Solid‐Gas Coupling Model for Coal‐Rock Mass Deformation and Pressure Relief Gas Flow in Protection Layer Mining

Zhu, Zhuohui; Feng, Tao; Yuan, Zhigang; Xie, Dong; Chen, Wei

doi:10.1155/2018/5162628

Cited by 16 publications

(18 citation statements)

References 7 publications

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“…e indicial notation is adopted to express tensor quantities and vector hereafter. For porous coal-rock mass with single-phase saturated, the effective stress σ′ ij (positive for tension), total stress σ ij , and pore pressure p satisfy the modified principle of Terzaghi effective stress [16].…”

Section: Governing Equations For Deformation Fieldmentioning

confidence: 99%

Numerical Modeling on Hydraulic Fracturing in Coal-Rock Mass for Enhancing Gas Drainage

Yuan

Shao

2018

Advances in Civil Engineering

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The mechanism of how hydraulic fracturing influences gas drainage in coal-rock mass is still not clear due to its complex mechanism. In this work, statistical distributions are firstly introduced to describe heterogeneity of coal-rock mass; a novel simultaneously coupled mathematical model, which can describe the fully coupled process including seepage-damage coupling during hydraulic fracturing process and subsequent gas flow during gas drainage process, is established; its numerical implementation procedure is coded into a Matlab program to calculate the damage variables, and it partly uses COMSOL solver to obtain numerical solutions of governing equations with damage-flow coupling; the mathematical model and its implementation are validated for initial damage pressure and mode of a single solid model without considering flow-damage coupling, as well as fracture initiation pressure and influence of heterogeneity on damage evolution of hydraulic fracturing considering flow-damage coupling; and finally, based on an engineering practice of hydraulic fracturing with two boreholes, the mechanism of how hydraulic fracturing influences gas drainage is investigated, numerical simulation results indicate that coal-rock mass pore-fissure structure has been improved, and there would exist a gas migration channel with characteristics of higher porosity and lower stresses, which demonstrates significant effects and mechanism of hydraulic fracturing on improving coal-rock permeability and enhancing gas drainage. The research results provide a guide for operation of hydraulic fracturing and optimal layout of gas drainage boreholes.

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Section: Governing Equations For Deformation Fieldmentioning

confidence: 99%

Numerical Modeling on Hydraulic Fracturing in Coal-Rock Mass for Enhancing Gas Drainage

Yuan

Shao

2018

Advances in Civil Engineering

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“…However, it cannot tell when it is the best to accelerate to abrasive mode to erode the rock and coal, because abrasive acceleration relates not only to gas velocity but also to gas density, viscosity, temperature, pressure gradient, etc. [26][27][28][29]. Furthermore, the inlet pressure is critical to abrasive acceleration and velocity, because it determines the expansion state of the gas jet.…”

Section: Further Optimizing the Laval Nozzlementioning

confidence: 99%

Optimal Nozzle Structure for an Abrasive Gas Jet for Rock Breakage

Liu

Zhang

et al. 2018

Geofluids

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Abrasive gas jet technologies are efficient and beneficial and are widely used to drill metal and glass substrates. When the inlet pressure is increased, gas jets could be powerful enough to break rock. They have potential uses in coal-bed methane exploration and drilling because of their one-of-a-kind nonliquid jet drilling, which avoids water invasion and borehole collapse. Improving the efficiency of rock breakage using abrasive gas jets is an essential precondition for future coal-bed methane exploration. The nozzle structure is vital to the flow field and erosion rate. Furthermore, optimizing the nozzle structure for improving the efficiency of rock breakage is essential. By combining aerodynamics and by fixing the condition of the nozzle in the drill bit, we design four types of preliminary nozzles. The erosion rates of the four nozzles are calculated by numerical simulation, enabling us to conclude that a nozzle at Mach 3 can induce maximum erosion when the pressure is 25 MPa. Higher pressures cannot improve erosion rates because the shield effect decreases the impact energy. Smaller pressures cannot accelerate erosion rates because of short expansion waves and low velocities of the gas jets. An optimal nozzle structure is promoted with extended expansion waves and less obvious shield effects. To further optimize the nozzle structure, erosion rates at various conditions are calculated using the single-variable method. The optimal nozzle structure is achieved by comparing the erosion rates of different nozzle structures. The experimental results on rock erosion are in good agreement with the numerical simulations. The optimal nozzle thus creates maximum erosion volume and depth.

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“…As the depletion of shallow coal resources, coal working face would enter into deep mining area. Related studies show that the mining depth of China would increase to 1500 m in next twenty years [1][2][3]. e in situ stress, gas pressure, or gas content reserved in coal seams would increase with mining depth, thus causing an increase of gas disaster risk which would seriously affect efficiency and safe mining of coal resources.…”

Section: Introductionmentioning

confidence: 99%

Similar Material Simulation Study on Protection Effect of Steeply Inclined Upper Protective Layer Mining with Varying Interlayer Distances

Yuan

Shao

Zhu

2019

Advances in Civil Engineering

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Protective layer mining, as a dominating regional prevention measure, is generally adopted to prevent and control gas disasters in highly gassy or outburst mines of China. Interlayer distance is one of the most important factors that influences protection effect. However, how does interlayer distance affect the protection effect of steeply inclined upper protective layer mining is not understood fully. According to the engineering practice in Nantong mining district, a new method for similar material simulation experiment of steeply inclined upper protective layer mining is proposed, in which an orthogonal test of similar materials comprising of sand, cement (containing gypsum and fly ash), and water mixture is conducted to obtain relations between proportioning parameters and mechanical properties using a multiple regression method. And then the method is applied to study the protection effect of steeply inclined upper protective layer mining with varying interlayer distances. e results show the following. (1) e proportioning parameters of similar material have strong linear relations with its mechanical properties, and mechanical behaviors of such similar material denote that it can simulate most coal-rock lithologies in coal mine. (2) Both pressure-relief curves and swelling strain curves for protected layer present convex shapes; protection angles at lower excavation boundary are greater than those of upper excavation boundary; with the increase of interlayer distance, the pressure-relief curve evolves from pattern "∩" to pattern "∧" and corresponding pressure-relief region becomes narrower, the center of pressure-relief region tends to transfer to the corresponding center of upper protective layer excavation region, the stress concentration coefficient decreases, the protection angles change little, and the length of the protection region reduces dramatically. (3) e protection region and protection angle calculated based on swelling strain of 3‰ are less than the empirical values based on the dip angle in Provisions, denoting that the method proposed in this study is safer than that in Provisions. e research results provide a useful guide for layouts of roadway and gas drainage boreholes to prevent gas disaster in Nantong coal mine district.

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Solid‐Gas Coupling Model for Coal‐Rock Mass Deformation and Pressure Relief Gas Flow in Protection Layer Mining

Cited by 16 publications

References 7 publications

Numerical Modeling on Hydraulic Fracturing in Coal-Rock Mass for Enhancing Gas Drainage

Numerical Modeling on Hydraulic Fracturing in Coal-Rock Mass for Enhancing Gas Drainage

Optimal Nozzle Structure for an Abrasive Gas Jet for Rock Breakage

Similar Material Simulation Study on Protection Effect of Steeply Inclined Upper Protective Layer Mining with Varying Interlayer Distances

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