A numerical model for outburst including the effect of adsorbed gas on coal deformation and mechanical properties

Coal permeability is a key parameter that affects the drainage of coal bed methane (CBM). Owing to the lower original permeability of coal seams in China, more attention was paid to the study of damage‐induced permeability laws. However, the theory of damage‐induced permeability still needs to be improved. In this paper, the permeability evolution experiments during the complete stress–strain process of coal were carried out firstly. The results are shown that with the increase in axial strain, the coal permeability decreases slowly at first, then increases rapidly, and finally increases slowly or even remains unchanged, and the peak stress point can be regarded as the extreme point of permeability. Then, the equivalent plastic strain was used to describe the damage of coal. Based on the above results, a new damage‐induced permeability model was developed, and the new model can match the experimental data of permeability very well. In addition, solid–gas coupling models of coal were developed based on the new permeability model, and the numerical results show that there is a region of sudden increase in permeability around the borehole where plastic failure occurs, which indicates that the damage‐induced permeability model is reasonable. Finally, the results of numerical simulation of gas predrainage in combination of soft coal and hard coal under different cases were used to optimize the borehole layout of gas predrainage in the field.

Section: Damage‐induced Permeability Modelmentioning

confidence: 99%

Damage‐induced permeability model of coal and its application to gas predrainage in combination of soft coal and hard coal

Zhang

et al. 2019

“…After hydraulic caving, the permeability of the coal around the cave will change accordingly, the governing equation of permeability change can be expressed as follows:

k = \{\begin{matrix} k_{0} e^{- ω I_{1}}, & γ^{p} = 0 \\ k_{0} (1 + \frac{γ^{p}}{γ^{p *}} ξ) e^{- ω I_{1}}, & 0 < γ^{p} < γ^{p *} \\ k_{0} (1 + ξ) e^{- ω I_{1}}, & γ^{p} \geq γ^{p *} \end{matrix}

where

k_{0}

is the initial permeability of the coal seam,

ω

is the cleat volume compressibility, and

ξ

is the jump coefficient of permeability.…”

Section: Numerical Simulation and Laboratory Observationmentioning

confidence: 99%

A new cross‐borehole hydraulic caving technique in the coal seam with a soft layer for preventing coal and gas outbursts during coal roadway excavation

Qin

Wei

Lou

et al. 2020

Predrainage of gas by cross‐boreholes is an important method to prevent coal and gas outbursts in the process of a coal roadway excavation. Limitations of technologies and poor effects of preventing coal and gas outbursts occur in the coal seam with a soft layer. In this study, a new hydraulic caving technology for cross‐boreholes has been proposed to solve this problem. A CT equipment was used to observe the development of coal fissures around cross‐boreholes in the coal seam with a soft layer. The plastic zone range and permeability distribution of ordinary hydraulic slotting technologies and the new hydraulic caving technology also were compared by numerical simulation. The field test of hydraulic caving was taken in the Xuehu Mine (China). The results show that the fracture development degree of soft coal is greater than that of hard coal at the same distance from cross‐boreholes. The fracture development degree in the plastic zone is greater than that in the elastic zone. The hydraulic caving technique can achieve the same effect as the ordinary hydraulic slotting with less workload. The mass of coal discharged from a cross‐borehole was 1.15 t/m and the average methane concentration of single drainage borehole increased by 1.09‐4.1 times, and the average methane extraction amount of single drainage borehole increased by 6.06 times. Elimination of coal and gas outburst had been completed after 110 days of extraction in the area of hydraulic caving, and Q and S values are lower than the critical value during roadway excavation. It is conclusion that hydraulic caving technique can effectively improve the permeability and rapidly eliminate coal and gas outburst in the coal seam with a soft layer.

“…Furthermore, it has been proved that the high pressure gradient produced by a large volume of gas desorbed within a short period is an essential condition to push the crushed coal into the mining space. 1,[3][4][5][6] According to the theory of the comprehensive effect of coal, gas, and crustal stress, the gas pressure is the power source of coal and gas outburst, and the adsorption and desorption characteristics of coal partly determine the gas occurrence and gas pressure, which affect the probability and | 975 WANG et Al. level of the coal and gas outburst accidents.…”

Section: Introductionmentioning

confidence: 99%

Correlation between coal and gas outburst risk and adsorption properties of coal seams

Wang

Zou

2019

Based on the Langmuir adsorption model, the adsorption constants of eighteen coal samples from the same coal mine with outburst risk, weak outburst risk, and non‐outburst risk were tested by high‐pressure capacity method under different temperature conditions. The results show that the adsorption constants a and b monotonically decrease with the increase in temperature. The relationship between a and temperature shows three stages: accelerated decreasing stage, decelerated decreasing stage, and stable stage. The b decreases with the increase in temperature also shows three stages, namely relative stability, slow decrease, and accelerated decrease. The a × b for the outburst coal seam decreases with increasing temperature, which is similar to b. The a × b for the weak and non‐outburst coal seams decreases with increasing temperature, which is similar to a. Furthermore, the a of the outburst coal seam decreases with the increase in temperature, and the decrease of b is the largest. The a of the weak and non‐outburst coal seams decreases with the increase in temperature, and the magnitude is relatively large. The b decreases slightly, with a smaller magnitude. The a × b of weak outburst seam is smaller than that of non‐outburst seam and is larger than that of outburst seam. The achievements can provide guiding significance for coal and gas outburst prevention and control.