Thin Coal Seams Research Articles

The Study of Water Content on the Coal Loading Performance of Thin Coal Seam Shearer Drum by Discrete Element Method (DEM)

ABSTRACTAs the main component of thin coal seam shearers, the drum bears the functions of loading and cutting, and its performance has become an important factor restricting mining efficiency and production safety. In response to the problem of low efficiency in installing thin coal seam shearers, this paper uses the Discrete Element Method (DEM) to study the effects of loading methods, helical angle of drum, drum rotation speed, and particle water content on coal loading rate. Research has found that the coal loading performance of the ejection loading method is much higher than that of the pushing loading method. As the helical angle increases, the average loading rate increases. As the rotation speed increases, the loading rate of wet coal particles gradually decreases. During production and thin coal seam mining, special attentions should be paid to the control of helical angle of drum and drum rotation speed. This study has guiding importance for improving the efficiency of thin coal seam mining.

Study on the “Two-Zone” Heights in Lower Slice Mining Under Thick Alluvium and Thin Bedrock

The extraction of thin bedrock coal seams with thick alluvium poses a challenging issue in the realm of coal safety production in China. Especially for mining under aquifers, knowing the development height of water-conducting fracture zones above the goaf is crucial for coal mine safety and production. Taking the 11092 working face of lower slice mining in Zhaogu No. 1 Mine as an example, the failure transfer process of the overlying strata is analyzed first. On this basis, the development height of the water-conducting fracture zone is predicted using empirical formulas and the BP neural network. According to the empirical formula, the height of the roof caving zone ranges from 6.93 m to 27.72 m, while the height of the water-conducting fracture zone ranges from 22.17 m to 71.73 m. The BP neural network predicts that the development height of the water-conducting fracture zone in the working face after mining is 56.83 m. CDEM numerical simulation is employed to analyze the development height of two zones of overburden rock. The findings indicate that with a mining height of 2.5 m and a cumulative mining height of 6 m, the maximum caving ratio is 2.61. It is observed that for a cumulative mining thickness of less than 6 m, a bedrock thickness of not less than 30 m, and a clay layer thickness exceeding 5 m, the clay layer effectively obstructs the upward development of the water-conducting fracture zone. Finally, the prediction results of the development height of the two zones of overlying strata in the working face are verified by using the height observation method on the underground water-conducting fracture zone and the borehole peeping method. In conclusion, the height of the overlying strata after mining the lower slice working face in the first panel of the east can be used as a basis for determining the thickness of coal (rock) pillars for waterproofing and sand control safety during the mining of lower slice working faces in mines.

Multi-scale reservoir response characteristics of coalbed methane development through stress relief via horizontal well cavity completion in tectonically deformed coals

China’s coalbed methane (CBM) resources hold significant potential. However, the widespread presence of soft and low-permeability tectonically deformed coal (TDC) presents a challenge to the efficient development of CBM. The development of CBM through stress relief via horizontal well cavity completion (HWCC) offers a promising innovative solution to this problem. To elucidate the multi-scale reservoir response characteristics of CBM development through stress relief via HWCC in TDCs, this article comprehensively employs particle discrete element and finite element numerical simulation methods, and carries out the numerical simulation studies of cyclic seepage at the specimen scale, HWCC at the coal seam scale, and CBM development at the coal seam group scale. The main findings are summarized as follows. Unlike the stress-compression specimens, which exhibited overall failure, the differential distribution of pressure gradients within the specimens during the gas seepage experiments resulted in the development of microcracks concentrated at the bottom of the specimens. With the escalation of coal body structural damage, the permeability stress compression coefficient during the elastic deformation stage shows an increasing trend. Upon entering the plastic deformation stage, the specimen’s permeability shifts from a decreasing to an increasing trend. Increasing the lower limit pressure ratio, upper limit pressure ratio, and cycle rate of gas injection pressure could accelerate the failure efficiency of the specimens. Increasing the lower limit pressure ratio has a more pronounced effect on the TDC specimens, while increasing the upper limit pressure ratio has a more significant impact on the primary undeformed and cataclastic coal specimens. In TDCs, the phenomenon of wellbore collapse and cavity expansion becomes more pronounced. The cavity volume tends to increase with the increase in the initial well diameter, in-situ stress, and alternating bottom-hole pressure differences. The HWCC could enhances reservoir permeability and production in both the cavity completed and adjacent coal seams. For two horizontal wells with cavity completions in the same layer, excessively close well spacing is unfavorable for fostering inter-well interference and reservoir pressure drop. When the HWCC is applied to thin coal seams, the enhancement of permeability and production is limited. Reasonable optimization of drainage rates could effectively mitigate the reservoir permeability velocity-sensitive damage. The research findings extend related theories and provide a robust reference for subsequent practical engineering applications.

Failure characteristics of overlying strata and mechanism of strong ground pressure during the large‐scale and continuous mining of deep multi working faces

AbstractIn this study, a three‐dimensional large‐scale numerical model is established to investigate the failure characteristics of overlying strata and mechanism of strong ground pressure induced by excavation disturbance from multiple working faces. The characteristics of overlying strata fractures, heights of the caving zone and the fracture zone, and evolution of the stress field are systematically analyzed. The numerical simulation results reveal that the height of the caving zone after mining is 8.1 m, and that of the fracture zone is 27.3 m under the conditions of gently inclined thin coal seams. These findings are consistent with the theoretical results. The fracture development process can be divided into three stages: extensive development of new fractures, partial compaction of fractures, and closure of numerous fractures. In the structure of the post‐mining overlying rock, four stress zones are identified as follows: two zones of stress concentration at both ends of the working face, respectively, a zone of relatively high stress at the middle of the working face with low overlying strata, and a zone of stress fully released at the middle of the working face with high overlying strata. Comprehensive analysis of the maximum vertical stress of the cross section and the stress of the working face indicates that the stress increases significantly when mining enters the gob square stage and the roof does not collapse timely.

Research on Hotspots and Evolutionary Trends in Coal Mine Gas Prevention

Mine gas accidents have received widespread attention at home and abroad, because mine gas accidents often cause casualties and property losses once they occur. This study was conducted in order to have a more comprehensive understanding of the research status of and research hotspots in coal mine gas management at home and abroad, and to provide references for relevant researchers’ studies and literature searches. Using the Web of Science (WOS) core database as the data source, this paper analyzed the data from the period of 2000–2023 under the headings of “gas governance”, “Gas Control Technology”, “Pre-mining gas methods in coal mines”, “Methods of Gas Mining in Coal Mines”, “Post-mining gas”, and “Post-mining gas methods in coal mines”. “Methods in Coal Mines”, “Methods of Gas Mining in Coal Mines”, and “Post-mining Gas Methods in Coal Mines” were searched, and the CiteSpace tool was utilized to provide a multi-dimensional visual presentation of the literature, including authors, the number of journals issued, countries of issue, keywords, etc., in order to explore the research hotspots in this field. The analysis results show the following: the development process in the field of gas prevention and control is mainly divided into the three stages of initial exploration, steady development, and explosive surge; China, Australia, and the United States are the top three countries in terms of the number of articles published, and they have a greater influence in the field, but there is a closer connection between the regions in Europe; a certain group size has been formed by the researchers and research institutes in this field, the China University of Mining and Technology is more active in this field, ranking as the first in terms of the number of articles issued, and it has a cooperative relationship with many universities; Kai Wang and Enyuan Wang are the core authors in this field, while C. Ozgen Karacan also has a large body of research in the field, and his research results are widely recognized; the main journals issued in this field are Fuel and Energy Policy, while other journals have been frequently cited, and these journals have an important role in the field. In these journals, “Coal mine methane: A review of capture and utilization practices with benefits to mining safety and to greenhouse gas reduction” is one of the most important articles in the field. Thin coal seams, coal mining workings, and coal and gas protrusion are current research hotspots.

Identification and Application of Wave Field Characteristics of Channel Waves in Extra-Thick Coal Seams

Channel wave seismic activity often occurs with thin and medium-thick coal seams being the main target layer. To address the problem of channel wave applicability detection in extremely thick coal seams, the propagation and identification characteristics of channel waves remain the focus of research. Therefore, this paper takes the in-seam wave exploration of a 27 m extremely thick coal seam as an example and uses the staggered mesh finite difference method to construct a three-dimensional medium model for numerical simulation. An analysis of the physical parameters of coal and rock, along with the dispersion characteristics of channel waves in extra-thick coal seams, is utilized, through the Zoeppritz equation and the total reflection propagation method, to calculate the imaging. We found the following: (1) The dispersion areas and weak dispersion areas along the detection direction are extremely thick coal seams. (2) There are apparent channel waves in extra-thick coal seams, with a waveform similar to body waves; the length of the wave train is shorter than that of the conventional channel wave, and the arrival time can be estimated accurately. The amplitude of the apparent channel wave is affected by the degree of dispersion, with lower attenuation and higher resolution. The characteristic of total reflection in extremely thick coal seams is that the incident angle is equal to the critical angle, and the dispersion characteristics are weak. (3) The channel waves with weak dispersion characteristics in extra-thick coal seams are mainly Love-type waves.

Enhancing Thin Coal Seam Detection in Eastern Indian Coalfields Using ICWT-Decon-Based Seismic Attributes and Acoustic Impedance Inversion

A high-resolution seismic survey (HRSS) is often used in coal exploration to bridge the data gap between two consecutive boreholes and avoid ambiguity in geological interpretation. The application of high-resolution seismic surveys in the Indian context is challenging as the delineation of thin non-coal layers within the coal layer requires a very high seismic data resolution. However, conventional seismic processing techniques fail to resolve thin coal/non-coal layers and faults, which is crucial for the precise estimation of coal resources and mine economics. To address these issues, we applied the inverse continuous wavelet transform deconvolution (ICWT-Decon) technique to post-stack depth-migrated seismic sections. We examined the feasibility of the ICWT-Decon technique in both a synthetic post-stack depth-migrated model and 2D/3D seismic data from the North Karanpura and Talcher Coalfields in Eastern India. The results offered enhanced seismic sections, attributes (similarity and sweetness), and acoustic inversion that aided in the precise positioning of faults and the delineation of a thin non-coal layer of 4.68 m within a 16.7 m coal seam at an approximate depth of 450 m to 550 m. This helped in the refinement of the resource estimation from 74.96 MT before applying ICWT-Decon to 55.92 MT afterward. Overall, the results of the study showed enhancements in the seismic data resolution, the better output of seismic attributes, and acoustic inversion, which could enable more precise lithological and structural interpretation.

Research on the Development Height Prediction Model of Water-Conduction Fracture Zones under Conditions of Extremely Thin Coal Seam Mining

Addressing the difficult problem of predicting the height of water-conducting fracture zones in shallow and thin coal seams, a prediction model of water-conduction fracture zones based on a backpropagation (BP) neural network was developed by integrating theoretical analysis, field measurements, and algorithmic advancements. Firstly, through overburden migration analysis and correlation tests, the height index system of the water-conducting fracture zone was determined. This system includes mining height, buried depth, dip angle, working face width, and overburden rock lithology, with five groups of characteristic parameters. Then, 35 pairs of minefield-measured data were collected to establish the measured height data set of the water-conducting fracture zone. Secondly, a BP neural network prediction model and a traditional support vector regression (SVR) prediction model were constructed based on a Pytorch framework, and the models were trained and tested by selecting data sets. Thirdly, the optimal prediction model was determined by comparing the model with the empirical model and multiple regression model of mining regulations for coal pillar maintenance and pressure in buildings, water bodies, railways, and main shafts. Finally, a typical mine was selected for application to verify the suitability of the optimal model. The results show that: (1) the predicted value of the neural network model is consistent with the change trend of the measured value, which accords with the theoretical law; (2) compared with traditional forecasting methods, the error of the BP neural network prediction model is stable and the prediction effect is the best; (3) dropout can effectively mitigate mitigation training overfitting, achieve regularization, and improve prediction accuracy; (4) the field application further verified that the BP neural network model is the best for predicting the height of water-conducting fracture zones of extremely thin coal seams, and the research results can provide technical guidance for similar fragile coal seams.

Analysing the application of a flexible formwork pre-cast wall driving roadway along goaf in a large mining height face

The technology of building a retaining roadway along goaf or a protecting roadway with a small coal pillar has been developed and applied for many years, and a satisfactory supporting effect has been obtained in medium–thick coal seam and thin coal seam mining. However, the gob-side roadway or small coal pillar mining in a thick coal seam is still subjected to technical problems occasioned by factors such as high roadway, high support pressure beside roadway, and waste of coal resources. To solve these problems, the author proposes an innovative technology of coal-free mining: the technology of driving roadway along goaf with a flexible formwork pre-cast wall. The article utilizes the 3503 and 3505 working faces of Wangzhuang Coal Industry Group as the research background, and comprehensively introduces the principle of the technology and the overburden rock movement law. Through theoretical calculations and numerical simulations, the support resistance and support parameters of flexible formwork pre-cast walls have been determined and successfully performed in industrial practice. The results indicate that the combination of the flexible mould pre-cast wall coal pillar-free mining technology and roof cutting process is more conducive to the maintenance of the roadway in the lower working face, and effectively reduces the stress and deformation of the surrounding rock. The roof and floor of the drivage roadway move, and the deformation of the two sides is small; furthermore, the overall roadway retention effect is satisfactory, which meets the requirements of mining in the lower working face. The coal pillar pertaining to the 20 m section of the 5 m high mining height face was recovered for Wangzhuang Coal Mine, and the recovery rate of the coal resources and the driving speed of the roadway were improved. The proposed method can be popularised and applied in this mine and even in the mining of 15# large-height coal seams in the two cities.

Study on Critical Width of Semi-Coal Rock Roadway of Shallow-Buried Thin Coal Seam Based on Coal Side Self-Stabilization

In the context of a shallow-buried thin coal seam, the surrounding rock deformation in the semi-coal rock roadway is comparatively small, resulting in self-stabilization of the two sides of the roadway without the need for support when the roadway is below a critical width. This study focuses on the transportation roadway of the 2107 working face in the Anzhe Coal Mine, employing a combination of laboratory tests, field tests, theoretical analyses, and numerical simulations. A mechanical model for the layered roof of the semi-coal rock roadway in a shallow-buried thin coal seam is developed, along with a calculation formula for determining the critical width of such roadways. The study also initially examines the correlation between the critical width and factors such as the tensile strength of the roof, the buried depth of the roadway, and the thickness of the immediate roof strata under conditions where the coal sides of the roadway are self-stabilizing. The results showed the following. (1) The calculation formula has good applicability for typical shallow-buried mine roadways in the Niuwu mining area and shallow-buried semi-coal rock roadways with coal thickness below 0.7 m under similar geological conditions. The critical width is related to the tensile strength of the roof, the buried depth of the roadway, and the thickness of the immediate roof strata. The degree of influence is determined by the thickness of the immediate roof strata > the tensile strength of the roof > the buried depth of the roadway. Among these, the tensile strength of the roof, the thickness of the immediate roof strata, and the critical width are basically in a positive exponentially increasing relationship, and the buried depth of the roadway and the critical width are basically in a negative exponentially decreasing relationship. (2) The on-site measurement of the loose circle on both sides of the roadway revealed that the rock mass loose circle had a thickness of 0.2 m, while the coal loose circle had a thickness ranging from 0.6 m to 0.7 m, aligning closely with the results obtained from theoretical calculations. The thickness of the coal loose circle on both sides served as the basis for determining the critical width of the semi-coal rock roadway in the shallow-buried thin coal seam. The calculated critical width of the roadway was 2.9 m, whereas the actual width measured was 2.4 m. Consequently, the two sides of the roadway are deemed capable of self-stabilization in the unsupported state. (3) Following the optimization of the support scheme, engineering analysis indicates that the roof and floor exhibit a maximum convergence of 46.3 mm, while the two sides show a maximum convergence of 18.4 mm. It is observed that the surrounding rock of the roadway satisfies the safety requirements for production. This study can provide theoretical support and a scientific basis for the stability discrimination of two sides and surrounding rock control of semi-coal rock roadways in shallow-buried thin coal seams under similar conditions.

Floor Heave Control in Gob-Side Entry Retaining by Pillarless Coal Mining with Anti-Shear Pile Technology

The severe floor heave in gob-side entry retaining is the major restriction factor of the wide application of pillarless mining thin coal seams. Reinforcement and stress-relief floor heave control methods are the most promising. However, in practice, floor restoration is widely used. Therefore, floor heave control technology in gob-side entry retaining needs to be improved. This study proposes anti-shear pile technology to control floor heave in gob-side entry retaining. The research was mainly carried out by numerical simulation. It was found that the transformation of high vertical stresses in the entry floor underneath the filling wall and coal seam body into horizontal stresses starts the floor heave process. The vertical dilatancy of rocks under the roadway span and their subsequent unloading lead to the delamination of the floor strata and uplift of the entry contour. In this paper, the best pile installation scheme was found. It is a 2pile 5+2 scheme with the installation of two piles, each 2 m long. After that, it was shown that filling piles are more than 3.3 times cheaper than comparable analogs, and pile installation is less labor-intensive. The implementation of the proposed floor heave control method leads to a reduction in heaving by 2.47 times.

Thin seams and small mines are associated with higher exposures to respirable crystalline silica in US underground coal mines

ObjectivesPrevious radiologic and histopathologic studies suggest respirable crystalline silica (RCS) overexposure has been driving the resurgence of pneumoconiosis among contemporary US coal miners, with a higher prevalence of severe disease...

Geological engineering double sweet spot evaluation of thin coal seam reservoirs based on facies control: A case study of tight sandstone gas in the Shenfu block of the Ordos Basin

Abstract The development of thin coal layers within the Shenfu tight sandstone reservoirs significantly impacts the control of hydraulic fractures over the actual sweet spots, leading to considerable inter-well production variability. This paper establishes a connection between individual well sweet spots and block sweet spots through a refined lithofacies model and conducts a comprehensive double sweet spot secondary optimization in conjunction with the characteristics of thin coal layer development. The research findings indicate the following: Class I sweet spots ≥0.46, 0.37≥ Class II sweet spots <0.46, 0.3≥ Class III sweet spots <0.37; fractures will be captured by the coal layer if the thin coal layer is more than 5 m away from the perforation point or if the coal layer thickness exceeds 3 m; the secondary sweet spot optimization can eliminate the influence of thin coal layers and establish a three-dimensional comprehensive double sweet spot model suitable for the study area.

Numerical study on the dynamic pressure control for self-forming roadways using CHRCT in thin coal seams with thick and hard roofs

Close-hole roof-cutting technology (CHRCT, also called “dense drilling”) has been widely applied in coal mines due to its economic and safety benefits. Inappropriate cutting parameters and support schemes can lead to dynamic pressure disturbances in self-forming roadways with thick and hard roofs. Moreover, fully characterizing the procedure and process of self-forming roadways using CHRCT in the field is difficult, resulting in unconvincing results. Therefore, this study aims to fill the gaps in theoretical knowledge and methodology. First, the dynamic pressure characteristics of the self-forming roadway using CHRCT were investigated, and the dynamic pressure types of the roadway were classified. There are three main types: roof cut off along the coal wall side of, severe deformation, and overhanging roof of a roadway after the second working face mining. The effects of different hole parameters (inclination angle, depth and spacing) on the roof cutting to form a roadway were also investigated. The optimal hole inclination, depth and spacing of 15°, 8 m, and 200 mm were determined through a series of experiments. Then, three support schemes embedded in the roadway were compared in terms of stress evolution, bolt and cable axial forces, roof displacement, and structure. Finally, this study proposes a dynamic pressure mitigation strategy through the optimization of parameters for close-hole roof-cutting and support schemes, monitoring and controlling ground pressure in roadways, and taking auxiliary measures for pressure relief. The results show that this strategy can effectively eliminate the dynamic pressure of the roadway and meet the stability requirements of the full mining cycle. This paper presents a methodology for analysing CHRCT via numerical simulation. Moreover, this approach is of great theoretical and practical importance for dynamic pressure control for self-forming roadways using CHRCT in thin coal seams with thick and hard roofs.

Study on Gas Control Technology in Soft and Thin Seam with High Gas Content

The problem of gas control in soft and thin seam with high gas content has been puzzling the safety production of coal mine, and the pre-drainage of borehole gas in this seam is one of the effective measures to solve this problem. According to the occurrence characteristics of soft and thin coal seam with high gas content in a mine in Shanxi, this paper studies the reasonable hole sealing depth and drilling construction technology of this coal seam, and determines that the reasonable hole sealing depth of pre-drainage drilling is 18m, and the optimal drilling construction technology is pneumatic directional drilling, which improves the gas pre-drainage concentration of this coal seam to more than 52%, improves the gas control effect of this coal seam, and provides important reference for gas control of other coal seams with similar occurrence conditions.

Astronomical influence of the development of Paleogene thin coal seam groups in offshore Lacustrine basins: A case study of the Zhu I Depression’s Enping Formation located in the northern South China Sea

Astronomical influence of the development of Paleogene thin coal seam groups in offshore Lacustrine basins: A case study of the Zhu I Depression’s Enping Formation located in the northern South China Sea

Influence of coal cowl parameters on the coal loading process of thin coal seam shearer drum

The low loading rate of the thin coal seam shearer drum is a severe obstacle to the efficient mining of thin seam resources, and the auxiliary drum loading through the cowl is an effective measure to alleviate this situation. However, the working mechanism of the coal cowl still remains unclear. In this paper, with the help of the discrete element method and the modeling experiment method, the effects of coal cowl’s offset distance, tilt angle and wrap angle on the coal loading rate under different loading modes of the drum are investigated; and the significance of various factors and their interactions to the drum coal loading rate is explored by designing response surface experiments. The findings show that a monotonous negative correlation between the offset distance of the coal cowl and the coal loading rate is identified, and that a smaller offset distance can effectively improve the coal loading rate of the drum. The conveying torque is significantly increased, easily inducing the drum choking, coal recycling coal over-crushing. Along with the increasing tilt angle, the rate of ejection loading decreases monotonically, and the rate of pushing loading increases first and then decreases. Coal loading rate is weakly affected by changes in coal cowl’s wrap angle. The results of response surface analysis reveal that the most significant factors affecting the drum’s coal loading rate are tilt angle and offset distance in ejection and pushing loading modes, respectively. The conclusions drawn here offer implications for improving the coal loading performance of the thin coal seam shearer drum, as well as certain guidance on the optimal design of coal cowl parameters.

Roof control mechanism and partition compensation support technology of gob-side entry formed by N00 mining method in thin coal seam

Roof control mechanism and partition compensation support technology of gob-side entry formed by N00 mining method in thin coal seam

Roof movement and instability fracture characteristics in shallow-buried thin coal seam conventional mining faces

The variation in the width of the mining face significantly affects the stability of the face, leading to potential roof fracturing and collapse. Additionally, strong mining pressure can manifest, severely impeding the safe production of coal mines. This study uses the No. 16705 conventional working face of Jinda Coal Mine as its engineering background to investigate the characteristics of roof strata movement and instability under conditions of variable-width mining in shallow-buried thin coal seams. First, the dynamic load of the roof strata is estimated based on the key strata theory. Next, a mechanical model of the immediate roof strata movement in the working face is established based on the theory of elastic thin plates, which has been used to reveal the impact of different dimensions of the overhanging plate structure and residual overhanging structures in the corner on roof movement and its associated fracture mechanics. The findings indicated that the maximum bending deformation, deformation moment, and bending stress all have an exponential function relationship with the roof width. Similarly, these metrics have an exponential function relationship with the overhanging span of the roof. In addition, these parameters all have a linear functional relationship with the size of the residual overhanging structures in the corner. Finally, the effect of roof instability on overlying pressure is analyzed, and both the initial fracture step length and cyclic movement fracture step length of the roof are estimated. These insights offer valuable scientific guidance and a theoretical foundation for analyzing the adaptability of load-bearing pillars pressure in thin coal seam mining faces, bearing significant relevance to safety production.

Research on mine pressure law of isolated working face in close-distance thin coal seam under the influence of remaining coal pillar

Research on mine pressure law of isolated working face in close-distance thin coal seam under the influence of remaining coal pillar