loaded to 65 MPa, the change rate of the P-wave anisotropy coefficient is 23%, and its stress sensitivity is higher than that of S-wave anisotropy coefficient (the change rate is 13.7%). After unloading the confining pressure, the degree of anisotropy is reduced due to the closure of some microfractures. The empirical formula of P-wave and S-wave anisotropy parameters under different pressures is established through linear regression, which can provide a reference for mutual predictions. (4) The variation in wave velocity anisotropy with stress can be divided into stress and material anisotropy, which are related to the directional arrangement of microfractures and clay minerals, respectively. The quantitative characterization of shale anisotropy can be realized by evaluating the development degree of reservoir fractures and mineral components, providing a reference for logging interpretations, sweet spot prediction, and fracturing construction of shale gas reservoirs.

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“…It is indicated that ultrasonic features may be used to describe the stress threshold for deep shale fracture initiation and damage. Wang et al 36 pointed out ultrasonic wave velocities are highly sensitive to crack closure and propagation and established a method to characterize the microcrack development in shale samples from the stress sensitivity of ultrasonic velocities. Qu et al 37 investigated the pore structure evolution of deep shales before and after LN 2 freezing based on NMR technology.…”

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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Evaluation of the Micro-cracks in Shale from the Stress Sensitivity of Ultrasonic Velocities

Cited by 17 publications

References 16 publications

Experimental and numerical simulation technique for hydraulic fracturing of shale formations

Experimental and numerical simulation technique for hydraulic fracturing of shale formations

Experimental Investigation of Stress Sensitivity of Elastic Wave Velocities for Anisotropic Shale in Wufeng–Longmaxi Formation

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

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