A study of hardness and fracture propagation in coal

Klawitter, Matthias; Esterle, Joan; Collins, Sarah

doi:10.1016/j.ijrmms.2015.02.006

Cited by 26 publications

(24 citation statements)

References 19 publications

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“…where τ is shear stress, c is cohesive force, and φ is the internal friction angle. According to the result of the expression in equation (11), the larger the porosity and volume strain of coal rock, the greater the shear stress inside. Let us evaluate the stress state of a representative elementary volume of a coal sample through its Mohr circle.…”

Section: Mechanical Properties Of Bump-prone Coal With DI Erentmentioning

confidence: 99%

“…However, the actual shear stress growth induced by the initial damage is increased, and there is volume expansion until a situation in which shear failure may occur. e Mohr circle of the coal sample is expressed in the red line, its radius by equation (11). e higher the porosity of the coal, the larger the radius of the Mohr circle.…”

Section: Mechanical Properties Of Bump-prone Coal With DI Erentmentioning

confidence: 99%

“…e degree of fracture development directly affects the characterization of the mechanical behaviour of coal. Klawitter et al [11] showed that the mechanical behaviour relates to rank and can control fracture as well as breakage behaviour of a given coal. e original cracks play an important role in the elastic-plastic evolution of coal failure.…”

Section: Introductionmentioning

confidence: 99%

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Mechanical Properties of Bump‐Prone Coal with Different Porosities and Its Acoustic Emission‐Charge Induction Characteristics under Uniaxial Compression

Ding

Xiao

et al. 2019

Advances in Civil Engineering

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Discreteness of mechanical property affected by the intimal damage, which emerged with various degrees of material composition and geological structure, is the difference in porosity macroscopically. Although various porosities directly affect fracture activity, damage evolution and mechanical behaviour of coal bring on the bump-prone assessment error, and disaster happened “ahead of time” in deep underground energy source exploration, little research to date has focused on them. In this paper, the mechanical properties of bump-prone coal samples with different porosities were studied by uniaxial compression test and the initial damage caused by gangue and organic fracture in coal observed by CT. The result indicated that the evolution of coal strength and the logarithm of porosity were expressed by a linear negative correlation and the elastic modules decreased with the initial damage increased. A new quantitative description of damage variables is established by theoretical derivation to reflect the process of cracks formation and expiation in coal, based on volumetric strain and initial porosity. According to the Mohr–Coulomb principle, the effective stress of coal sample with higher the porosity is more likely to reach the shear strength and destruction. The amplitudes and accumulation of AE energy and charge pulse indeed vary with the stress loading stages and strength. The frequency of AE waveform is dominated in three bands (1∼50 kHz, 100∼150 kHz, and 175∼200 kHz) and that of charge induction had one frequency band 1∼100 Hz, and the amplitudes of time domain and main frequency components increased with stress improved. Both of them originated from cracks and belong to homologous signals, crack development bound to be accompanied by stress wavelet, not necessarily free charge; meanwhile, charge pulse being emerged means there must be cracks interaction and the acoustic emission signals are generated prior to charge induction.

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Section: Mechanical Properties Of Bump-prone Coal With DI Erentmentioning

confidence: 99%

Section: Mechanical Properties Of Bump-prone Coal With DI Erentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Mechanical Properties of Bump‐Prone Coal with Different Porosities and Its Acoustic Emission‐Charge Induction Characteristics under Uniaxial Compression

Ding

Xiao

et al. 2019

Advances in Civil Engineering

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“…Stress sensitivity, comprehensive filtration coefficient and pumping delivery capacity were the key factors affecting the fracture length 15 . Klawitter et al 16 analysed the fractures resulting in coal using the shore scleroscope rebound hardness test, which can be scaled up to understand fracture propagation in CBM reservoirs. Li and Xing 17 studied the effect of formation properties on the hydraulic fracture initiation.…”

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confidence: 99%

Impact Analysis of Multiple Parameters on Fracture formation during Volume Fracturing in Coalbed Methane Reservoirs

Jiang

Zhang

2017

Current Science

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Uniaxial and triaxial compression, Brazilian splitting and three-point bending tests have been carried out to determine the mechanical parameters of the coal reservoir in Jiaozuo coal mining district, Henan Province, China. Based on the experimental results and combined with the target reservoir geological characteristics, a 3D geological mechanical model has been established to analyse the hydraulic fracture propagation during volume fracturing using MEYER software. Effects of the modulus of coal rock, difference between horizontal principal stresses, fracturing fluid viscosity and fracturing fluid injection rate on the fracturing network geometry are studied. Results show that fracturing network development intensity in the coalbed methane (CBM) reservoir is determined both by the geological conditions and the hydraulic fracturing parameters. The intensity of fracturing in the CBM reservoir is positively related with the elastic modulus of the coal rock, and is inversely proportional to the difference between the two horizontal principal stresses. Increasing fluid viscosity reduces the fracturing area. Low injection rate is beneficial to improving hydraulic treatment areas when it is larger than that required to guarantee that the crack extends. The results can provide a case reference for optimization design of volume fracturing and productivity prediction analysis of CBM reservoirs.Keywords: Coalbed methane reservoir, fracture network, numerical simulation, volume fracturing.IN volume fracturing, the resulting fracture network geometry is mainly determined by the in situ stress and rock physical and mechanical properties (elastic modulus, Poisson ratio, tensile strength and fracture toughness). In addition, the fracturing implementation parameters (such as construction scale, capacity, viscosity and filtration of fracturing fluid, etc.) affect fracture geometry to a certain extent 1,2 . Coalbed methane (CBM) reservoirs contain a large number of pores 3 , which make the fracture geometry more complicated. The analysis of fracture network geometry can guide an efficient exploitation of CBM and be of significance on the later evaluation of fracturing effectiveness 4,5 . Volume fracturing as a new kind of fracturing technology is totally different from conventional hydraulic fracturing. It makes full use of the formation bedding and natural fractures to produce a number of transverse and longitudinal artificial fractures which communicate with the natural fracture system away from the wellbore. It is intended to further expand the discharge area, rather than to control the expansion of natural fractures 6,7 . The volume fracturing technology will most likely communicate further natural fractures and form a larger seepage scope 8,9 . It will exert the advantages of the natural fracture network to increase production and enhance matrix supply capacity. It will also improve the stimulation effect and have importance in unconventional reservoir recovery.Coal rock mechanics parameters are the prerequisites of CBM res...

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“…Variation of median corrected specific fracture energy for sub-bituminous coal on SILC influenced by shape. (Klawitter et al, 2015). xx showing location of transects as well as distinct lithotypes delineated.…”

Section: Figurementioning

confidence: 99%

Alternative methods for geomechanical characterisation of sub-bituminous coal, Surat Basin, Australia

Barbosa¹

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A study of hardness and fracture propagation in coal

Cited by 26 publications

References 19 publications

Mechanical Properties of Bump‐Prone Coal with Different Porosities and Its Acoustic Emission‐Charge Induction Characteristics under Uniaxial Compression

Mechanical Properties of Bump‐Prone Coal with Different Porosities and Its Acoustic Emission‐Charge Induction Characteristics under Uniaxial Compression

Impact Analysis of Multiple Parameters on Fracture formation during Volume Fracturing in Coalbed Methane Reservoirs

Alternative methods for geomechanical characterisation of sub-bituminous coal, Surat Basin, Australia

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