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Author

Jun Zhang

Bio: Jun Zhang is an academic researcher from Northeast Petroleum University. The author has contributed to research in topics: Brittleness & Fracture (geology). The author has an hindex of 7, co-authored 10 publications receiving 311 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors proposed an evaluation method of brittleness index based on energy method, established the evaluation model based on three types of damage constitutive relations, and finally analyzed the effects of the damage variable of peak strain of different types of different rocks on brittiness.

169 citations

Journal ArticleDOI
Chi Ai1, Jun Zhang1, Yuwei Li1, Jia Zeng1, Xin-liang Yang1, Ji-gang Wang1 
Abstract: Brittleness is one of the most important mechanical properties of rock: it plays a significant role in evaluating the risk of rock bursts and in analysis of borehole-wall stability during shale gas development. Brittleness is also a critical parameter in the design of hydraulic fracturing. However, there is still no widely accepted definition of the concept of brittleness in rock mechanics. Although many criteria have been proposed to characterize rock brittleness, their applicability and reliability have yet to be verified. In this paper, the brittleness of rock under compression is defined as the ability of a rock to accumulate elastic energy during the pre-peak stage and to self-sustain fracture propagation in the post-peak stage. This ability is related to three types of energy: fracture energy, post-peak released energy and pre-peak dissipation energy. New brittleness evaluation indices B 1 and B 2 are proposed based on the stress–strain curve from the viewpoint of energy. The new indices can describe the entire transition of rock from absolute plasticity to absolute brittleness. In addition, the brittle characteristics reflected by other brittleness indices can be described, and the calculation results of B 1 and B 2 are continuous and monotonic. Triaxial compression tests on different types of rock were carried out under different confining pressures. Based on B 1 and B 2, the brittleness of different rocks shows different trends with rising confining pressure. The brittleness of red sandstone decreases with increasing confining pressure, whereas for black shale it initially increases and then decreases in a certain range of confining pressure. Granite displays a constant increasing trend. The brittleness anisotropy of black shale is discussed. The smaller the angle between the loading direction and the bedding plane, the greater the brittleness. The calculation B 1 and B 2 requires experimental data, and the values of these two indices represent only relative brittleness under certain conditions. In field operations, both the relative brittleness and the brittleness obtained from seismic data or mineral composition should be considered to gain a more comprehensive knowledge of the brittleness of rock material.

102 citations

Journal ArticleDOI
TL;DR: In this article, a new index for evaluating coal brittleness was established from the perspective of energy evolution during coal failure, and the applicability of the new index and the influence of the confining pressure and cleat orientation on the coal brittleness were analyzed.
Abstract: Evaluating the ability of coal seams to form fracture networks by hydraulic fracturing is important for the development of coalbed methane (CBM) reservoirs. In this paper, a new index for evaluating coal brittleness was established from the perspective of energy evolution during coal failure. Uniaxial and triaxial compression tests of coal monitored by an acoustic emission (AE) system were carried out and the applicability of the new index and the influence of the confining pressure and cleat orientation on the coal brittleness were analyzed. The pre-peak and post-peak dissipated energies were the essential factors in determining the coal brittleness. The new index can characterize the influence of the external stress and cleat orientation on coal brittleness, and can also comprehensively reflect the mechanical properties of the coal during the pre-peak and post-peak stages. The corresponding AE energy curves can be divided into Rapid Fracture Type, Stable Fracture Type and Plastic Fracture Type. For the Rapid Fracture Type, the accumulation rate of AE energy showed sudden changes when reaching the yield stress and peak strength, which represented high brittleness. The Plastic Fracture Type represented low brittleness, and the accumulated AE energy curves were smooth—first concave and then convex. The brittleness index of coal studied in this paper can provide a new method for selecting the optimal CBM reservoir and optimizing the fracturing scheme.

87 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the fracture propagation behavior in fixed-point multistage fracturing, and the influences of various factors on fracture geometries were studied, including in-situ stress, rock heterogeneity, injection rate and other factors.

59 citations

Journal ArticleDOI
TL;DR: In this paper, the influence of closed cemented natural fractures on the propagation behavior of hydraulic fracture (HF) in tight sandstone formations is studied based on triaxial hydraulic fracturing experiments with acoustic emission (AE) monitoring technology.

59 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors proposed an evaluation method of brittleness index based on energy method, established the evaluation model based on three types of damage constitutive relations, and finally analyzed the effects of the damage variable of peak strain of different types of different rocks on brittiness.

169 citations

Journal ArticleDOI
TL;DR: In this paper, the authors developed an integrated evaluation model through the analyses of a significant amount of actual historical data, which includes six subcomponent models, ranging from the subsurface reservoir to infield flowline.

167 citations

Journal ArticleDOI
TL;DR: In this article, a coupled flow-stress-damage (FSD) model of hydraulic fracture propagation with gravels is established, and the result provides the theoretical support for prediction of fracture propagation morphology and plan design of hydraulic fracturing in the glutenite reservoirs.

130 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the energy evolution characteristics of rock materials under uniaxial compression, and the results showed that all three energy density parameters above increased nonlinearly with increasing unloading stress level as quadratic polynomial functions.
Abstract: To investigate the energy evolution characteristics of rock materials under uniaxial compression, the single-cyclic loading–unloading uniaxial compression tests of four rock materials (Qingshan granite, Yellow sandstone, Longdong limestone and Black sandstone) were conducted under five unloading stress levels. The stress–strain curves and failure characteristics of rock specimens under the single-cyclic loading–unloading uniaxial compression tests basically corresponded with those of under uniaxial compression, which indicates that single-cyclic loading–unloading has minimal effects on the variations in the loading–deformation response of rocks. The input energy density, elastic energy density and dissipated energy density of four rocks under five unloading stress levels were calculated using the graphical integration method, and variation characteristics of those three energy density parameters with different unloading stress levels were explored. The results show that all three energy density parameters above increased nonlinearly with increasing unloading stress level as quadratic polynomial functions. Meanwhile, both the elastic and dissipated energy density increased linearly when the input energy density increased, and the linear energy storage and dissipation laws for rock materials were observed. Furthermore, a linear relationship between the dissipated and elastic energy density was also proposed. Using the linear energy storage or dissipation law, the elastic and dissipated energy density at any stress levels can be calculated, and the internal elastic (or dissipated) energy density at peak compressive strength (the peak elastic and dissipated energy density for short) can be obtained. The ratio of the elastic energy density to dissipated energy density with increasing input energy density was investigated using a new method, and the results show that this ratio tends to be constant at the peak compressive strength of rock specimens.

130 citations

Journal ArticleDOI
TL;DR: In this article, a new brittleness evaluation method was proposed based on promising energy transformation analysis of the complete stress-strain behavior of rock under compression, which is capable of dealing with the plastic energy dissipation mechanisms in the pre-peak region and the extent and rate to which rock strength degrades during macroscopic fracturing in the post-peak stage.

112 citations