The Experts below are selected from a list of 16755 Experts worldwide ranked by ideXlab platform
Jia Zeng - One of the best experts on this subject based on the ideXlab platform.
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Energy-Based Brittleness Index and Acoustic Emission Characteristics of Anisotropic Coal Under Triaxial Stress Condition
Rock Mechanics and Rock Engineering, 2018Co-Authors: Jun Zhang, Ming-guang Che, Gao Rui, Jia ZengAbstract: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.
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estimation criteria for rock Brittleness based on energy analysis during the rupturing process
Rock Mechanics and Rock Engineering, 2016Co-Authors: Jun Zhang, Jia Zeng, Xinliang Yang, Jigang WangAbstract: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.
Jun Zhang - One of the best experts on this subject based on the ideXlab platform.
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Energy-Based Brittleness Index and Acoustic Emission Characteristics of Anisotropic Coal Under Triaxial Stress Condition
Rock Mechanics and Rock Engineering, 2018Co-Authors: Jun Zhang, Ming-guang Che, Gao Rui, Jia ZengAbstract: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.
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evaluation method of rock Brittleness based on statistical constitutive relations for rock damage
Journal of Petroleum Science and Engineering, 2017Co-Authors: Dan Jia, Zhenhua Rui, Jiyong Peng, Jun ZhangAbstract:Abstract Brittleness is an important feature of rock and is related to many mechanical behavior of rock. An accurate evaluation of rock Brittleness lays an analytical foundation of drilling and hydraulic fracturing. At present, there are several evaluation methods of rock Brittleness, but none of them has taken the evolution of internal damage into consideration during the loading process, and thus will not effectively indicate the influence of damage on Brittleness during loading. We have conducted a series of uni-axial compressive tests on coal rock, shale and tight sand, and have obtained the stress-strain curves of different types of rock. Then we have established the damage constitutive model of micro damage for each type of rock based on power function distribution, Weibull distribution and Gaussian distribution. We have proposed an evaluation method of Brittleness index based on energy method, established the evaluation model of Brittleness based on three types of damage constitutive relations, and have finally analyzed the effects of the damage variable of peak strain of different rocks on Brittleness. The results of this paper have proved that the damage constitutive model of micro damage can effectively describe the stress strain curves of different rocks before the peak strength. On the other hand, it indicates that the increase of damage variable of peak strain will undermine rock Brittleness, and the relation between Brittleness and damage variable of peak strain obeys different rules of the three types of damage constitutive models damage constitutive model based on Gaussian distribution benefits evaluation of Brittleness of different types of rock, and based on power function distribution makes for the same types of rock. This paper has proposed a fresh perspective of studying Brittleness, the results of which will improve the present evaluation methods and enrich our understanding of rock Brittleness.
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estimation criteria for rock Brittleness based on energy analysis during the rupturing process
Rock Mechanics and Rock Engineering, 2016Co-Authors: Jun Zhang, Jia Zeng, Xinliang Yang, Jigang WangAbstract: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.
E. K. Chanda - One of the best experts on this subject based on the ideXlab platform.
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Fracture Energy-Based Brittleness Index Development and Brittleness Quantification by Pre-peak Strength Parameters in Rock Uniaxial Compression
Rock Mechanics and Rock Engineering, 2016Co-Authors: H. Munoz, A. Taheri, E. K. ChandaAbstract:Brittleness is a fundamental mechanical rock property critical to many civil engineering works, mining development projects and mineral exploration operations. However, rock Brittleness is a concept yet to be investigated as there is not any unique criterion available, widely accepted by rock engineering community able to describe rock Brittleness quantitatively. In this study, new Brittleness indices were developed based on fracture strain energy quantities obtained from the complete stress–strain characteristics of rocks. In doing so, different rocks having unconfined compressive strength values ranging from 7 to 215 MPa were examined in a series of quasi-static uniaxial compression tests after properly implementing lateral-strain control in a closed-loop system to apply axial load to rock specimen. This testing method was essential to capture post-peak regime of the rocks since a combination of class I–II or class II behaviour featured post-peak stress–strain behaviour. Further analysis on the post-peak strain localisation, stress–strain characteristics and the fracture pattern causing class I–II and class II behaviour were undertaken by analysing the development of field of strains in the rocks via three-dimensional digital image correlation. Analysis of the results demonstrated that pre-peak stress–strain Brittleness indices proposed solely based on pre-peak stress–strain behaviour do not show any correlation with any of pre-peak rock mechanical parameters. On the other hand, the proposed Brittleness indices based on pre-peak and post-peak stress–strain relations were found to competently describe an unambiguous Brittleness scale against rock deformation and strength parameters such as the elastic modulus, the crack damage stress and the peak stress relevant to represent failure process.
Iman Rahimzadeh Kivi - One of the best experts on this subject based on the ideXlab platform.
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an investigation on the effect of thermal maturity and rock composition on the mechanical behavior of carbonaceous shale formations
Marine and Petroleum Geology, 2020Co-Authors: Atefeh Vafaie, Iman Rahimzadeh KiviAbstract:Abstract An accurate assessment of the geomechanical behavior of shale reservoirs is extremely significant in screening the potential intervals for hydraulic stimulation and sweet spot mapping. While most of the studies were carried out on siliciclastic shales, we here examine the mechanical behavior of a carbonaceous organic-rich shale in the Lurestan Basin, Iran, and the factors controlling them. Direct laboratory measurements at reservoir stress conditions (static method) and well-logging interpretations (dynamic approach) were employed to assess the main geomechanical properties. Besides, various experimental techniques have been employed to evaluate the dominant shale mineralogy, geochemical properties and rock fabric. It is observed that Young's modulus and Poisson's ratio, obtained from either static or dynamic approaches, are capable of reflecting rock Brittleness. Conducted sensitivity analyses also reveal that abundances of organic matter, clay and carbonate minerals are the most significant factors controlling rock Brittleness. An increase in the Brittleness is envisioned by increasing the carbonate content and inversely by decreasing the concentrations of clay minerals and organic matter. Moreover, week or no clear relationship regarding the possible effects of thermal maturity and quartz content could be distinguished. Incorporating the distinguished controlling factors into a compositional index, a similar relative Brittleness sequence with the elasticity-based approach was detected. This indicates that both independent methods are suitable for the identification of brittle layers. Inspected shale samples illustrate notably higher strengths in comparison with well-characterized organic-rich shales in the world, translated as a direct contribution of firm carbonate textures to the rock framework. Taking these textures together with the main mineral contents into account, the reservoir can be subdivided into three lithofacies including limestone, argillaceous limestone and micritic limestone. Micritic limestones show relatively higher strength and Brittleness, whereas limestone and argillaceous limestone facies, in spite of high variability, reflect in average lower strength and brittle characteristics.
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shale Brittleness evaluation based on energy balance analysis of stress strain curves
Journal of Petroleum Science and Engineering, 2018Co-Authors: Iman Rahimzadeh Kivi, Mohammad Javad Ameri, Hamed MolladavoodiAbstract:Abstract Brittleness is a key mechanical characteristic of rock and critical to various engineering practices particularly to design efficient fracturing stimulation of unconventional shale gas reservoirs. Variety of Brittleness definitions and evaluation criteria have been proposed to describe rock failure behavior; however, their suitability and reliability have yet to be verified. In this paper, the existing Brittleness indices were reviewed in detail and their applicability to reflect rock brittle characteristics were then investigated. The analysis indicated that most of expressions cannot describe brittle failure characteristics of rock efficiently and either partially or thoroughly fail to correctly address the impact of stress state on rock Brittleness. Therefore, a new Brittleness evaluation method was proposed based on promising energy transformation analysis of the complete stress-strain behavior of rock under compression. The new criterion 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. Besides, the proposed Brittleness index describes the entire transition of rock failure behavior of class I, from completely plastic to absolutely brittle states, in a continuous scale corresponding to 0 to 1. The applicability and outperformance of the proposed Brittleness index were then verified against uniaxial and triaxial compression test results of some carbonaceous lithofacies from the Garau shale gas play within the Lurestan Basin, Iran. Samples under compression revealed various deformation and failure characteristics transitioned from brittle to semi-brittle behaviors with increasing confining pressure. Application of the Brittleness indices to the tested rock specimens clearly demonstrated that the developed energy-based expression is able to rigorously capture the relative Brittleness sequences of lithofacies and evolution trends under application of confinement, whereas further proved lack of either sufficient physical basis or appropriate formulation strategy in the existing indices. Accordingly, the new evaluation method seems to provide reliable estimates of rock Brittleness in various field practices even though further verification is necessary. Finally, the important relation between microstructural carbonaceous texture and rock Brittleness was discussed.
Jigang Wang - One of the best experts on this subject based on the ideXlab platform.
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estimation criteria for rock Brittleness based on energy analysis during the rupturing process
Rock Mechanics and Rock Engineering, 2016Co-Authors: Jun Zhang, Jia Zeng, Xinliang Yang, Jigang WangAbstract: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.