Coal Seam Gas Content Research Articles

Prediction of gas emission based on grey-generalized regression neural network

Coal mine gas is one of the main factors endangering mine safety in China, and the amount of gas emission is affected by a variety of related factors, which have the characteristics of non-linearity and uncertainty. In order to predict gas emission more quickly and accurately, a coupling algorithm of grey theory (GM (1,1) and generalized regression neural network (GRNN) is proposed. Thirteen parameters, such as coal seam gas content, depth and GM (1,1) gas emission prediction value, are used as input of the model. The input parameters are normalized and used as training and testing samples of the model. The 10 fold cross validation and minimum root mean square error (RMSE) are used to find the optimal smoothing factor (spread), then a non-linear prediction model of gas emission is established. The gas monitoring data of Qianjiaying Mining Area of Kailuan Mining Group from May 2007 to December 2008 are used in the experiment. The results show that the model has a great improvement in convergence speed and a good accuracy, which can provide theoretical basis for the prevention and control of coal mine gas disasters.

Gas Data Prediction Based on LSTM Neural Network

To improve the prediction accuracy of the coal seam gas content in the unmined areas, based on the analysis and study of the main geological factors affecting coal seam gas content, fuzzy mathematics is used as a means of expressing and processing inaccurate data and fuzzy information and neural network as a way to solve the problem to combine fuzzy mathematics with neural network organically and establish a coal seam gas content prediction model based on LSTM neural network. The results of this study show that the LSTM neural network model can not only solve the problems of difficulty to express fuzzy information quantitatively and determine the learning samples, etc., but also extract the non-linear relationship between the coal seam gas content and its various influencing factors accurately. According to the instance operation verification, the prediction accuracy is improved by 4.84% ∼ 25.79% compared with that of the neural network model. The effect of application to the prediction of coal seam gas content is more ideal. It has a good application prospect and can provide a theoretical basis for implementing scientific mine gas management and preventing various gas accidents.

Study on Geological Structure and Gas Content Occurrence Regularity of Gas Mine

This paper systematically analyzes the distribution characteristics of geological structure of high gas mine, discusses the influence of geological structure on coal seam gas deposit, and obtains the distribution law of gas in the mine. The relationship between the original gas content of coal seam and the factors such as elevation of bottom plate, depth of coal seam and thickness of overlying bedrock is established. Then effectively guide the coal mine gas management, for the mine coal bed gas reserve budget and gas extraction standard effect evaluation provides a reference.

Risk Assessment of Gas Explosion Disaster Based on Random Forest Model

The risk assessment of gas explosion is difficult to determine due to multiple factors. To solve this problem, a random forest model is applied to the risk assessment of gas explosion disasters in coal mines. Based on the disaster system theory, the pregnant environment, disaster factors and disaster-receiving bodies were used as secondary indicators, and the corresponding 24 tertiary indicators were selected as the evaluation indicator system. The example analysis shows that the accuracy rate of gas explosion risk category prediction of the random forest model is very high (up to 100%), and it is highly practical for small sample problems with high data dimensions; Coal seam spontaneous ignition period led to an average reduction of accuracy of 0.2 and caused the Gini index to drop by an average of 1.5. The average accuracy decrease caused by the qualified rate of air volume at the wind-use site and the coal seam gas content is almost 0, and the decrease of the average Gini index is less than 0.15.

Prediction of Residual Gas Content during Coal Roadway Tunneling Based on Drilling Cuttings Indices and BA‐ELM Algorithm

In order to predict the residual gas content in coal seam in front of roadway advancing face accurately and rapidly, an improved prediction method based on both drilling cuttings indices and bat algorithm optimizing extreme learning machine (BA‐ELM) was proposed. The test indices of outburst prevention measures (drilling cuttings indices, residual gas content in coal seam) during roadway advancing in Yuecheng coal mine were first analyzed. Then, the correlation between drilling cuttings indices and residual gas content was established, as well as the neural network prediction model based on BA‐ELM. Finally, the prediction result of the proposed method was compared with that of back‐propagation (BP), support vector machine (SVM), and extreme learning machine (ELM) to verify the accuracy. The results show that the average absolute error, the average absolute percentage error, and the determination coefficient of the proposed prediction method of residual gas content in coal seam are 0.069, 0.012, and 0.981, respectively. This method has higher accuracy than other methods and can effectively reveal the nonlinear relationship between drilling cuttings indices and residual gas content. It has prospective application in the prediction of residual gas content in coal seam.

Analysis of the mechanism of temperature influencing methane adsorption in coal from perspective of adsorbed layer thickness theory

Temperature is an important factor influencing gas content in coal seam. The adsorbed layer thickness in coal has not been quantitatively analyzed under different temperatures. To probe the temperature evolvement and its effect on methane adsorbed layer thickness in coal, the adsorbed layer thickness equation is established based on thermodynamic principles. The adsorbed layer thickness increases with decreasing temperature and increasing equilibrium pressure. The low temperature can promote methane adsorption and increase the number of adsorbed layers. When the pore size is larger than the pore radius at which capillary condensation occurs, the adsorbed layer thickness will decrease as the pore radius increases. This phenomenon shows a negative exponential function. If the pore radius increases to a certain extent, the number of adsorbed layers does not change with the increasing pore radius. The number of adsorbed layers in the micropores and mesopores are greater than that in the macropores. The adsorbed methane quantity can be calculated by the pore size distribution function and adsorbed layer thickness function under different temperatures. The adsorbed layer thickness theory not only reveals the mechanism of temperature influencing methane adsorption in coal but also can be used to predict the adsorption isotherms at different temperatures and pressures if the pore size distribution is known.

Gas comprehensive prevention and control technology and practice in outburst mine

In view of the present situation of gas occurrence in Xiaoxi coal industry, combined with the problems of high gas pressure, high content and complex geological structure in the gas control, the comprehensive gas prevention and control technology to meet the mining connection is proposed.It mainly includes the pre drainage measures of underground kilometer drill hole, through layer drilling and bedding drilling, comprehensive gas prevention technology of surface well pre drainage of coal seam gas and underground cross layer drilling area outburst prevention. The practice shows that after the implementation of comprehensive gas control measures, the residual gas content and gas pressure of coal seam are greatly reduced, and the gas control effect is remarkable. Through the comprehensive gas control technology of outburst mine, the gas control level of Xiaoxi coal industry has been significantly improved, and the number of times of gas overrun has decreased year by year.

Technical Parameters of Hydraulic Punching in a Typical Coal Seam and an Investigation of Outburst Prevention Effect: A Case Study in the Machi Mine, China

The Dengfeng coalfield belongs to the typical “three soft” coal seam and has a high gas content ranging from 10 to 13 m3/t, and the coal seam gas content reaches a maximum 13.69 m3/t. Because of its coal seam occurrence, no protective layer can be mined. The conventional regional pre-pumping measures have several problems. For example, the construction of a pre-pumping borehole is difficult, and it easily causes a coal and gas outburst. The low permeability and rheological characteristics of the coal seam lead to the collapse of the borehole and seriously affects the drainage effect. The influence radius of the drainage borehole is small, which results in a larger quantity of new drilling boreholes and significantly increases the operational cost. Compared to the conventional regional pre-pumping measures, floor roadway hydraulic flushing rapid outburst technology can effectively overcomes these issues. Hydraulic flushing uses water to flush the borehole, and the newly formed fractures and the release of free gas greatly reduce the elastic potential and gas expansion energy of coal and rock, which thus significantly improve the permeability of the coal and improve the coal seam degasification efficiency for outburst risk control. In this paper, a hydraulic punching method is utilized for coal seam stimulation in the Machi mine. Reasonable technical parameters of hydraulic punching were obtained: the water pressure of punching and breaking coal is 8–15 MPa, and the equivalent diameter of the hydraulic punching nozzle should be < 7.47 mm. After the implementation of the hydraulic punching measures, the gas extraction capacity of the coal around the borehole is greatly improved. For 90 days gas extraction after stimulation, the gas content of the 11,061 lane decreased from 8.42–12.12 m3/t to 3.09–5.75 m3/t, relieving pressure and increasing permeability of “three soft” coal and simultaneously eliminating the outburst danger of the coal seam.

Numerical assessment of the critical factors in determining coal seam permeability based on the field data

Accurate acquisition of the coal seam permeability is of great significance to gas drainage. Field measurements are more reliable to determine the coal permeability than laboratory. The Radial Flow Permeability (RFP) measurement is the most used field measuring method to measure the coal seam permeability in Chinese coal mines. The theoretical basis of the RFP method is the single-porosity medium flow theory and the gas content in coal seams is described by a parabolic equation. However, coal is a typical dual-porosity medium. The simplifications may lead to nonnegligible influence on the accuracy of the RFP method, which are not well documented in the literature. In this paper, three different mathematical models of gas flow in coal seams are established. The field gas flow data was matched by these three models to prove the reliability of these models. Then the influences of single-porosity simplification and the parabolic gas content simplification on the accuracy of the RFP method were investigated by comparing the differences of gas flow rates and gas pressures. Results show that there are apparent deviations of gas flow rate and gas pressure between these three models. The precision of the RFP method rapidly reduces with the increase of cleat spacing, which is induced by the single-porosity simplification; the precision decreases with the increase of Langmuir volume, first increases and then declines with the increase of Langmuir pressure, which are led by the gas content simplification. Moreover, because of the imperfections of the numerical calculus in the derivation of the RFP method, the calculated value is always smaller than the true value of coal seam permeability.

The influence of temperature on methane adsorption in coal: A review and statistical analysis

The capacity of coal to adsorb methane is greatly affected by temperature and, in recent years, temperature-dependent adsorption has been studied by many researchers. Even so, comprehensive conclusions have not been reached and conflicting experimental results are common. This paper reviews the current state of research regarding the temperature-dependent adsorption of methane in coal and catalogs the conclusions from experiments conducted on that subject by 28 researchers, as published between 1995 and 2017. Probability theory and statistics are used to show that the conclusion generally accepted by most researchers is that the amount of methane adsorbed by coal decreases with increasing temperature. It is highly likely that the Langmuir volume decreases as the temperature rises, and it is also probable that the Langmuir pressure increases at higher temperatures. Equations are presented that express the relationships between methane adsorption, Langmuir volume, Langmuir pressure, and temperature. Future research should be directed toward determining the relationship between Langmuir pressure and temperature. The results of the study presented herein provide a theoretical basis for predicting the gas content in coal seams and improving the efficiency of coalbed methane development.

CBM geological characteristics and exploration potential in the Sunan Syncline block, southern north China basin

The Permian coal-bearing strata in the Sunan Syncline block contains abundant coalbed methane (CBM) resources. However, systematic studies of CBM geological characteristics in the block are still lacking which severely hinders the CBM development. This paper presents a synthetic study of the CBM geological characteristics in the block from the aspects of gas accumulation conditions and geological controls. Results show that the coal seams are dominated by medium-to high-volatile bituminous coals with the coal structure of normal and cataclastic, possessing relatively high fracability and permeability. The total thickness and gas content of the main coal seams are 9–12 m and 2–21 m3/t, respectively. The CBM in the shallow and deep parts of the block shows the feature of secondary bacterial gas and thermogenic gas, respectively. The roof lithologies of the coal seams and the structure types in the block provide good gas sealing conditions for CBM. In addition, the groundwater migration from the flanks to the axial region of the Sunan Syncline leads to relatively high gas content in the deep part of the block. Based on the CBM geological characteristics, the CBM exploration potential in the block was evaluated, and 2 zones were selected as favorable targets for CBM exploration.

Determination of Gas Content in Low Permeability and High Gas Coal Seam

The determination of coal seam gas content is of great significance to the study of coal seam gas occurrence law and gas prevention technology. There are direct and indirect methods for the determination of gas content in coal seam. Both direct and indirect methods have their advantages and disadvantages, but the results of direct measurement have more disadvantage than indirect measurement. In this paper, the gas content in No. 1 coal seam of Weijiadi Coal Mine is determined by indirect measurement method. The gas content in No. 1 coal seam is calculated to be 8.1m3/t, which is important for gas geological division and precise gas extraction.

Gas content prediction and gas cascade control based on gas geological unit

The division of gas geological units in coal mine is the basis of studying the occurrence law of gas geology in coal mine field, which is of great significance to the prediction of regional gas content and gas emission. Taking Weijiadi coalfield in Jingyuan mining area of Gansu Province as an object, this paper divides the coalfield into gas geological units, according to the gas content of coal seams in different regions, targeted gas extraction measures are implemented, gas cascade control is implemented, regional gas abnormal emission is strictly prevented, and mine safety production is ensured.

Framework for innovative determination of natural gas content in coal seams

The article discusses the development framework of the method and device for high-accuracy measurement of coal seam gas content. It is proposed to design a device ensuring full measurement of gas content of coal core from the moment of coring (drilling at a distance of 4 – 6 m from coal boundary in the gateway face) to sealing of a core in the thermobaric flask (chips reception container). The results obtained using thermobaric flasks are essential. For another thing, the authors consider the requirements imposed on a portable flow rate meter and on the device for gas measurement and recording during drilling in coal seam. The anticipated difficulties in determination of volume of gas release from borehole walls in the total volume of gas measured during drilling are described. Alongside with the production benefits, the device being developed will provide determination of up to 20 gas-kinetic and gas-dynamic characteristics of coal, which can offer new knowledge on the nature of coal-and-methane substance.

Evaluation of safe (by gas criterion) process parameters for longwalls and gateways based on operational gas content measurement in coal seams

The article describes the effect exerted by variability of gas content of coal seam on its mining process parameters: geometry of longwalls, directions and velocities of face advance in longwalls and gateways, as well as overmining and (or) undermining of close-spaced seams. The results are applicable in efficient mine layout and safe mining design.

Effect and mechanism of geological structures on coal seam gas occurrence in Changping minefield

AbstractThe main factor affecting the gas content in a coal seam is the geological structure, and different types of geological structure have different effects on the gas content in a coal seam. To explore the main controlling factors of gas content in coal seam No. 3 in the Changping minefield, and the effect of different geological structures on gas control in a coal seam, this study analyzes the types and quantities of geological structures in the Changping minefield. Further, geological boreholes are used to sample and analyze coal seams near different geological structures and at different burial depths. The results show that the main controlling factor of gas content in a coal seam is the burial depth of the coal seam, and the gas content tends to increase with the increasing depth. A geological structure has an effect on the occurrence of coal seam gas in a local area, and the gas content in the coal seam near a fault is 1.6 times that in the normal areas at the same depth. The gas content in the upper wall of a normal fault is 21.6% higher than that in the lower wall. The syncline and anticline axes are prone to form gas accumulation areas, where the gas content is 30%‐60% higher than the normal level. Gas accumulation is prone to occur around a collapse column, and the gas content there is 2.47 times higher than that in a normal area at the same burial depth. Combining the formation mechanism and structural characteristics of different geological structures, this study analyzes the effect of geological structures on coal seam gas quantitatively and provides a theoretical basis for the prevention and control of gas disasters in the Changping minefield.

Numerical simulation of boreholes for gas extraction and effective range of gas extraction in soft coal seams

AbstractGas disasters are a major factor influencing safe production in mines: Gas extraction can reduce the gas content in coal seams, providing a guarantee of safer production. The parameters for gas extraction are the primary factors influencing the effectiveness thereof. Aiming at the creep properties of soft coal, a fluid‐solid coupling mathematical model considering creep properties of coal was established based on dynamic evolution equation for permeability considering the effects of matrix shrinkage and effective stress. Additionally, by utilizing COMSOL Multiphysics software, the gas extractions from a single borehole and multiple boreholes were calculated. Moreover, the parameters for gas extraction were optimized and applied and tested in field conditions. The result showed the reduction in gas pressure around the boreholes was larger than that from a single borehole when conducting gas extraction from multiple boreholes. The borehole spacing when extracting gas in coal seams by drilling multiple boreholes should be more than twice that of the effective drainage radius. The optimal borehole spacing ranged from 3.2 to 4.2 m for gas extraction lasting 180 d. Numerical simulation was carried out to ascertain the distribution of stress on coal around a roadway. The result revealed that the damage radius of the roadway was 11.8 m, and a reasonable hole‐sealing depth was 12 m. On condition that the borehole spacing during gas extraction from multiple boreholes was 4 m, the reasonable pre‐extraction time was 180 days taking the gas pressure being reduced to &lt;0.74 MPa as a critical point. Furthermore, the gas content, the amount of extracted gas, etc, in a working face after the parameters for gas extraction were optimized were measured. The result suggested that the effect of gas extraction after optimizing parameters conformed to industry standards.

ОЦЕНКА ГАЗОНОСНОСТИ ПЛАСТА К10 В ПРЕДЕЛАХ ШЕРУБАЙНУРИНСКОГО УЧАСТКА КАРАГАНДИНСКОГО УГОЛЬНОГО БАССЕЙНА

Цель: исследование газоносности угольного пласта К10 для оценки ресурсов метана и возможности его добычи на Шерубайнуринском участке Карагандинского угольного бассейна. Методика. Для определения величины природной газоносности угольного пласта К10 Карагандинского угольного бассейна были использованы три методики, основанные на расчетных и фактических данных по газовыделению из пласта при его разработке: 1) расчет газоносности по коэффициентам Лэнгмюра; 2) отбор и обработка проб угля по способу фирмы DMT GmbH &amp; Co. KG; 3) измерение фактического газовыделения. Далее проводилось уточнение указанной величины на основе сравнения результатов, полученных различными способами. Исследования проводились на поле шахты «Абайская» АО «АрселорМиттал Темиртау» при отработке пласта К10. Результаты. Газоносность пласта К10 в пределах Шерубайнуринского участка оценивается в среднем в 17,5 м3/т. Однако способ определения природной газоносности пластов по количеству выделившегося метана дает весьма усредненную величину. Проведенные исследования показали, что результаты определений природной газоносности угольных пластов, выполненных по способу фирмы DMT Gmb&amp;Co, имеют хорошую сходимость с расчётной величиной. Газоносность угольных пластов Шерубайнуринского участка нарастает с глубиной по зависимости, описываемой уравнением регрессии, в общем случае, имеющем вид уравнения Ленгмюра. Результаты исследований показывают, что в практически нетронутом массиве на расстоянии 38…42 м от стенки выработки газоносность постоянна. Научная новизна. Выполнены комплексные исследования газоносности угольного пласта и характера влияния разгрузки на ее величину в Карагандинскомбассейне. Практическая значимость. Сопутствующий добыче угля газ метан при разработке шахт используется для выработки электроэнергии и обеспечения потребностей самой шахты. В будущем на территории Казахстана утилизация угольного метана позволит экономить природный газ и сокращать выбросы парниковых газов. Это перспективный энергетический рынок. Газопроницаемость и метаноносность угольных пластов – это главные критерии оценки метаноугольных площадей при их подготовке к освоению. Исследования газоносности угольных пластов позволят правильно оценивать ресурсы метана и возможности его добычи на Шурубайнуринском участке Карагандинского угольного бассейна

Application of structural equation modeling to evaluate coal and gas outbursts

Coal mines have sudden, usually unexpected expulsions of gas in conjunction with coal into the mine workings. The gas is mainly consisted of methane making this so-called coal and gas outburst a major hazard affecting the safety and productivity of an underground coal mine. Several parameters affect this outburst hazard. In this study, a statistical method namely structural equation modeling (SEM) was applied to identify the relationships between the parameters affecting the coal and gas outbursts for an underground coal mine in Turkey and to analyze multiple interactions between them. The model includes main factors (mining depth, coal seam gas content and moisture content) and contributor factors (seam thickness, seam inclination and distance from fault). The results indicate that mining depth is the most efficient factor in main factors and distance from fault is the most significant contributor to outburst.

A new pattern of underground space‐time tridimensional gas drainage: A case study in Yuwu coal mine, China

AbstractWith the increase of mining depth, the high gassy coal mine confronts with a variety of gas problems, such as gas concentration exceeding the limit in the working face, gas outburst and gas explosion. According to the situation of gas drainage in Qinshui Basin (South of Shanxi Province, China) and enlightened by horizontal directional drillings (HDD) and multi‐branched horizontal wells, a new gas drainage pattern that inverted π‐shape km borehole layout was proposed. Verified in Yuwu Coal Mine, the gas drainage data were standardized via the unified theory of standardization. It could dropped the coal seam gas content to 7.71 m3/t, and increased the gas drainage rate to 34.2%, which conformed to the Chinese regulation (&lt;8 m3/t, &gt;30%, respectively). This pattern has a significant effect on coal mines with a single seam, where protective seam mining technology was unsuitable to prevent gas outburst and gas explosion.