Coal Seam Water Infusion Research Articles

Experimental Study on Coal and Gas Outburst Risk under Different Water Content Rates in Strong Outburst Coal Seams.

To investigate the alleviation potency of coal seam water infusion on coal and gas outburst, this paper focuses on the Qidong coal mine outburst coal seam, where outburst accidents have occurred many times, and obtains the impact of water content on outburst prediction parameters by studying the features of outburst parameters and gas desorption law under different water content rates. How water content affects outburst was also researched through the use of a self-made outburst simulation test system, and the relationship between water content and outburst intensity and critical gas pressure was studied. It can be concluded that with the rise of water content, the initial velocity of gas diffusion, the gas desorption index of drilling cuttings, and the adsorption constant a decrease, but the firmness coefficient (f) increase, and these indicators are exponentially related to the water content. Meanwhile, as the water content raises, the outburst pressure threshold increases, the outburst intensity gradually decreases, and the less likely outburst occurs. Under 0.5 MPa pressure, as the water content arose from 2.02 to 5.14%, the outburst intensity was significantly weakened, while no outburst occurred as the water content reached to 10.25%. Fitting analysis of the influence curve of outburst parameters and comparing the vital values of outburst prediction indexes finally determined that the water content rate of 5.14% could be used as a key index for water injection measures for coal and gas outburst prevention coal seam in Qidong coal mine no. 9. This research offers a guiding significance for the outburst prevention measures of water infusion in outburst coal seams and gives a feasible scheme for the safe mining of outburst coal mines.

Development and application of a new compound wetting agent for coal seam water infusion

To improve the dust-suppression effect of water infusion in coal seams, a compound wetting agent was developed as a water infusion additive by using the synergistic effect between various surfactants and surfactant compounding with inorganic salts. Firstly, single factor experiments were conducted to select three surfactants with good wettability from nine surfactants by taking surface tension and contact angle as research objects. Then, the critical micelle concentration (CMC) of surfactants was selected as the concentration of the compound solution and the three selected surfactants and two inorganic salts were then mixed. The optimum ratio of the new compound wetting agent is 0.1% wt% rapid infiltration T +0.1 wt% OA-12% +0.1 wt% NaCl by comparing the surface tension and contact angle of various compounds in solution. Finally, the wettability of the compound wetting agent was obtained by coal dust settling and low-field nuclear magnetic resonance (L-FNMR) experiments. The results imply that the compound wetting agent can significantly improve the coal dust settling velocity to 18.38 mg/s, and increase the wetting rate of coal pore water. The test indicates that the new compound wetting agent can improve the dust removal efficacy of water infusion. The average water content increment in a water-infused coal seam with the new compound wetting agent is about 2.33%, and the dust reduction rates of total dust and respirable dust are increased from 63.6% and 67.5% to 89.2% and 91.6%, respectively. The new compound wetting agent exerts significant dust reduction effect on the N1105 fully mechanized coal mining face in the Yuwu Coal Mine.

Effect of Sodium Dodecylbenzene Sulfonate on the Wetting Mechanism of Tunliu Coal

AbstractCoal dust in the coal mining process may lead to a serious threat to the safety and health of miners. The addition of surfactants during coal seam water infusion can significantly improve the effect of dust suppression, so it is crucial to study the influence mechanism of surfactants on coal wettability. The variation of the hydration film thickness on the Tunliu coal surface at different concentrations of sodium dodecylbenzene sulfonate (SDBS) solution was investigated by atomic force microscopy. The experimental results indicate that the hydration film thickness increases initially and decreases afterward with the SDBS solution concentration increase, with a maximum value of 11.4 nm. The surface free energy (SFE) of coal molecules adsorbed with different numbers of SDBS molecules were calculated using two coal molecule cell models developed by Materials studio 8.0, and the simulation results display a good agreement with the experiments. The higher the SFE, the greater the hydration film thickness on the coal surface, and the stronger the enhancement effect of SDBS solution on the wettability of coal at the corresponding concentration. The interface formation energy (IFE) and cohesive energy density (CED) of coal molecules after adsorption of SDBS molecules were calculated separately. It was found that when three SDBS molecules were adsorbed, the absolute value of IFE and CED reached the maximum, and each SDBS molecule had the strongest average effect on coal molecules, the bond between them would be tighter. SFE simulations are helpful to optimize the selection of surfactants for practical engineering applications.

STUDY ON THE DYNAMIC EVOLUTION LAW OF THE EFFECTIVE STRESS IN THE COAL SEAM WATER INFUSION PROCESS BASED ON FRACTAL THEORY

The effect of the coal seam water infusion to reduce dust is directly related to the development degree of the coal structure under the action of the effective stress. Therefore, this paper first summarizes several basic effective-stress models and proposes the effective-stress model considering the capillary force. Thereafter, the nuclear magnetic resonance (NMR) experiment system high-voltage seepage module is used to achieve the saturation coal sample T[Formula: see text] and water infusion coal sample T2test under different mechanical environments. And the fractal dimension was calculated based on the results of porosity and pore size test. Finally, the parameters were sequentially substituted into effective-stress models. The calculation results were compared and analyzed. The results show that the saturation levels of the irreducible fluid of Sample DLT and Sample XLZ are 92.93% and 93.66%, respectively, indicating that these samples are dense porous media structures. Meanwhile, the porosity test shows the overall porosity with the water infusion pressure and confining pressure changes being consistent with the conventional law; the partial porosity caused a slight fluctuation due to different sensitivities of different pores to stress. The effective stresses of the capillary force and the calculated effective stress of the body are closest to the fractal effective stress, so the difference between the two values is negligible due to the small capillary force, which indicates that during the high-pressure water infusion, the capillary force in the meso-structure hardly affects the mechanical environment. Based on the theoretical research results, this paper can provide a theoretical reference for the determination of water infusion parameters under different on-site mechanical environment during the process of coal seam water infusion, which is conducive to the popularization and application of this technology, thus, providing the scientific basis for safe mining of the deep coal seam and ensuring the safe and efficient production of mines.

Experimental study on spontaneous imbibition characteristics of coal based on fractal theory

Coal seam water injection is a widely used dust reduction technology in Chinese coal mines. During the process of coal seam water injection, a large amount of broken coal particles will accumulate in the pore, which will affect the flow characteristics of water. It's very important for improving the on-site coal seam water injection and dust reduction technology to study the influence of coal particles on the water migration law. In this paper, a spontaneous upward imbibition experiment was used to study the effect of coal particles stacked in front fractures on water migration in coal seam water infusion. Then, a mathematical model was established to express imbibition speed and stable imbibition height. The results show when the largest particle size is selected, theoretical calculation results of stable imbibition height is closest to the experimental data; coal particles with a size of 564–1589 μm have the greatest influence on the wetting phase of coal seam water infusion; the metamorphic grade and particle size of the samples mainly affect the initial stage of water migration, and the initial imbibition speed of each coal sample is quite different. However, with increasing imbibition height, the imbibition speed difference of each coal sample gradually decreases.

Coal seam water infusion for dust control: a technical review.

Coal mine dust continues to be a health and safety issue in underground coal mines. Coal seam water infusion was developed and widely applied in European coal mines for dust control, and was also a common practice in most Chinese coal mines. This method typically involves the infusion of water into the coal seam to increase its moisture content, and therefore reduce dust generation during mining operations. With the availability of other dust control methods such as water spraying systems, the water infusion method has not been considered as a viable means for dust mitigation in modern mines. However, the increase in production output and the deployment of more powerful equipment for coal cutting and transport and intensive gas drainage practices mean that workers could be exposed to more dust contaminations. Whilst the mine operators are committed to suppress and dilute airborne dust particles using these passive measures, there is a need to critically examine and subsequently develop this proactive dust control technology for practical applications in Chinese coal mines. The paper provides a critical review of the water infusion technologies in view of its technological advances and practical application limitations. The methods of water infusion, mechanism of water flow in coal, the role of surfactants and the key parameters influencing the effect of water infusion on dust control are identified and discussed. Existing problems and prospects for water infusion are analysed.

Experimental Study on the Pore Structure Fractals and Seepage Characteristics of a Coal Sample Around a Borehole in Coal Seam Water Infusion

Coal seam water infusion is a universal comprehensive mine disaster prevention method practiced worldwide. The result of water infusion is determined by the structure and seepage characteristics of the coal sample around the borehole. In this paper, the structure and seepage characteristics of the coal sample under various stress and pore water pressures are measured via nuclear magnetic resonance (NMR) technology; the influence rule of confining pressure and pore water pressure during the test on the coal sample structure and seepage characteristics is analyzed. Based on fractal geometrical theory, the fractal model of permeability is created. The results show that the coal sample with water infusion has an intertwined internal fracture-pore structure and that the pore radius distribution is diverse. Through theoretical analysis and discussion, we found that there are no large changes in the pore area fractal dimension and the measured pore volume fractal dimension, but the trends of changes in these two fractal dimensions are opposite, because the pore area fractal dimension characterizes the homogeneity of the pore area distribution on the surface of a coal sample, and the measured pore volume fractal dimension characterizes the cumulative volumetric changes in the pores inside a coal sample. The changes in these two fractal dimensions validate that the pore structures inside a coal sample have similar in fractal characteristics and demonstrate that the coal seam water infusion technique will not damage the skeleton of the coal sample. The variation rules of theoretical permeability from the fractal model and the value from the liquid measurement versus confining pressure and pore water pressure are consistent, an increase in the water pressure will result in an increase in the permeability, and an increase in the confining pressure will result in a decrease in the permeability. However, because the seepage channels with a large diameter in the tested coal sample were blocked, there is a relatively large difference between the two permeabilities. Therefore, increasing the connectivity between the seepage channels with a large diameter will improve the effects of water infusion, which is implemented to prevent disasters. Through NMR experiment and theoretical analysis, this study establishes a quantitative relationship between the pore structures inside the coal sample and its permeability during coal seam water infusion process, provides an advanced experimental approach and theoretical analysis method, which will be of great importance in the improvement in the water infusion process implemented in deep working coal seams to prevent disasters and in the determination of the range of application of this process and the evaluation metrics for this process.

Preparation of a New Borehole Sealing Material of Coal Seam Water Infusion

To improve the borehole sealing effect of coal seam water infusion, especially that of coal seam with low permeability and high rigidity, this study investigated the performance test optimization of two cement‐based sealing materials. The borehole sealing effect of this coal seam requires high‐pressure water infusion. Result shows that when the water‐cement ratio is 0.4 and the amount of fiber expansive agent is 10%, the new borehole sealing material displays microexpansion. In addition, the 1‐day compressive strength reaches 16 MPa. This result satisfies the material compressive strength requirement under 30 MPa high‐pressure water infusion. The sealing performance is also excellent. According to the scanning electron microscopy analysis of new borehole and traditional borehole sealing materials, the surface of new borehole sealing material shows no holes and possesses compactness. The sealing effect is superior to that of other traditional sealing materials. This effect can satisfy the sealing requirement of coal seam water infusion. The new borehole sealing material is considerably significant for the improvement of the water infusion effect.

Effect of Saturation Time on the Coal Burst Liability Indexes and Its Application for Rock Burst Mitigation

Coal seam water infusion is one of the widely used techniques for rock burst mitigation, and the saturation time of coal is one of the essential factors influencing the effectiveness of water infusion. To analyze the effect of saturation time on coal burst liability indexes, bursting liability indexes of coal specimens taken from No. 2 mining face in Changgouyu Mine in Beijing were tested under natural state and different saturation time. Compared with coal specimens under natural state, the uniaxial compressive strength, elastic strain energy index, and bursting energy index all decrease in different degrees as the saturation time increases. The dynamic failure duration, however, shows an opposite tendency. When the saturation time is 0–6 days, the bursting liability indexes vary significantly, but when the saturation time is longer than 6 days, this phenomenon is not very obvious. When the saturation time increases from 0 to 6 days, the uniaxial compressive strength, elastic strain energy index, and bursting energy index decreases from 18.31 to 7.15 MPa, 2.59 to 1.25, 3.04 to 1.20, respectively, but when the saturation time increases from 6 to 8 days, their corresponding increments are only 0.02–0.05. Moreover, the time of coal seam water infusion in No. 2 mining face was designed 6–8 days based on the test results. Practical experiences show that excellent destress effect was achieved by water infusion. After coal seam water infusion, the average moisture content of coal seam increases from 0.85 to 1.26%, and the width of destress zone increases from 0–4 to 0–6 m.

Study on Water Seepage Law of Raw Coal During Loading Process

In order to reveal the water seepage law of raw coal during different loading process, the gravity constant load seepage experimental system is developed and used in this paper. The water seepage law of raw coal during different loading process was tested. The mathematical model of axial strain-damage-permeability coefficient during the loading process is proposed based on the Wei-bull distribution of coal damage. According to the water seepage experiments and results analysis, the following conclusions are gotten. Under the same experimental conditions, with the increasing of axial pressure, the permeability coefficient of coal sample has a distinct decrease trend, and then an increase trend when reached the extreme point. The same trend of permeability coefficient-strain curves and stress-strain curve of the raw coal samples under different axial pressure are got-ten, that mean the permeability coefficient is closely related to the damage evolution process. The water seepage law of raw coal during different loading process can be described by the mathematical model of axial strain-damage-permeability coefficient, and its parameters can be obtained easily. This research is important for revealing the mechanism of coal seam water seepage, guiding field coal seam water infusion, controlling mine water hazard, preventing coal mine disasters.

The Selection and Application of a Compound Wetting Agent to the Coal Seam Water Infusion for Dust Control

ABSTRACTCoal mine dust may lead to coal miners’ pneumoconiosis and dust explosions, thus being seriously harmful to human beings. A wetting agent is commonly used to improve the efficiency of water infusion for mine dust control. Therefore, selecting an optimal wetting agent is crucial to this practice. This study measured surface tensions, contact angles, and capillary imbibitions of the wetting agents lauryl sodium sulfate (SDS), sodium dodecyl benzene sulfonate (LAS), sodium dioctyl sulfosuccinate (AOT), and SDS compounded with five additives on a coal-seam sample in the laboratory. Their wettability is comparatively investigated. Results indicate the following: (1) to select an optimal compound wetting agent, it is necessary to calculate a capillary force rising factor or to conduct capillary imbibition tests besides the measurements for surface tension and contact angle; (2) a compound wetting agent made of 0.10 wt% SDS + 0.05 wt% NaAc is optimal for the wettability enhancement of this coal. Its capillary force rising factor is 1.44 and its capillary imbibition rate is 2.96 times that of water without wetting agent. Field test results also confirmed that adding the optimal compound wetting agent into water infusion can significantly improve dust-prevention efficiency.

Fuzzy Clustering Analysis and Application of the Degree of Difficulty of Coal Seam Water Injection

The degree of difficulty of coal seam water infusion is the important basis of pouring water into coal beds, by fully analyzing influence factors of the degree of difficulty of pouring water into coal beds, the main influence factors of pouring water into coal beds was determined and the fuzzy clustering analysis model was build which base on the depth of burying of the coal seam, crack growth degree, porosity, moist edge, water saturation value-added and consistent coefficient. By comparing evaluation result of this model with Fisher evaluation result, the model result is accuracy and reliability. According to this model to predict South decurrent 18th layer 7th face Coal Seam of Shuangyashan Mining Group Dongrong No.2 Coal Mine,the predicted results are consistent with the actual situation and offering theoretical guidance to the choice of injection water parameters .

Application of Power Ultrasound in Coal Seam Water Infusion

The infusion increase mechanism of power ultrasound on coal seam water infusion and its prospect of application are introduced. The research results show that: the main mechanism of power ultrasound to coal and water are mechanics and cavitations function. The porosity and permeability of coal can be improved due to the power ultrasound, so the speed of the water into the coal is improved. The technology of power ultrasound on the coal seam water infusion has a good application prospect.

Research and practice on fluctuation water injection technology at low permeability coal seam

In order to solve the problem of poor affusion effect on low permeability coal seam, the paper analyzes the micro process of the coal seam water infusion in wetting coal and determines the main factors affecting coal seam water infusion. The permeability of the NO.3 coal seam in east working face of Xingcun coal mine by MTS815.03 servo-controlled rock mechanical test system has been tested. Results show that when the peak stress in coal sample specimens reaches 48.53MPa, permeability ranges from 0.5158 to 2.9576×10−8Darcy, and it means that the coal seam is low in permeability and difficult in water injection. Based on the characteristics of low permeability and geostress situation, efficient fluctuation water injection technology with permeable agent and relevant process parameters have been designed. The surface tension of the permeable agent developed here is 31.18mN/m when mass concentration reaches 0.05%. The permeable agent can permeate into 2cm thick coal layer completely in 10s, thus improving the wettability of water effectively and the water injection pressure fluctuates between 7MPa and 25MPa. The application of the technique in the 3rd coal seam in east working face of Xingcun coal mine shows not only single-arch injection experienced a significant increase on average, from no more than 10m3 to 63.3886m3, but also the effect of dust fall, cooling and rock burst prevention is remarkable.

Experimental Study on Inhibitory Effect of Gas Desorption by Injecting Water into Coal-sample

Abstract In order to further study inhibitory effect of gas desorption in coal seam water infusion, the laboratory test method is used in this paper, which experiments on coal sample that is fully adsorbed methane before being injected water into. By the experiments, gas desorption isotherms, gas desorption rate and residual gas content after water injection are obtained. And also, the following test results are got: the first, with water being injected, coal gas desorption isotherms moves upward, that is, gas content in coal sample increases under a certain balance pressure; the second, with water being injected, it can lower both the initial desorption rate and the attenuation speed of gas adsorption in coal sample, that is, coal gas desorption rate curve becomes more smooth; the third, with water being injected, it increases residual gas content in coal, and residual gas content increases with injection pressure and water content. Through these experiments, the following conclusions can be drawn: with high pressure water being injected into pores of coal, residual water in coal has inhibitory effect to adsorption methane, ultimately, reducing gas desorption rate and desorption volume; so that, water injection is benefit for gas outburst, and the inhibitory effect is an important role in mechanism of water injection to prevent coal and gas outburst.

Application of affusion in Coal for Dust Control

The situation of infusion in coal seam technology at home and abroad, the effect of dust control for every aspect in mining, and the mechanism of coal seam water infusion in micro and macro have been described in detail. The influence of capillary and molecular diffusion movement in coal group should be noticed. Combined with the practice of light-weight top coal caving mining in local and analysis on the technology of infusion in seam, some detail research on the effect of decreasing dust has been done. The control of water infusion quantity, drilling spacing and the length of hole sealing have got appropriate data for further research. The appropriate parameters of water infusion process provide basis for the following research and production.