Acoustic emission characterization of microcracking in laboratory-scale hydraulic fracturing tests

Hampton, Jesse; Gutierrez, Marte; Matzar, Luis; Hu, Dandan; Frash, Luke P.

doi:10.1016/j.jrmge.2018.03.007

Cited by 54 publications

(26 citation statements)

References 15 publications

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“…Yamamoto et al [24] classified hydraulic fracturing into shear-dominant events and tensile/compression-dominant events, by the consistency coefficient, which is a function of the classic moment tensor decomposition (isotropic (ISO), double-couple (DC), and compensated linear vector dipole (CLVD)). Hampton et al [28] categorized AE into shear, tensile, and mixed mode, through manipulating the eigenvalues of the moment tensor matrix. This method has been widely used to identify rock failure under different stress conditions [29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Micro-Crack Mechanism in the Fracture Evolution of Saturated Granite and Enlightenment to the Precursors of Instability

Dong

Zhang

2020

Sensors

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To explore the potential precursors of rock instability, it is necessary to clarify the mechanism of micro-crack from fracturing to failure, which involves the evolution of fracture size, orientation, source model, and their relationships to the loading. The waveforms of acoustic emission (AE) recorded by the sensor network attached rock sample during laboratory tests provide a data basis for solving these problems, since these observations are directly related to the characteristics of the fracturing sources. Firstly, we investigated the source mechanism, looking at the rise angle and the average frequency (RA-AF) trends during five loading stages in a uniaxial compression test. Results show that the proportion of shear events significantly increases when approaching instability. Secondly, we calculated the moment tensor for each event, considering the uncertainties of P-wave polarity, azimuth, and the takeoff angles of the rays. Moment tensor solutions suggest that there are obviously more crack events than shear events in all loading stages. Moment tensor evolutions confirmed that the decreasing of isotropic component and the increment of double-couple can be used as precursors of rock fracturing development. Considering the limitations of these two methods, it is suggested that we should be concerned more about the proportions of individual failure components and their evolutions over time, instead of absolutely classifying the events into a certain source type.

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Section: Introductionmentioning

confidence: 99%

Micro-Crack Mechanism in the Fracture Evolution of Saturated Granite and Enlightenment to the Precursors of Instability

Dong

Zhang

2020

Sensors

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“…Literature review indicates that a variety of fracturing fluids have been used in experiments. ey include oil [76], water [77], guar gum [72], liquid carbon dioxide (L-CO 2 ) [78], supercritical carbon dioxide (SC-CO 2 ) [79], linear gel [80], polymer fluid [68], calcium chloride (CaCl 2 ) solution [81], methyl methacrylate (MMA) [57], nitrogen [10], and bentonite slurry [82]. Moreover, in an experiment, the fracturing fluid is often mixed with a fluorescent compound (Figure 1(c)) for better tracing of hydraulic fractures [83].…”

Section: Fracturing Fluids Fracturing Fluids Play Crucial Roles In Amentioning

confidence: 99%

Advances in Laboratory‐Scale Hydraulic Fracturing Experiments

Qian

Guo

Wang

et al. 2020

Advances in Civil Engineering

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Hydraulic fracturing has been widely applied to stimulate the natural gas and oil production from unconventional reservoirs. To optimize the design of hydraulic fracturing in this application, an accurate estimation of the initiation and propagation of hydraulic fractures is indispensable. However, it still remains challenging as a result of the complex stress state and geological conditions. On account of their ability to complete control some significant factors and efficient observation of fracture geometry, laboratory-scale hydraulic fracturing experiments have received abundant research attention in recent years. This paper presents a review of the state of the art of laboratory-scale hydraulic fracturing experiments, focusing on the scaling analysis, experimental setup, fracturing fluids, and sample preparation. A discussion of the directions for future research is also provided with the intention of stimulating the development of the experimental technique for investigating hydraulic fracturing.

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“…Previous studies related to hydraulic fracturing have divided fractures into primary and secondary fractures [24,25]. For further study, fractures are divided into three types, namely, primary fractures, secondary fractures, and microcracks according to the customary method and the characteristics of various man-made fractures [26,27]. The main classification characteristics of fractures are shown in Table 1.…”

Section: Classification Of Fracturesmentioning

confidence: 99%

Experimental Study of Fracturing Fluid Retention in Rough Fractures

Zhang

et al. 2019

Geofluids

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Multistage hydraulic fracturing is a key technology for developing tight reservoirs. Field data indicate that a small fraction of the injected water can be recovered during flowback. Fractures play an important role in the retention of fracturing fluid, but the mechanisms and rules remain uncertain. Therefore, an experimental facility was established for studying the fluid retention in fractures using an improved conductivity apparatus. The fluid trapped in rough fractures was measured, and the dynamic changes of the drainage volume and rate under various apertures were analyzed. The effects of different factors, such as the fracture aperture, surface roughness, tortuosity, and matrix imbibition, on the fluid retention were studied. An empirical formula between the retention rate and fracture aperture was derived on the basis of mass conservation. Results showed that the fluid retention rate slowly decreased with an aperture increase in the fracture, and it would increase with considerable roughness, high tortuosity, and significant matrix imbibition. Meanwhile, drainage volume and rate change dramatically resulted from the gas drive. Secondary fractures and microcracks played an important role in the retention of fracturing fluid. Furthermore, the mechanisms of fracturing fluid retained in the tight reservoir, including viscous trapping and “locking” in fractures, the effect of gravity, surface-bound water film, capillary force retention, and matrix imbibition, were discussed. This study is significant for understanding the flowback rules of fracturing fluid, diagnosing fracture development, and identifying reservoir properties.

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Acoustic emission characterization of microcracking in laboratory-scale hydraulic fracturing tests

Cited by 54 publications

References 15 publications

Micro-Crack Mechanism in the Fracture Evolution of Saturated Granite and Enlightenment to the Precursors of Instability

Micro-Crack Mechanism in the Fracture Evolution of Saturated Granite and Enlightenment to the Precursors of Instability

Advances in Laboratory‐Scale Hydraulic Fracturing Experiments

Experimental Study of Fracturing Fluid Retention in Rough Fractures

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