Brittleness evaluation of coal based on statistical damage and energy evolution theory

Li, Yuwei; Long, Min; Zuo, Lihua; Li, Wenyuan; Zhao, Wanchun

doi:10.1016/j.petrol.2018.08.069

Cited by 116 publications

(50 citation statements)

References 19 publications

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“…In the early stage of uniaxial compression, the stress at the midpoint between the two coal sample ends significantly increased, thereby causing the plastic phase to dominate in this area. It shows obvious brittleness characteristics and is basically the same as the laboratory test results of Li et al 40,41 The sharp decreases in stress and more block yield (new fracture generation) caused the overall permeability of the coal samples to sharply increase. The permeability of the coal sample was found to be highly correlated with the plastic zone (fracture development) and stress, and the permeability of the elastic block gradually decreased as the stress increased.…”

Section: Resultssupporting

confidence: 75%

“…When the stress on the coal sample reached its peak value, the plastic zone connected each other, and a tensile fracture occurred at the junction of the elastic and plastic zones (similar to the X-type region). It shows obvious brittleness characteristics and is basically the same as the laboratory test results of Li et al 40,41 The sharp decreases in stress and more block yield (new fracture generation) caused the overall permeability of the coal samples to sharply increase. In the residual stress phase, the continuous reduction of stress and development of new fractures caused the permeability of the coal sample to continuously increase.…”

Section: Resultssupporting

confidence: 75%

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A fluid‐solid coupling method for the simulation of gas transport in porous coal and rock media

Zhang

Liu

Zhao

et al. 2019

Energy Science & Engineering

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Understanding coal and rock permeability, and the corresponding influence on stress, is important in the field of energy development. In applied engineering, there is a tendency to employ three‐dimensional methods that are simpler, less time‐ and cost‐expensive, less computationally expensive, and larger scale. Thus, a numerical simulation fluid‐solid coupling method is proposed in this paper. The proposed numerical simulation method utilizes the stress‐permeability test results for elastic and plastic coal samples. The permeability models of the elastic and plastic coal samples under loading and unloading were obtained by fitting the experimental results and embedded them into FLAC3D software by using FISH language. The results of the uniaxial and triaxial flow simulations are consistent with the experimental results, thereby confirming the accuracy and feasibility of the numerical method proposed in this paper. This allows the permeability of the numerical reservoir model to be continuously updated according to the current stress level in the production process.

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Section: Resultssupporting

confidence: 75%

Section: Resultssupporting

confidence: 75%

A fluid‐solid coupling method for the simulation of gas transport in porous coal and rock media

Zhang

Liu

Zhao

et al. 2019

Energy Science & Engineering

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show abstract

“…According to the experimental data from rock uniaxial compression and fatigue deformation, Feng et al put forward a novel approach for measuring critical cracking pressure under cyclic loading. Recently, endless theories for studying rock brittleness and its damage alteration based on the rock energy evolution during loading process have been implemented continuously . Zhang et al studied the impact of confining pressure on the evolution of hysteresis loop under pulsating loading from the perspective of energy.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, endless theories for studying rock brittleness and its damage alteration based on the rock energy evolution during loading process have been implemented continuously. [39][40][41][42][43][44] Zhang et al 45 studied the impact of confining pressure on the evolution of hysteresis loop under pulsating loading from the perspective of energy. The results show that both energy consumption in each cycle and energy for crack propagation would increase with the increment of confining pressure.…”

Section: Introductionmentioning

confidence: 99%

Rock damage evolution model of pulsating fracturing based on energy evolution theory

Zhao²,

Tang

et al. 2019

Energy Science & Engineering

Self Cite

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Pulsating fracturing, as a new technology for unconventional oil and gas exploration, enables to enhance stimulated reservoir volume (SRV) effectively, which further helps to improve well performance. It is of great importance for the evaluation of fracturing performance and optimization of fracturing parameters by accurately calculating variables from formation impairment during pulsating fracturing treatment. Based on the principle of conservation of energy, a novel theoretical model describing the evolution of rock damage was proposed by analyzing energy evolutionary characteristics from the hysteresis loop of rock stress‐strain curve while the treatment. This model was in a good agreement with experimental data. In this paper, our study indicates that the rock damage is caused by the accumulation of damage in each cyclic loading and unloading process during pulsating fracturing. Moreover, the cumulative rock damage would increase with the increment of the number of cyclic loading and unloading. Conversely, the rock strength is negatively correlated with cyclic number. The cumulative damage variable approximates to one as the rock breaks. Additionally, the frequency and the stress level of pulsating fracturing have an obvious impact on the evolution of rock damage. The optimization of these parameters can help to accelerate the rock damage and reduce the corresponding rock strength. The speed of rock damage can be accelerated with the enhancement of the stress level at the later period of the step loading, which facilitates the increment of cumulative damage variable. Our new model provides a guideline for predicting the initial rock damage during pulsating treatment.

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“…Hence, the technology has been increasingly used to promote coalbed methane extraction [3]. Many scholars have carried out experimental [4,5] and theoretical research [6] on hydraulic fracturing, presented some evaluation methods [7,8] of coal brittleness, and established the relevant theoretical model [7,9], which can facilitate the field application of coal fracturing. However, there are few studies on the evaluation of hydraulic fracturing effect, since the hydraulic fracturing still remains in the traditional means, such as drilling bits, water content, and other indicators [10].…”

Section: Introductionmentioning

confidence: 99%

Complex Resistivity Dispersion Characteristics of Water‐Bearing Coal Based on Double Cole‐Cole Model

Lei

Zhao

et al. 2019

Advances in Civil Engineering

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Reservoir fracture evaluation is an important research topic in the coalfield. In recent years, complex resistivity (CR) has been widely used in oil logging and achieved good results, such as permeability evaluation, water saturation (Sw) prediction, and aquifer identification. Therefore, the method has the potential to evaluate coal seam fracture. In the experiment, the real part R and imaginary part X of bituminous and anthracite coal with different Sw were measured by the impedance measuring instrument, then the Double Cole-Cole model was used to fit experimental data and analyze conductive mechanism. The main results are as follows: (1) the dispersion of CR parameters Reρ and Imρ is closely related to the metamorphism degree, frequency, and Sw; (2) induced polarization is the fundamental reason for the variation of coal samples’ complex resistivity parameters with frequency change; and (3) the Double Cole-Cole model agrees well with the experimental data, and the model parameters m1 and τ2 are strongly correlated with Sw. The parameters m1 and τ2 can be used to evaluate the Sw of fractures in coal seams and thus to evaluate the effect of hydraulic fracturing.

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Brittleness evaluation of coal based on statistical damage and energy evolution theory

Cited by 116 publications

References 19 publications

A fluid‐solid coupling method for the simulation of gas transport in porous coal and rock media

A fluid‐solid coupling method for the simulation of gas transport in porous coal and rock media

Rock damage evolution model of pulsating fracturing based on energy evolution theory

Complex Resistivity Dispersion Characteristics of Water‐Bearing Coal Based on Double Cole‐Cole Model

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