Coal Seam Gas Content Research Articles

Research on an Equivalent Algorithm for Predicting Gas Content in Deep Coal Seams

This document introduces a novel equivalent algorithm for forecasting gas content within deep coal seams, which is subject to constraints stemming from the advancements and precision achieved in well and roadway engineering endeavors. This algorithm meticulously acknowledges that coal seam gas content comprises three fundamental components: the inherent gas emission rate of the equivalent stratum, the residual gas content retained within the coal seam itself, and the influence imparted by the gas content within the coal seam. Furthermore, the approach thoroughly considers variations in the level of porosity development within the coal seam and its surrounding rock formations, as well as the occurrence of gas within these structures. The equivalent layer is classified into two distinct groups: the sandstone zone and the clay zone. The sandstone zone utilizes pertinent parameters pertaining to fine sandstone, whereas the clay zone distinguishes between clay rock and thick mudstone. The influencing factor considerations solely encompass natural elements, such as the coal seam’s occurrence and geological structure. The residual gas content employs either existing measured parameters or acknowledged experimental parameters specific to the coal seam. Based on this predictive approach, an intelligent auxiliary software (V1.0) for mine gas forecasting was devised. The software calculates the gas content of deep coal seams within the mine at intervals of 100 m × 100 m, subsequently fitting the contour lines of gas content across the entire area. The gas content predictions derived from this equivalent algorithm demonstrate robust adaptability to variations in gas content caused by construction activities, and the prediction results exhibit an acceptable level of error on-site. Notably, the prediction process is not constrained by the progress of tunnel engineering, ensuring that the prediction outcomes can accurately represent the distribution characteristics of deep coal seam gas content. After a year of application, the prediction results have consistently met on-site requirements, providing a scientific foundation for the implementation of effective gas prevention and control measures in the mining area. Furthermore, this approach can effectively guide the formulation of medium- and long-term gas prevention and control plans for mines.

Modelling of enhanced gas extraction in low permeability coal seam by controllable shock wave fracturing

The controlled shock wave (CSW) fracturing is an effective method for enhancing permeability of coal seam to promote gas extraction. Based on Fick’s law, Darcy’s law, the ideal gas law and the Langmuir equation, a damage-seepage-deformation coupling mathematical model of CSW fracturing in coal seam combined with the maximum tensile stress and the Mohr-Coulomb criterion is established. This model is implemented into COMSOL Multiphysics to simulate the coal seam CSW fracturing and subsequent gas extraction. When the shock wave and isotropic in-situ stress are applied on the borehole wall, the coal damage zone is an annular shape, and the permeability in the damage zone increases sharply. The CSW can effectively increase the efficiency of gas extraction and reduce the gas pressure and gas content in coal seam. With the increase of CSW action times, the damage in coal mass reaches a threshold and tends to be stable after several shocks. The damage area and the gas extraction efficiency are positively correlated with the shock intensity. Under the anisotropic ground stress, the larger diversity of the stress in different directions is, the more obvious damage extension in the fractured coal along the maximum stress direction is. Ground stress can inhibit the extension of cracks in the CSW fractured coal seam. This inhibition effect becomes more obvious with the increase of in-situ stress. Parameters are substantiated of controlled shock wave impact on the coal seam, which ensures increased methane extraction from low-permeability reservoirs, are substantiated.

Study on the Spontaneous Combustion Law of Coal Body around a Borehole Induced by Pre-extraction of Coalbed Methane.

To address the challenges associated with the high gas content, high pressure, and low permeability coefficient in deep coal seams, strategies such as infilling boreholes and increasing the negative pressure of extraction are commonly implemented to alleviate issues related to coalbed methane extraction. However, long-term mining pressure can lead to the development of cracks in the coal seam near the borehole, thereby creating air leakage channels, which could potentially impact the oxygen supply during the extraction process. This leads to secondary disasters such as the spontaneous combustion of coal and gas explosions, considerably impacting the life and health of underground workers. To solve this issue, a thermal-fluid-solid coupling model for the working surface was constructed based on numerical simulation software, taking into account the multimechanism coupling effect of coal seam gas. The laws of coal oxidation and spontaneous combustion induced by coalbed methane extraction around boreholes were studied. The variation laws of the oxygen concentration, coal temperature, and oxidation heating zone around the borehole under different extraction conditions were simulated and analyzed. The findings demonstrate that the negative extraction pressure enables the gas to penetrate the fracture zone of the borehole, leading to an increase in the oxygen consumption rate and coal temperature around the borehole with an increase in negative extraction pressure. The coal gas leakage surrounding the borehole reduces as the sealing depth increases, and both the heating rate of coal and oxygen volume fraction show a downward trend. The fitting relationship between the negative pressure of drainage, depth of sealing, and temperature change in the coal body surrounding the boreholes was identified. It was determined that the negative pressure of 13 kPa for borehole drainage and a sealing depth >18 m are the optimal extraction parameters. The range of the oxidation zone and the position of the boundary line under this parameter were predicted, and the position function of the dangerous area of oxidation heating was defined. The research results have remarkable implications for the coordinated prevention and control of gas and coal spontaneous combustion in coalbed methane predrainage boreholes, as well as for efficient prevention and control of CO in on-site gas extraction boreholes, thus ensuring efficient and safe gas extraction.

Heat-dependent properties of methane diffusion in coal: an experimental study and mechanistic analysis.

Coalbed methane thermodynamic extraction, as an emerging ECBM recovery method, can effectively improve gas recovery rates. And clarifying methane diffusion and migration law in coal under thermal stimulation is crucial for the selection of its process parameters. Based on laboratory methane adsorption-release experiments, the evolution law of methane diffusion characteristics with temperature and pressure was studied, and the control mechanism of heat-dependent methane diffusion behavior was explored. The results show that both thermal stimulation and high adsorption pressure accelerated the methane diffusion rate in coal. Adsorption pressure had little effect on methane diffusion percentage, but thermal stimulation promoted a significant increase in diffusion percentage and improved the net methane yield. The influence mechanisms of adsorption pressure and thermal stimulation on methane diffusion characteristics are elucidated in relation to the amount and proportion of methane-activated molecules in the diffusion process. The constant diffusion coefficient of methane is heat-dependent, based on which a diffusion model is derived to accurately predict the methane release process in coal. Additionally, temperature has a more important effect on transient diffusion coefficient than pressure. Thermal stimulation leads to a net increase rather than a decrease in diffusion coefficient in the early diffusion stages and can also accelerate the attenuation of diffusion coefficient, with this intensifying effect becoming more pronounced at higher temperatures. The research results can provide some reference for the determination of coal seam gas content and the selection of heat injection process parameters.

Prediction model of coal seam gas content based on kernel principal component analysis and IDBO-DHKELM

Abstract Accurate coal seam gas content assists in the effective prevention of coal and gas outburst accidents. To solve this problem, an IDBO-DHKELM coal seam gas content prediction model is proposed by combining improved Dung Beetle optimization algorithm (IDBO) with a deep hybrid kernel extreme learning machine (DHKELM). First, the index factors of the coupled gas content are determined according to the influence factors of coal seam gas content and the actual situation of mine production. The correlation of index factors is analyzed by SPSS 27 software via Pearson correlation coefficient matrix. Then, the principal components of the original data are extracted using the principal component analysis method (KPCA). Second, sine chaotic mapping, fusion improved sinusoidal algorithm, and fusion adaptive Gauss–Cauchy hybrid mutation perturbation are introduced to improve the Dung Beetle optimization algorithm (DBO) to enhance its global search capability. Third, IDBO is used to optimize the number of hidden layer nodes, regularization coefficient, penalty coefficient, and kernel parameter in DHKELM, which improves the prediction accuracy and further avoid the phenomenon of overfitting. Finally, the principal component extracted by KPCA is taken as the model’s input, and the gas content as the model’s output. The results are compared and analyzed with those of PSO-BPNN, GA-BPNN, PSO-SVM, and DPO-DHKELM models. The results demonstrate that the IDBO-DHKELM model’s performance is the best in each performance index. Compared with other models, the mean absolute error of test samples in the IDBO-DHKELM model is reduced by 0.402, 0.4407, 0.3554, and 0.0646, respectively. The mean absolute percentage error is decreased by 3.67%, 4.07%, 8.27%, and 6.35%, respectively. The root mean square error decreased by 0.7861, 0.7148, 0.3384, and 0.1186, respectively. The coefficient of determination (R 2) is increased by 0.1544, 0.1404, 0.0955, and 0.0396, respectively. Finally, the IDBO-DHKELM model and other models are applied to an experimental mine. The resulting IDBO-DHKELM model is the closest to the actual value, which further verifies the universality and reliability of the model. Therefore, the model is more suitable for the prediction of coal seam gas content.

Investigation into the variation characteristics and influencing factors of coalbed methane gas content in deep coal seams

Gas saturation is a critical parameter for the selection and development of coalbed methane, as well as a key indicator reflecting the challenges in coalbed methane development and productivity evaluation of coalbed methane wells. As one of the significant factors influencing gas saturation, gas content plays a vital role in comprehensively investigating coal pore properties to fully comprehend the process and conditions of methane adsorption and desorption. In this study, 3# and 15# coals from Qinshui Basin, China was selected as research subjects. The experimental evaluation encompassed an examination of composition, pore characteristics, permeability characteristics of coal, rock mechanical parameters while discussing the impact of temperature and pressure on coal's adsorption and desorption capacity. The mineral characteristics analysis revealed that vitrinite is the main component with varying percentages and reflectance values in both 3# and 15# coal seams. The gas content and methane concentration in the 15# coal seam are higher than those in the 3# coal seam. The relationship between gas content within a coal seam and burial depth depends on achieving a balance between positive pressure effects caused by overburden stress exertion on gases trapped within pores under high pressures during burial history versus negative temperature effects due to cooling during geological processes over time. Predictions were made regarding deep-coal gas content which holds significant implications for accurately understanding variations in desorption behavior along with optimizing fracturing engineering.

Characterizing coal gas reservoirs: A multiparametric evaluation based on geological and geophysical methods

The gas content of coal seams is a key parameter to guide the development of coalbed methane (CBM). While most studies focused on geological features, geophysical methods provide a powerful tool for the analysis of the differential distribution of CBM. In this paper, we present a comprehensive model for the quantitative evaluation of gas content in coal seams based on the computation of multiple parameters including lithology coefficient, deformation coefficient, and ash content. Based on the results of industrial analysis and isothermal adsorption tests of 135 coal samples, logging data of 76 CBM wells, as well as 10 2D seismic lines, a geophysical evaluation method of lithology inversion, structural curvature calculation, and ash content identification was established. Our study reveals the differential distribution characteristics of gas content in coal seams under the coupling effect of the three parameters. The results from this method were applied in the southeastern margin area of the Ordos Basin where 5# coal seam with sandstone and mudstone is interbedded as the roof and floor, and the mudstone in the roof contributes more to the sealing ability of surrounding rock. For the 8# coal seam with stabilized limestone and thinly interbedded mudstones as the roof, the limestone contributes most to the sealing ability. The sealing ability of surrounding rock is poorer in the area with large sandstone content in the roof and floor of coal seams and large structural curvature. The lithological combination of the 5# coal seam is the most critical gas controlling factor, whereas deformation coefficient is found to be least significant. However, for the 8# coal seam with little change in the lithology of the roof, the effect of deformation coefficient on gas content increases, and the adsorption capacity is the most important factor influencing the differential distribution of CBM.

Density and volume of adsorbed methane in key applications for in-situ gas content: Insights from molecular simulation

The evaluation of the in-situ gas content in deep coal seams, potentially containing free gas in saturated-oversaturated reservoirs, holds practical significance for exploration and production compared with shallow undersaturated-saturated reservoirs dominated by adsorbed gas. However, owing to the inherent limitations of volumetric and gravimetric methods, the accurate assessment of adsorbed and free gases faces significant challenges. In this study, based on molecular simulations, we focused on slit-shaped pores to explore the microscopic interaction mechanisms between coal and methane molecules under different pore sizes, temperatures, and pressures. By combining isothermal adsorption and pore structure experiments, the distribution characteristics of the adsorbed phase density (APD) and adsorbed phase volume (APV) were determined. The results showed that, in pores smaller than 1.5 nm, methane exhibited an aggregated state distribution (containing only adsorbed methane) characterized by micropore filling adsorption. In pores larger than 1.5 nm, methane showed a dispersed state distribution (coexistence of adsorbed and free methane) characterized by monolayer adsorption. The APD increased with pressure and decreased with temperature and pore size, whereas the APV remained independent of the pressure and temperature. In the in-situ gas content evaluation, three adsorption models (SL, SDR, and SL + SDR models) considering APV and APD were utilized to describe the methane adsorption behavior. The SDR model considering the APV was consistent with the actual physical properties and molecular simulation results. Traditional correction methods often lead to an overestimation of the adsorbed methane content, and neglecting the APV can result in an overestimation of the free methane content. In summary, the SDR model considering the APV can provide more rigorous scientific support for the refined study of methane occurrence states and gas content distribution.

Использование биологических рабочих агентов для снижения углеродного следа

Introduction. Chemical compounds related to greenhouse gases (CO2, CH4, N2O, some fluorinated F-gases), capturing the energy of the Sun and absorbing infrared radiation, create a greenhouse effect above the Earth’s surface. In order to assess the impact of humanity on the climate system, the carbon footprint indicator is used, which takes into account greenhouse gas emissions from anthropogenic human activities. This indicator is used to estimate direct emissions from technological processes that can be controlled and from indirect emissions that occur during the product lifecycle. One of the promising areas for reducing greenhouse gases can be considered the use of biological working agents. The purpose of the research. Conducting an assessment of the possibilities of using biological working agents to reduce the carbon footprint in mining enterprises. Methodology. The research was conducted on the basis of analyses of literary data from Russian and foreign sources, specific preventive and compensatory initiatives for the absorption of greenhouse gases from the atmosphere based on the participation of biological working agents were considered. Results and discussion. As a result of the research, various technologies for reducing the carbon footprint using biological working agents were considered. Dependences of the carbon footprint on changes in the natural gas content of coal seams for coalmines were obtained. The carbon footprint was calculated when obtaining energy resources for the extraction of 1 ton of coal using various types of fuels, during the burning of rock dumps. It is proposed to use biological working agents to reduce the carbon footprint using various technologies to reduce direct and indirect emissions, as well as to recycle greenhouse gases to obtain alternative energy. The results of the study of the applicability of biological working agents in mining enterprises in order to reduce the carbon footprint are shown. Conclusions. 1. Research has been conducted on the use of various technologies to reduce the carbon footprint using biological working agents in relation to mining enterprises. 2. It has been determined that biological working agents, when used in mining enterprises, can reduce the carbon footprint from direct greenhouse gas emissions by many times, as well as deposit carbon for many years by extracting CO2 and other gases directly from the air, growing trees and plants with high biological productivity capable of sequestering carbon dioxide. 3. It has been found, that biological working agents are able to process CO2 to produce various useful products, as well as utilize greenhouse gases to produce alternative energy.

Desorption Characteristics of CH4-C2H6 Mixed Gas in Heavy Hydrocarbon-Rich Coal Seams.

The gas desorption characteristics of coal are closely related to the gas content of the coal seam. The gas in heavy hydrocarbon-rich coal seams contains CH4 and C2H6 heavy hydrocarbons. However, most current research on the gas desorption characteristics of coal seams focuses on CH4 analysis, ignoring the influence of the C2H6 heavy hydrocarbon gas. To accurately determine the gas content of a heavy hydrocarbon-rich coal seam, methods based on CH4 analysis are inadequate and the desorption characteristics of CH4-C2H6 mixed gas must be clarified. This work experimentally and theoretically studies the desorption characteristics of single-component gas and CH4-C2H6 mixed gas from coal samples. The results show that increasing the adsorption-equilibrium pressure was found to increase the desorption quantity and desorption speed of single-component gas and increase the desorption quantity, desorption ratio, and diffusion coefficient of mixed gas. Under the same adsorption-equilibrium pressure, the desorption quantity and rate of single-component CH4 gas exceeded those of C2H6. The quantity and speed of mixed gas desorption increased with rising CH4 concentration and decreased with rising C2H6 concentration. The change in the mixed gas concentration during desorption reflects the distribution characteristics of light hydrocarbon components on the outer surface and heavy hydrocarbon components on the inner surface of coal. From the desorption characteristics of mixed gas, desorption models of mixed gas were obtained at different concentrations, laying a theoretical foundation for accurate determinations of gas contents in heavy hydrocarbon-rich coal seams.

Re-cognition of adsorption phase density and adsorption phase volume: Insights from methane adsorption behavior

The determination of adsorption phase density significantly influences the assessment of gas occurrence state and gas content within in-situ reservoirs, particularly for the evaluation of gas content in deep coalbed reservoirs. Despite the extensive research on adsorption phase density, various calculation methods encounter limitations due to the inability to directly measure it. Simultaneously, the considerable disparity in results obtained from various adsorption phase density methods hampers the accurate determination of adsorbed gas and free gas content in deep coal seams. To address these challenges, this study systematically reviews calculation methods and highlights issues related to adsorption phase density. Considering practical experimental conditions, two new calculation methods are proposed: the adsorption potential adsorption phase density (APD) method and limit adsorption phase density (LAD) method. These methods enable the directional calculation of adsorption phase density based on the unknown or known absolute adsorption amount. The obtained results reveal that the adsorption phase density obtained through the APD method exhibits variations in temperature and pressure. For different coal rank samples, the range of actual adsorption phase density at different temperatures under high pressures is expected to fall between 0.30 g/cm3 and 0.40 g/cm3. The range can serve as a theoretical upper limit value for refining adsorption phased density models. The adsorption phase density acquired through the LAD method exhibits variations in temperature and pressure, whereas the adsorption phase volume remains unaffected by changes in temperature and pressure. The computed outcomes from the LAD method align with those derived from nuclear magnetic resonance (NMR), adsorption phase volume (APV), and molecular simulation methods, affirming the accuracy and applicability of the adsorption phase density determined via the LAD method. It is envisaged that these research findings will enhance the precise determination of adsorption phase density and assist in discerning the occurrence state of deep coalbed methane and, potentially, carbon dioxide sequestration.

Research and Application of Coal Seam Permeability Improvement Technology by Sectional Directional Hydraulic Fracturing

To address the challenging issue of gas control in the working faces of the Hegang mining area, based on segmented directional hydraulic fracturing technology, ABAQUS simulation software was employed to simulate and analyze the fracturing process of coal-rock masses under the action of segmented hydraulic fracturing. The study focused on the engineering application research within the mining roadway of the 23# coal seam in the Junde Coal Mine, China. The results indicate that the numerical simulation analysis reveals elliptical patterns in the stress, strain, and fracture width variation of the coal-rock masses influenced by the fracturing action. The width of the fractures exhibits a periodic variation pattern, initially increasing and then slightly decreasing with the injection of water pressure. Additionally, each successive variation shows a decreasing magnitude. After applying segmented hydraulic fracturing technology, the average gas extraction concentration increased by a maximum of 1.73 times, the average mixed flow rate increased by a maximum of 2.16 times, and the average gas extraction pure quantity increased by a maximum of 3.10 times. Segmented hydraulic fracturing can effectively improve gas extraction efficiency, reduce coal seam gas content, and have a depressurizing effect on coal-rock layers. The research findings provide new means for safe and efficient coal mining, particularly in enhancing gas extraction efficiency, alleviating strata pressure, and preventing gas disasters.

Gas desorption law of coal particles and calculation method of gas loss during fixed‐point closed sampling

AbstractWith the application of new technologies for coal mine gas control, it has been increasingly urgent to apply the fixed‐point closed sampling (FPCS) technology for accurate measurement of coal seam gas content. In this study, gas desorption during FPCS was analyzed. In addition, gas desorption experiments and COMSOL simulations were conducted on coal particles. Furthermore, the gas desorption law during FPCS was compared with that under atmospheric pressure. The results show that Sun's formula can effectively characterize the gas desorption law during FPCS, and the i value remains unchanged when the gas desorption curve is fitted with Sun's formula. On this basis, a specific method for calculating gas loss during FPCS by using Sun's formula was proposed. The research findings are expected to provide a theoretical basis for accurate measurement of coal seam gas content by means of FPCS.

Research on Hydraulic Fracturing Pressure Relief and Improvement Permeability Technology of the Soft Coal Seam Roof.

Aiming at the characteristics of low permeability and large gas content of deep soft coal seam, hydraulic fracturing pressure relief and improvement permeability technology of the roof are proposed. FLAC3D was used to invert the roof hydraulic fracturing of the soft coal seams. On this basis, the dynamic evolution characteristics of permeability before and after fracturing were given by the COMSOL multiphysics software. Finally, roof hydraulic fracturing technology was applied on the site. The results show that after the hydraulic fracture of the roof, the peak stress on both sides of the roadway is reduced by 1.7 MPa, the peak stress concentration in front of the roadway is reduced by 2.2 MPa, the stress concentration range is reduced, and the stress is effectively transferred to the deep part of the roadway. After fracturing, the permeability of the stress concentration area increased by 2.18 times, the permeability of the original rock stress area increased by 1.84 times, and the gas fluidity improved. After roof hydraulic fracturing, the occurrence of a coal cannon decreases from 2 to 4 times per 1 m driving to 0 to 1 times, and the phenomenon of a coal cannon at the working face decreases significantly. The concentration of the return air flow is reduced from 0.5-0.9% to 0.2-0.4%. The results of this study have a guiding role in taking the corresponding measures for gas disaster prevention and control.

Influence of geological factors on gas content of the deep coal seam in the northern DJ block, Southeast Ordos Basin, China

Influence of geological factors on gas content of the deep coal seam in the northern DJ block, Southeast Ordos Basin, China

Influence of geological factors on gas content of the deep coal seam in the northern DJ block, Southeast Ordos Basin, China

Influence of geological factors on gas content of the deep coal seam in the northern DJ block, Southeast Ordos Basin, China

Experience of coalbed methane extraction in the Karaganda coal basin

This article discusses the issues of ensuring the safe conduct of mining operations in coal mines. Ensuring the safety of coal industry workers is an urgent problem today. The gas content of the layers increases with the depth of their occurrence and is a deterrent factor in the extraction of minerals. Sudden methane emissions can provoke a large number of human casualties, financial losses, and other consequences. In recent years alone, such accidents have claimed more than 157 human lives in the mines of the Karaganda coal basin. However, by solving this important problem, you can get associated gas. It is not easy to reduce the gas content using existing degassing technologies. The formations have almost zero gas permeability and low gas output at the current depths of their development. That is why it is necessary to have an impact on the coal seam as early as possible in order to ensure the release of methane. This process will make it possible to obtain associated gas, which can be used for the needs of industry or the national economy. As a result, reducing the gas content of coal seams will reduce the risks of mining operations and increase labor safety.

Analysis of Coalbed Methane Production Characteristics and Influencing Factors of No. 15 Coal Seam in the Shouyang Block

Based on the basic geological data and production data of coalbed methane wells in the Shouyang Block, the characteristics and influencing factors of coalbed methane well production were analyzed, and the primary controlling factors were identified by the grey correlation method. The results show that the average daily gas production of the coalbed methane wells in the study area for the single mining of No. 15 coal ranges from 0 to 604.34 m3/d, with an average of 116.82 m3/d. The overall average gas production is relatively low, with only 7 of the 42 wells having an average gas production greater than 200 m3/d. Gas production tends to increase as the gas content increases. There is a significant positive correlation between gas saturation and average gas production. Burial depth and coal seam thickness also show a positive correlation with average gas production. On the other hand, there is a negative exponential relationship between average gas production and critical desorption pressure. Permeability, as determined by well tests in the area, exhibits a negative correlation with the gas production of coalbed methane wells. The correlation between gas production and the mean three-dimensional stress is weak. As the fractal dimension D value of fractures increases, gas production decreases. A smaller difference in horizontal principal stress is more favorable for the formation of network fractures, facilitating reservoir fracturing and resulting in better reconstructive properties. Moreover, an increase in the sand–mud ratio leads to a decrease in average gas production. The correlation between fault fractal dimension and average gas production is weak. The grey correlation method was employed to determine the controlling factors of coalbed methane production in the study area, ranked from strong to weak, as follows: coal thickness > fracture fractal dimension D value > gas saturation > coal seam gas content > horizontal stress difference coefficient > permeability > critical desorption pressure > mean value of three-dimensional principal stress > coal seam burial depth > sand–mud ratio > fault fractal dimension.

The geological factors affecting gas content and permeability of coal seam and reservoir characteristics in Wenjiaba block, Guizhou province

The gas content and permeability of coal reservoirs are the main factors affecting the productivity of coalbed methane. To explore the law of gas content and permeability of coal reservoirs in the Zhijin area of Guizhou, taking No.16, No.27 and No.30 coal seams in Wenjiaba mining area of Guizhou as the engineering background, based on the relevant data of coalbed methane exploration in Wenjiaba block, the geological structure, coal seam thickness, coal quality characteristics,coal seam gas content and permeability of the area were studied utilizing geological exploration, analysis of coal components and methane adsorption test. The results show that the average thickness of coal seams in this area is between 1.32 and 1.85 m; the average buried depth of the coal seam is in the range of 301.3–384.2 m; the gas content of No.16 and No.27 coal seams is higher in the syncline core. The gas content of the No.30 coal seam forms a gas-rich center in the south of the mining area. The buried depth and gas content of coal seams in the study area show a strong positive correlation. Under the same pressure conditions, the adsorption capacity of dry ash-free basis is significantly higher than that of air-dried coal. The permeability decreases exponentially with the horizontal maximum principal stress and the horizontal minimum principal stress. The horizontal maximum primary stress and the flat minimum prominent stress increase with the increase of the buried depth of the coal seam. The permeability and coal seam burial depth decrease exponentially. This work can provide engineering reference and theoretical support for selecting high-yield target areas for CBM enrichment in the block.

Prevention and Control of Coal and Gas Outburst by Directional Hydraulic Fracturing through Seams and Its Application.

The regionalized pressure relief, permeability enhancement, and outburst prevention of "three high and one low" coal seams with high gas, high ground stress, high outburst risk, and low permeability have become important problems to be solved urgently in realizing the sustainable development of coal mines. In this study, a combination of theoretical research, RFPA2D-Flow numerical simulation, and field test was used to study the initiation mechanism and propagation law of directional hydraulic fracturing fractures through the seam. The results show that fracture initiation depends on the axial and radial horizontal stress of the fracture hole, the physical and mechanical properties of coal and rock, and the inside of the weakest layer. Single-hole hydraulic fracturing can achieve a pressure relief radius of 7-8 m, but there is a stress concentration zone outside, which is not conducive to regional pressure relief and permeability enhancement. Directional hydraulic fracturing with multiple holes produces an approximate cylindrical compression and crushing ring and a penetrating fracture surface along the center line of the pressure crack hole and the directional hole, which better eliminates the phenomenon of stress concentration in nondirectional hydraulic fracturing. The technology was applied to the 2238 auxiliary roadway of Chengzhuang Mine of Jinmei Group, and the field implementation results showed that field implementation results showed that directional hydraulic fracturing through the seam reduced the gas content in the coal seam to a great extent, and the coal seam gas content was reduced by about 42.3%, indicating that the technology can effectively reduce the risk of coal and gas outbursts.