Search Results (1,563)

To address the continuous accumulation of carbon monoxide (CO) in the upper corner of working faces in shallow-buried easily spontaneous combustion coal seams, this study takes the 1113 fully mechanized mining face of Yidong Coal Mine in Shaanxi Province as the engineering background and investigates the CO migration characteristics in the upper corner and catalytic oxidation removal technology. First, a CFD model of gas migration in the goaf was established. The reliability of the model was verified by comparing the simulated oxygen concentration distribution characteristics and the range of the spontaneous combustion “three zones” with field monitoring results. Based on the validated model, the distribution and migration characteristics of CO concentration in the goaf were analyzed, revealing the migration process of CO from the goaf to the return air corner and its accumulation characteristics. Independent field monitoring further confirmed the occurrence of persistent CO accumulation and over-limit concentrations in the upper corner, supporting the engineering significance of the CO migration pathway predicted by the CFD model. To overcome the limitations of traditional prevention measures in removing already-formed CO, catalytic oxidation experiments were conducted to investigate the variation characteristics of gas components during CO oxidation under ambient temperature conditions. The effects of oxygen concentration, CO concentration, and catalyst dosage on CO removal performance were also studied. The results showed that the catalyst could achieve efficient CO oxidation removal and demonstrated high activity for low CO concentrations, with 100 ppm and 200 ppm CO being completely eliminated in laboratory tests. In field applications, the upper corner CO concentration was reduced from 80 to 142 ppm to 0–16 ppm. The research results provide a theoretical basis and technical reference for CO control in the upper corner of shallow-buried easily spontaneous combustion coal seams. Full article

The Karatuzi mining area is a key coal resource base in Southern Xinjiang. This paper focuses on Coal Seams No. 3 and No. 6 of the Yangye Formation. Through coal petrology, coal quality and elemental geochemical analyses, combined with assessments of the coalification environment, coal cleanliness grades and direct liquefaction evaluation systems, this study investigates their coalification environments and potential for clean utilisation. The results indicate that both coal seams consist predominantly of the vitrinite group and are classified as medium-rank coals. The ash content of the raw coal ranged from 21.76% to 27.66%; the sulphur content of Coal Seam No. 3 is lower than that of Coal Seam No. 6, whilst the concentrations of Cl, F and As are generally low to moderate. The coalification period of the Yangye Formation was characterised by a generally humid, water-saturated peat bog environment. The raw coal from both Seam No. 3 and Seam No. 6 was classified as Grade IV unclean coal; following flotation, the ash content decreased to 7.31–7.54%, and the cleanliness grades were upgraded to Grade II and Grade III, respectively. Statistical analysis revealed significant changes in moisture content, ash content, volatile matter, sulphur content, fluorine and arsenic. Following flotation, the raw coal attains the potential for use as Grade II coal for direct liquefaction, providing a basis for the quality enhancement and clean utilisation of coal in the mining area. Full article

Historical underground workings in the Maleia–Livezeni sector of the Petroșani Coal Basin were reconstructed from four archival mining plans and a coordinate-referenced Drawing Exchange Format (DXF) dataset. Twelve extraction-sector polygons, principal galleries, exploitation limits, dated mining stages, and 567 internally checked mining-elevation annotations associated with Coal Seam No. 3 were integrated in a geographic information system (GIS) using the Romanian Stereo 70 coordinate reference system (EPSG:3844). Net elevation differences between 2007 and 2026 at seventeen surface benchmarks were used as response variables. Nearest-feature relationships and mining-exposure indicators for 50, 100, and 150 m neighbourhoods were evaluated using exploratory Spearman rank correlations. Among the originally selected 50, 100, and 150 m neighbourhoods, cumulative gallery length within 50 m showed the strongest planimetric association with |Δ_Z| (ρ = 0.734, p = 0.0008, q = 0.010), while extraction-sector coverage and gallery length remained positively associated at broader scales. R19 showed the greatest immediate extraction-sector exposure, whereas R14, which recorded the largest elevation loss, was characterised by a broader concentration of surrounding workings. R09 recorded the smallest elevation change and was approximately 470 m from the nearest reconstructed extraction sector. Cumulative mining configuration was more informative than nearest-sector distance alone for interpreting spatially variable net surface-elevation change in this legacy mining setting and highlighted the limitations of archival GIS reconstruction. Full article

The unclear coupled temperature–pressure control mechanism of deep coalbed methane (CBM) occurrence and the poorly understood transformation law of adsorbed and free gas during geological history have severely restricted the accurate evaluation of CBM resources in the southern margin of the Junggar Basin. Taking the No. 42 main coal seam in the Fukang mining area as the research object, this study combines isothermal adsorption experiments, thermodynamic analysis, and basin numerical simulation to identify the methane adsorption characteristics of coal and their main controlling factors, establishes a CBM content prediction model coupled with coal maceral composition and temperature–pressure conditions, and reconstructs the complete CBM accumulation evolution process over geological time. Isothermal adsorption experiments were conducted at 30 °C over 0–8 MPa (6 pressure points) for all seven core samples, and variable-temperature adsorption experiments were performed on representative sample No. 42-5 at 30, 50, 70, and 90 °C over 0–22 MPa (10 pressure points per temperature). The results show that the average equilibrium moisture-based Langmuir volume of coal samples in the study area is 22.36 m³/t, and the adsorption capacity is significantly positively correlated with fixed carbon content. Pressure dominates the positive adsorption effect in the low-temperature and low-pressure range, while temperature dominates the negative adsorption effect in the high-temperature and high-pressure range. The total gas content first increases and then decreases with depth, reaching a peak of 12.56 m³/t at 900 m; free gas accounts for a larger proportion than adsorbed gas below 3600 m. The central-southern main area of the study area, with a gas content of 11–13 m³/t, is a favorable exploration target. The accumulation evolution four stages: pure adsorption, free gas occurrence, excessive gas expulsion, and uplift adjustment. The proportion of free gas reached its peak during the maximum burial period in the Late Cretaceous. After the Paleogene uplift, hydrocarbon generation ceased, and the total gas content remained at 13.16 m³/t. The coupled research method of “experimental determination–model prediction–evolution simulation” established in this paper realizes cross-validation of CBM content through multiple methods, and can provide theoretical support for deep low-rank CBM accumulation research and resource evaluation. Full article

The Suzhou mining area contains abundant coalbed methane resources. Analyzing the hydrochemical characteristics of formation and drainage water from coalbed methane wells is of considerable importance for the efficient extraction of coalbed methane. Using hydrochemical test data from formation water, produced water, and the main coal seam of four coalbed methane wells, this study systematically investigated the relationship between hydrogeochemical characteristics and drainage water from coalbed methane wells. The results indicate that the trace elements in the main coal seam were similar to those in the water samples from the coal-bearing Permian sandstone aquifer (CPSA), both of which showed elevated levels of Ba. The water samples from the fourth aquifer of the Cenozoic Era (Q4 aquifer) primarily underwent ion exchange between Na⁺ and K⁺ in the water and Ca²⁺ and Mg²⁺ in the formation minerals. The water samples from coalbed methane wells, CPSA, Carboniferous Taiyuan Formation limestone aquifer (CTFLA), and Ordovician limestone aquifer (OLA) primarily underwent ion exchange between Ca²⁺ and Mg²⁺ in the water and Na⁺ and K⁺ in the formation minerals. Full article

While traditional mine hydrogeology focuses on preventing water inrush to protect underground workings, this study establishes a novel evaluation framework aimed at protecting valuable, high-temperature geothermal water resources during deep coal extraction in coal–water dual-resource mines. We selected seven key indicator factors to quantify the disturbance intensity of mining to the overlying geothermal reservoir aquifer, and applied fuzzy variable set theory to evaluate the disturbance level and delineate disturbance zones to investigate the Tongzhe Coalfield area in the eastern Henan Plain of China. The results show that zones of stronger disturbance associated with the extraction of the main coal seam are concentrated in the northern, northeastern, and southwestern parts of the study area. Area statistics indicate that high disturbance zones account for 5.0% of the study area, relatively high disturbance zones for 30.6%, moderate disturbance zones for 32.6%, relatively low disturbance zones for 22.1%, and low disturbance zones for 9.7%. In total, zones at moderate disturbance or above represent 68.2%, suggesting that appropriate mining methods are required during extraction of the main coal seam to mitigate mining induced disturbance to the roof geothermal aquifer. These results provide a scientific basis for selecting mining practices that protect water resources in coal–water dual-resource mining areas. Full article

Deep coalbed methane (CBM) is an important frontier for expanding unconventional natural gas reserves and production in China. Significant vertical heterogeneity in coal reservoirs is a primary constraint on exploration and development, and the conventional interval subdivision based solely on burial depth is insufficient for refined evaluation of deep coal reservoirs. This study targets the No. 8 coal seam of the Carboniferous Benxi Formation in the northern part of the eastern margin of the Ordos Basin. Based on core and logging data from wells F and S, this study applies the Milankovitch cycle identification method and uses the short-eccentricity cycle (∼109 kyr) as a working timescale for high-resolution isochronous stratigraphic subdivision of coal seams within a single well. Combined with coal petrology and reservoir property analysis and the Analytic Hierarchy Process (AHP), this study characterizes vertical heterogeneity and quantitatively identifies favorable intervals in the coal reservoir. The results indicate that: (1) the No. 8 coal seam in Well F was divided into three sections, and Well S into two sections. These subdivisions provide a high-resolution cyclostratigraphic framework for evaluating vertical reservoir variations within each well, with higher resolution than conventional depth-based segmentation (spectral confidence > 99%, p < 0.01); (2) coal quality, pore structure, and gas potential vary significantly with depth, and these variations represent geological responses to periodic changes in depositional environment and sediment supply during peat accumulation; (3) AHP-based quantitative evaluation identifies the upper section of Well F (score: 0.336) and the lower section of Well S (score: 0.755) as the favorable targets for the two investigated wells, characterized by good coal quality, favorable pore structure, and high gas storage capacity. These findings provide geological support for refined deep coalbed methane exploration and development in the study area, and also offer a new technical approach for high-precision stratigraphic subdivision of coal reservoirs. Full article

Scientific evaluation of open-pit slope stability under the disturbance of underground goaf is critical to the safe production of open-pit coal mines. Taking an open-pit coal mine in Inner Mongolia as the engineering background, this study investigates the influence mechanism of underground goaf on slope stability. With discrete element numerical simulation, the movement law of overlying strata above the goaf is revealed, and the heights of the “three zones” and boundary movement angles are determined. Furthermore, limit-equilibrium theory is adopted to analyze slope stability affected by goafs from three perspectives: goaf span, occurrence position and inter-goaf spacing. The results indicate that under partial extraction conditions, goaf span is positively correlated with the height of the caving zone and negatively correlated with the boundary movement angle. As the goaf width increases, the mining-induced deformation field expands progressively, and a distinct bending-subsidence zone develops in the 50 m wide single-goaf case, resulting in a complete caving–fractured–bending-subsidence zonation. For adjacent goafs, smaller inter-goaf spacing promotes overlap of the mining-induced deformation fields and generally enhances overburden disturbance. As the spacing increases, the interaction between adjacent goafs tends to weaken, although the degree of reduction depends on goaf width and the deformation parameter considered. Therefore, the spacing of approximately 50 m observed in the present simulations is interpreted as a site-specific transition range rather than a universal critical threshold. Two landslide modes are identified in the Baozhixil open-pit mine: circular arc sliding and composite sliding controlled by the weak interlayer of No. 1 coal seam. Slope stability is negatively correlated with goaf span and positively correlated with the horizontal distance between the goaf and the slope face. For the analysis of inter-goaf spacing, slope stability shows a positive correlation with the proportion of non-collapse deformation area within the sliding mass. Full article

Coal rib instability is a critical challenge in steeply inclined, large-mining-height longwall faces containing coal seam partings. Taking the No. 4103 working face of Changcheng No. 1 Coal Mine as an engineering case, this study integrates theoretical analysis, numerical simulation, and field verification to investigate the underlying failure mechanisms. A segmented shear–slip mechanical model is developed using limit-equilibrium analysis to derive the stability margin, through which the coupled effects of seam dip, mining height, and parting properties on rib stability are quantified. Three-dimensional distinct-element simulations further reveal that rib deformation follows a consistent spatial pattern—middle section > upper section > lower section—and that the position and number of partings modify the load-transfer path and failure-surface continuity. Based on these findings, a coordinated control strategy is implemented, incorporating zoned differential support, dynamic adjustment of mining parameters, and localized reinforcement. Field application substantially reduces the frequency and depth of rib spalling and improves support stability and production continuity. The results provide a practical basis for coal rib control under comparable steeply inclined, large-mining-height conditions. Full article

Methane production from water-bearing coal reservoirs is governed not only by methane adsorption capacity but also by the accessibility of adsorption domains and the efficiency of pore-scale transport during pressure depletion. However, the interfacial mechanism by which coal wettability and water occurrence regulate methane adsorption–desorption reversibility remains insufficiently understood. In this study, three representative Ordos Basin coal samples with different pore structures and surface polarities, denoted as OBC-L, OBC-M, and OBC-H, were investigated to explore the pore-scale mechanisms governing water-mediated methane storage and release rather than to establish basin-wide statistical relationships. A combined experimental workflow involving N₂ adsorption–desorption, FTIR and XPS analyses, contact angle and Zeta potential measurements, low-field NMR, high-pressure methane adsorption–desorption tests, kinetic modeling, hysteresis evaluation, and Pearson correlation analysis was used to clarify the coupling among pore structure, coal–water interfacial properties, water occurrence, methane storage, and methane release. The results show that OBC-H possesses the strongest dry-state methane storage potential, with the BET surface area increasing from 5.82 m²/g for OBC-L to 12.94 m²/g for OBC-H and the fitted Langmuir volume (V_L) reaching 22.3 cm³/g. Nevertheless, OBC-H also shows stronger water affinity, as reflected by an increase in the XPS-derived O/C atomic ratio from 0.118 to 0.186, a decrease in contact angle from 82.6° to 51.8°, and an increase in bound water fraction from 46.3% to 69.4%. With the transition from dry to saturated conditions, the fitted V_L of OBC-H decreases from 22.3 to 15.2 cm³/g, while the Langmuir pressure (P_L) increases from 1.38 to 3.00 MPa, indicating a simultaneous reduction in the model-estimated maximum methane adsorption capacity and apparent methane affinity. More importantly, the desorption results demonstrate that high adsorption capacity does not necessarily correspond to high methane deliverability. For OBC-H, the final desorption efficiency decreases from 79.6% to 54.2%, the effective diffusion coefficient decreases from 2.74 × 10⁻¹¹ to 0.86 × 10⁻¹¹ m²/s, and the hysteresis index increases from 12.8% to 36.4% under saturated water conditions. Correlation analysis further confirms that bound water fraction is positively associated with adsorption–desorption hysteresis but negatively associated with desorption efficiency, desorption rate constant, and effective diffusion coefficient. These findings are consistent with two distinct water-mediated constraints: adsorbed/bound interfacial water contributes to surface-site shielding, whereas capillary and saturated water occupation contributes to pore-throat transport restriction; together, these effects reduce methane release efficiency and enhancing desorption irreversibility. This study provides an interfacial interpretation of methane deliverability based on representative water-bearing coal samples and offers a mechanistic basis for understanding wettability- and water-retention-related transport constraints; broader applicability across the Ordos Basin requires validation using a larger number of samples from different coal seams and reservoir settings. Full article

Mining-induced subsidence remains a critical concern for mine safety, issues related to surface and underground infrastructure, mine planning and environmental risk. This paper presents a focused critical review that is specifically devoted to mining-induced subsidence prediction using 3D numerical modeling techniques, with its advancements, applications, challenges, and opportunities. It first traces the evolution from empirical, graphical, and influence function approaches to analytical approaches, which include numerical methods and probabilistic methods, and then to statistical and deep-learning-based models for subsidence predictions, highlighting their capabilities and limitations in complex geological conditions. These methods are included to establish the historical and comparative context, while the central focus of the review remains the development, application, calibration, validation, limitations and future use of 3D numerical modeling for mining-induced subsidence prediction. The review then concentrates on 3D numerical frameworks, including continuum (FDM, FEM, and BEM), discontinuum (DEM and DFN-based) and hybrid methods (FEM–DEM/BEM–FEM), covering their historical development, application in coal and metal mines, and strengths for simulating caving, time-dependent behavior and multi-seam conditions. Particular attention is given to geotechnical inputs (in situ tests, inverse analysis, and rock-mass classification); constitutive modeling, including creep and damage; and data assimilation, calibration and validation, using InSAR/MTInSAR, GNSS, and levelling data. The review synthesizes key challenges like geological heterogeneity, uncertainty regarding rock-mass parameters and discontinuities, scale effects, computational demands and human/operational factors and outlines opportunities where 3D numerical models, coupled with probabilistic tools and machine learning techniques which can enhance hazard prediction, infrastructure and water-management planning, regulatory compliance, and community land-use decisions, can be deployed. Overall, the paper concludes that InSAR-calibrated 3D numerical modeling, embedded in transparent calibration/validation workflows, currently provides the most robust foundation for safer and more sustainable mining operations. Full article

To reveal the evolution of overburden movement, slope deformation, and fracture damage during highwall mining, a physical similarity model was established based on the geological conditions of the Heishan Open-Pit Mine, Xinjiang. The excavation extended through the model thickness and was idealized as a continuous slot. Different chamber heights were considered to simulate the extraction of Coal Seam 13-2 and the subsequent mining of the overlying Coal Seam 9. Overburden and slope displacements, fracture-area ratio, and fractal dimension were analyzed using the MatchID-2D digital image correlation method, displacement monitoring, and fracture image processing. The results show that deformation initially concentrates in the chamber roof and lower overburden and subsequently propagates toward the slope toe and surface, exhibiting distinct stage-dependent and spatially differentiated characteristics. As the chamber height increases, overburden subsidence, slope-toe displacement, fracture-area ratio, and fractal dimension all increase. During the extraction of Coal Seam 9, displacement continues to accumulate within the previously formed deformation zones, accompanied by further propagation and coalescence of existing fractures. The results characterize progressive local damage and spatially coordinated deformation within the model. These findings improve understanding of overburden-slope deformation and fracture evolution under the investigated conditions. Full article

The coal–roof/floor combination system is a special geological structure consisting of both coal and roof/floor materials, which often leads to the occurrence of impact failure. The instability and failure of the coal seam are not caused by a single disturbance, but often occur under repeated loading and unloading processes under the action of mining stress. Thus, research on the impact failure, especially the energy evaluation of coal–rock combination materials under cyclic loading and unloading, is of great significance for understanding the rock burst mechanisms of deep coal mines. This paper focuses on the combination material formed by coal seam and roof and floor rock. Taking the #9 coal seam and roof and floor sandstone from the Zhangshuanglou Coal Mine as the test subjects, conventional triaxial compression and cyclic loading and unloading tests were conducted on sandstone, coal, and coal–rock combination material, respectively. Based on the strain energy evolution characteristics, the failure behavior of the coal–rock combination materials throughout the entire process of energy accumulation, dissipation, and release during cyclic loading and unloading are discussed. The research finds that the macroscopic failure behavior of the tested coal–rock combination specimens is dominated by the weaker coal component, and there are marked differences between the tested sandstone and coal components in their respective energy storage capacities, release characteristics, and dissipation behavior. On the basis of these measured differences and of CT-confirmed failure localization within the coal layer, it is inferred—as a mechanistic working hypothesis rather than a directly demonstrated result—that the main driving energy for the impact failure of the coal component may originate from the elastic strain energy stored in the roof/floor sandstone components, released preferentially toward the coal through their interfaces. For mining and excavation at high-in-situ-stress mining areas, the essence of the impact failure of surrounding rock is the non-coordination of energy storage and release between the roof and floor rock materials and the coal seam. The key to preventing impact failure is to eliminate the differences in energy storage and release between different rock materials in the coal seam. Full article

A multifunctional self-aggregation modified quartz sand support agent (MRQS) was prepared by a simple dry coating method for coal seam gas fracturing channels. The organic coating is composed of KH550, OTMS, H-PDMS and microcrystalline wax, which transforms the surface of the raw sand from super hydrophilic to hydrophobic (contact angle is 91.8°), thus providing a driving force for the spontaneous aggregation of particles in aqueous fluids. MRQS shows excellent anti-reflow stability, which does not dissipate after ultrasonic oscillation for more than 10 min, while raw sand can only withstand 3 min. Atomic force microscopy (AFM) analysis shows that the interface adhesion of MRQS under low load is tripled (106.7 nN vs. 32.0 nN), which explains its stronger aggregation intensity. In the temporary sealing test, MRQS forms a stable and low-permeability sealing layer at the narrow crack, raising the sealing pressure to 0.23 MPa, while the original sand cannot achieve effective sealing. The crack diversion ability test shows that MRQS still maintains a diversion capacity of 1.62 μm²·cm under a closed stress of 45 MPa, and the attenuation curve is gentle. Although the initial value is slightly lower than that of raw sand (1.88 μm²·cm), the overall performance is comparable. The static loss test shows that MRQS extends the filtration time of 200 mL filtrate to 439 s, which is 2.04 times that of the original sand. This simple dry coating strategy prepares a multifunctional support agent, which combines self-aggregation, temporary sealing, filter loss control and high stress stability, providing a practical solution to improve the fracturing performance of coal seam gas (CBM). Full article

Water in a coal seam matrix critically dictates the kinetic response and pore enhancement efficacy during liquid CO₂ displacement, yet the underlying mechanisms governing full-scale pore structure evolution under varying moisture regimes remain inadequately quantified. To address this issue, this study investigates the impact of the initial moisture content on pore damage in low-permeability anthracite. Low-field nuclear magnetic resonance and low-temperature nitrogen adsorption experiments were conducted. These techniques were combined to systematically evaluate the full-scale pore structure evolution before and after liquid CO₂ immersion. The results indicate that the specific surface area, total pore volume, and T₂ spectrum integral areas of microscopic pores at all scales exhibit a distinct non-linear, single-peak evolution pattern with increasing initial moisture content. The initial moisture content of 4.8% serves as a critical turning point for full-scale pore-space expansion and closure, at which the T₂ spectrum integral areas for micropores, mesopores, and macropores increase by 116.9%, 221.4%, and 243.5%, respectively, compared to the dry group, thereby effectively clearing blind-end pore throats; below this inflection point, moisture primarily mediates the carbonic acid dissolution response. Beyond this critical threshold, the mechanism transitions into a physical antagonism dominated by water-locking truncation and low-temperature frost-heaving damage. Compared to the 4.8% peak group, the T₂ spectrum integral areas for macropores, mesopores, and micropores in the 7.2% high-moisture group decrease significantly by 68.8%, 61.6%, and 46.1%, respectively, leading to an overall occlusion of full-scale pores. These findings provide crucial engineering guidance for field practices involving liquid CO₂ injection into moisture-bearing coal seams to enhance coalbed methane displacement. Full article