Experimental analysis of matrix shrinkage’s influence on mechanical permeability of gas filled coal

Based on the coal seam of Zhao zhuang coal mine and Si he coal mine belong to Jin cheng anthracite Mining Group in Shanxi province, by using the self developed three axial servo controlled seepage equipment for hot fluid solid coupling of coal containing methane, parallel experiments for permeability of helium and methane under different gas pressures are carried out to quantitatively study the influence of Klinkenberg effects on the permeability of coal. Meanwhile, the problem of permeability decreasing caused by fluid pressure decreasing and gas desorption is eliminated by controlling the effective stress. The results show thatthe Klinkenberg effect is obvious under low gas pressure. With the increase of gas pressure, the permeability of coal decreases at first and then increases. The inflection points of gas pressure for Klinkenberg effect are about 0.9 MPa both for coal samples in Zhao zhuang coal mine and Si he coal mine. When the effective stress is constant, with the increase of gas pressure, the permeability increment caused by Klinkenberg effect decreases, while permeability increment caused by coal matrix shrinkage increases. Coal matrix shrinkage has a close relationship with the mechanical properties of coal rock mass. For the coal sample with a poor mechanical property, coal matrix shrinkage is more obvious.     

Mechanism analysis of permeability based on promoting coal matrix shrinkage by water jet

High pressure pulsed water jet (HPWJ) is a new technology of effectively improving coal seam permeability. However, the mechanism of increased permeability is not yet clear, which restricts the application of HPWJ in different coal seams. From the perspective of improving permeability by coal matrix shrinkage, the impelled dynamic equations is established based on analysis of coal dynamic effects by water jet. According to theoretical analysis of the stress state of coal matrix, it is concluded that HPWJ can promote coal matrix shrinkage, and the relationship equation between jet impact-coal matrix is derived. Besides, the gas seepage function in the coal slotted by the HPWJ is gained by using PM model, which provides theoretical support for generalizing the technology in the coal mine.     

Analysis and numerical simulation of fluid-structure coupling of gas drainage from boreholes

Gas drainage from boreholes is main method of utilization and management of Chinese coal seam gas. As the exploitation depth increases, stress field and other factors on the impact of gas seepage are increasingly apparent. Based on the basis of a series of assumptions of coal seam gas, porosity and permeability equations are described by considering stress, coal seam gas pressure change on the coal produced by deformation of the skeleton. The fluid-structure coupling equations are derived by using the basic theorem of porous media flow and the fluid structure coupling theory. The gas seepage field is simulated and analyzed by using multi-physics coupling analysis software. The effect of gas pressure distribution, different burial depths and different drilling parameters (drainage negative pressure, drilling radius) on gas seepage field is obtained. Analysis of simulation results can provide theoretical guidance for on-site gas drainage.     

The application of deep hole pre-split blasting to gas improved extraction in high hydrogen sulphide mine

As the present result of gas extraction by conventional methods in soft low permeability of high-gas mine is not satisfying, deep hole presplitting controlling blasting technology is adopted in Changwu Tingnan coal mine, Shaanxi province. The amount of a single drilling gas extraction increases by 1.36 times, face gas extraction rate edges up to 50% and seam permeability coefficient increases by 9 times. By taking some comprehensive measures, such as enhancing ventilation, drainage, extraction of hydrogen sulfide and lime slurry injection in the blast holes, the hydrogen sulphide is controlled in advanced and the concentration is controlled blow 2×10 -6~4×10 -6, thus the working environment is effectively improved and the safety in production is ensured.     

THE EFFECT OF STRESS ON PERMEABILITY OE COAL AND POROUS ROCK AND FRACTURED ROCK

In this paper, the permeability of coal, porous rock (sandstone), fractured rock(limestone) varifies with different confining pressure is discussed. Exponential functions between permeability and confining pressure are concluded. As a primary exploratiotion of permeability, it is significant to study coal and rock seepage characteristics and methane emission prediction. It is also useful in mine methane drainage system design.     

Pressure Sweep Adsorption Processes for the Concentration of Methane from Coal-bed Gas Extracted

The coal-bed gas was usually extracted from mine in order to avoid coal gas outburst.The Methane(CH4),a main component in coal-bed gas,is a kind of excellent gas fuel and raw material for chemical industry.China is very rich in the resource of coal bed gas,however,most of the coal bed gas extracted from mine is wasted because of the too low concentration of methane. Pressure sweep adsorption(PSA) technique is noticeable among the methods for the concentration of methane from coal-bed gas.However,there are a few studies about this field.Studies on the pressure sweep adsorption(PSA) process for the separation of CH4/N2 using actived carbon as adsorbent are summarized.The thermodynamic relationships and kinetic processes and the influence of the operate parameters on the concentration of methane are investigated.These results have a direct application in coal-bed gas.Some suggestions for the problems need to be solved in PSA process for the separation of methane are also proposed.     

Coal and gas outburst disaster early warning andemergency response decision support technology

In order to realize early warning of coal and gas outbursts, and take timely emergency response, the technology of coal and gas outburst early warning and emergency response decision support is brought forward. The characteristics of abnormal gas outburst are specially analyzed, thus methods are given to monitor and identify the coal and gas outburst disaster. Combined with existing safety monitoring system in the mine, researches of such techniques are carried out as outburst gas content predicting, spread range forecasting and regions of power cutoff. Through those techniques, the Daping coal mine gas explosion disaster is retrieved. In the process of simulation, gas spreading early warning and related emergency response proposals can be issued before the gas arrive.     

The Influence of In-situ Stress Gradient and Geothermal Temperature on The Calculation of Coalbed Gas Pressure

On the basis of coal seam having outcrop of coal seam and outlet on ground,the method for calculating coalbed gas pressure from the one-dimensional stable gas flow equation by considering deeply the influence of in-situ stress gradient and geothermal temperature is presented. In some mine, the theoretically computing and measuring results of coalbed gas pressure show that the in-situ stress gradient and the geothermal temperature have important influence on the calculation of coalbed gas pressure, and if the factors are drew into the calculation of coaled gas pressure,it will make the results much more accurate.     

Numerical simulation of seepage field of gas extraction drilling of single bedding of mining-coal bed

Aiming at the problem of reasonable decorate of coal gas extraction drilling, combining with the initial and boundary condition of borehole extraction, the solid and gas coupling mathematical model of gas seepage of borehole extraction is deduced based on established control equations of seepage field and deformation field. Taking gas extraction of stone coal slit as an example, according to the characteristics of coal seam in the research, the numerical simulation method is used to obtain the distribution rule of gas pressure, coalbed gas permeability, and coalbed gas seepage velocity as well as seam deformation. The effective radius of gas extraction drilling of single bedding about mining-coal bed is determined, which provides the basis for optimum arrangement of gas extraction drilling of single bedding. The results show that the effective radius of stone coal is about 4 m. If the prolonging drilling drainage time is less than 20%, the drilling quantities would reduce by about 50%.     

Triaxial creep model and its stability analysis of gas containing coal 

Investigation on the creep property of coal containing gas is an effective means for understanding the mechanism of delay outburst of coal and gas in a coal mine. This paper conducts triaxial creep tests on the specimens of gas containing coal using a self made creep experimental apparatus to determine the creep law for coal containing gas. An improved triaxial creep model is developed for containing gas by coupling a Nishihara model with another visco elasto plastic body which can describe the deformation property of non Newtonian fluids. The parameter fittings are conducted based on the experimental dada.The present model is examined in terms to the results of triaxial creep tests in various stress level cases. The result shows that the proposed model for gas containing coal can properly represent the creep deformation at different creep stages, especially at the accelerating stage. The instability condition of the model for coal containing gas is also discussed according to stability theories of differential equation solution.     

Numerical Simulation of Strata Movement Behavior in Deep Excavation

According to the complex conditions of deep excavation in Nantong mine, FLAC program are carried out for strata movement, ground pressure and surface displacement due to coal extraction. Based on the analysis of Nantong mine, the basic features of strata movement, the fundamental behavior of ground pressure and the related parameters of surface displacement are obtained. The results are of referential value for mining, supporting and preventing of surface displacement.     

Damage Analysis on Coal and Rocks and the Method of the Checking Damage by the Deviator Stress

The characteristic of the original damage and the breaking of the coal and rocks under the loading has been discussed by a lot of microscopic structure analysis and by whole stress strain testing on the coal and rocks. The non homogeneity causes the stress locating in a small spot. It is the essential cause of the damage developing and causing the structure breaking of the coal rocks. The failure of brittle fracturing, rubbing later on and granulating should be a major pattern in the outburst of coal and gas. The method of the examining damage by the deviator stress, is proposed. It can be used to analyse the characteristic of the coal and rocks.     

Analysis on rock cross-cut coal uncovering using high pressure water jet slotting in close distance seam group

Safe production and procedures at the driving face are restricted in mines of Guizhou province by the long periods required for rock cross-cut coal uncovering in high gas coal seam group. A new method is proposed to solve this problem using high pressure water jet slotting in penetration boreholes. This is proposed to increase the gas desorption rate and reduce drilling hole, which will shorten the cycle of rock cross-cut coal uncovering. Numerical simulation is used to compare the pressure relief effects of different slotting methods in penetration boreholes. The results show that the pressure relief effect of slotting all coal seams is more ideal. Field application indicates that high pressure water jet slotting has good effect of the pressure relief in coal seam group. The drilling number is reduced by 30, the drilling length is shortened by 610 m and the standard time of gas pre-pumping decreases by 39 days.     

Experiments on triaxial mechanical properties of soft coal containing gas

Taking briquette specimens composed by soft coal with outbursting trends as research object, systematic research of the influence on triaxial mechanical properties of soft coal containing gas caused by confining pressure and gas pressure is done. The results show that confining pressure can significantly affect mechanical properties of soft coal containing gas, the compression phase of soft coal containing gas is obvious and the triaxial strength is increased gradually as confining pressure is increased; the influence on elastic modulus and shape of stress-strain curve is not obvious. The triaxial strength of soft coal containing gas shows decrease trend as gas pressure is increased; the influence on strength of soft coal containing gas caused by gas pressure is obvious when the confining pressure is smaller, but it is not obvious when the confining pressure is bigger. the influence caused by gas pressure on elastic modulus and deformation of yield step is not obvious; gas pressure has not only obvious mechanical effects,but also have chemical action on soft coal containing gas; stress-strain curve of soft coal containing gas can be expressed by conic, the influence caused by gas pressure can be considered as equivalent confining pressure effects.     

Study on the Factors Affecting Gas Permeability of Coal

In this paper,the permeability of coal from Nantong colliery is studied in a labo-ratory. The effects of desorbed gas temperature and water content on gas permeability were investi-gated. The results of experiments indieatd that decreasing gas pressure without desorption , the permeability of coal decreases, However, below the desorption pressure, the permeability of coal formethane increases, The reaults suggest that the logarithm of permeability of coal is a linear functionof the temperature and the permeability of coal saturated with water is lass than the permeability ofdry coal; with the increase of water content, the permeability of coal for methane is increasing.     

Engineering Memoir and Features Analysis of Dynamics Phenomena in Yanshitai Mine

The depth of coal mining in Yanshitai mine is over 600 m,dynamics phenomena have been occurred of ter during mining ahd excavating.On the basis of research in Yanshitai mine,this paper recorded the geology and mechanics model of typical dynamics phenomena based on the mining and geology conditions,which have been applied for the mechanism of dynamics phenomena and studied with catastrophe.Meanwhile,the features and influence factor have been studied,and they can be references for mine hazards.     

Study on Adsorption Characteristics of Coal to Gas in Geophysical Field

It is very important to mine safe exploitation, gas drawing and predict of coal and gas outburst that adsorption characteristics of coal to gas in geophysical field are studied. Adsorption and desorption characteristics of coal to gas in geophysical field have been reviewed in detail, then it is obtained that adsorption characteristics of coal to gas in electromagnetic field should be further studied . Adsorption and desorption characteristics of coal to methane in alternating electric field (AEF) have been studied mainly. Adsorption characteristics of three coal samples in AEF have been studied by means of Volume Method. The result shows that chemical properties and matter constituent of coal surface are no changed , adsorption and desorption of the coal samples in AEF well accord with Langmuir equation and two constants empirical formula, and because coal potential energy is increased and coal temperature is raised caused by Joule heat effect , adsorption ability of coal is decreased, and the desorption process is slowed down in AEF.     

Hydraulic Reliability Designing Methods of Gas-Transport Network under High and Medium Pressure

This article analyses the hydraulic reliability of gas -transport network under high andmedium pressure in detail, To increase the hydraulic reliability, it is available to improve the send outpressure in permissible condition.     

Experiment of the gas effect on coal mechanical properties under zero effective confirming pressure

Considering the seal and storage of gas, mechanical index of coal containing gas is usually obtained by normal three-axis experiment. While, according to national standard, mechanical index of coal is usually tested by uniaxial experiment. By utilizing the gas sealing system, an analogic uniaxial experiment method is proposed. Through designed experiments, the effect of gas on mechanical properties and mechanical response of the coal sample when effective confirming pressure is 0 is studied too. The experimental results show that pore gas changes the mechanical response of complete deformation stage, but the trend of change gradually weakens as the gas pressure increases, and it means that non-mechanical effects caused by absorbed gas play a leading role gradually.     

The influence of initial internal structure of coal sample on gas flow characteristic

Three kinds of coal samples with different components are chosen as study objects.Density calculation and SEM are adopted to study their internal structures,and a self made triaxial gas seepage instrument is used to study their internal gas flow characteristics.The results show that internal structures of coal samples made of different particle size coal powders under identical external conditions are various,and nonlinearity is presented on the influence caused by fabric.Gas flow characteristic is complex in complete stress strain process,generally it firstly increases and then decreases,initial gas flow velocity is lower than the one after the failure of coal sample,and obvious hysteretic nature of gas flow characteristic is showed.The influence of gas flow characteristic caused by initial internal structure of coal sample is nonlinear and the stress sensitivity is high on the influence of gas flow characteristic caused by initial internal structure.The more complex the initial internal structure of the coal sample is,the lower the axial tress sensitivity is,and the higher the confining pressure sensitivity is.