Abstract:Swelling is an effective method for improving coal properties and enhancing its utili-zation efficiency.In recent years,ionic liquids(ILs)have been employed as swelling agents for coal treatment.Although conventional ILs exhibit high stability and environmental friendli-ness,their low polarity limits their swelling efficiency.In contrast,halogen ionic liquids dem-onstrate stronger molecular polarity owing to the high polarity of halogen atoms.Therefore,three halogen-based ionic liquids([Bmim]Cl,[Bmim]Br,and[Bmim]I)were selectedto swell long-flame coal,aiming to investigate their effects on coal structural properties.The re-suits indicate that the swelling efficiency follows the order[Bmim]Cl＞[Bmim]Br＞[Bmim]I.The[Bmim]Cl-treated coal sample exhibited the highest swelling degree(25.07％)after 36 h of treatment at 25 ℃.Furthermore,swelling induced significant structural altera-tions in coal,including an increase in the interlayer spacing of aromatic clusters and a higher a-bundance of small molecular fragments on the coal surface.The oxygen content decreased,with a maximum reduction of 3.63％.Additionally,the weight loss rate of swollen coal sam-ples increased,and the pyrolysis temperature shifted toward lower ranges.Molecular simula-tions reveal that halogen ionic liquids weaken hydrogen bonds associated with oxygen-contai-ning functional groups,converting strong hydrogen bonds into weaker ones,with some bonds even breaking.These findings provide a theoretical foundation for improving coal pyrolysis and liquefaction efficiency,thereby facilitating the high-value utilization of coal resources.

Abstract:Sequestration of CO2 in deep coal seam is one of the most important ways for coal industry to energy saving and emission reduction.However,coal seams are heterogeneous porous media with pore size distributions ranging from nanometers to centimeters.In particular,the complex system of coal rock pores coexisting with multiple phases such as CO2,CH4,and H2O can generate various magnitude of capillary pressures,which will inevitably affect the injection of CO2 displacement and mass transfer.And therefore,the key issue in coalseam geological storage is how much pore and fracture space can be invaded and occupied by injecting CO2?In this regard,a pore network dynamic model was first established for CO2 invasion percolation in coal seam;Then,the pore network consis-ting of 90 pores on a coal sample scanned by an electron microscope(SEM)was taken as an example,a quantitative study was conducted regarding on the two continuous fluid dynamics processes of CO2 injection and reaching mechanical equilibrium after injection cessation.The results indicate that fluids such as CO2,CH4,and H2O in coal seam environments generate immiscible interfacial capillary re-sistance due to their immiscibility,the injected CO2 always chooses the path with the lowest resistance to move forward,resulting in CO2 only entering the pore and fracture spaces with larger pore diameter and lower resistance.The invasion percolation process of CO2 injection in coal seams is essentially a competition between the displacement pressure difference ΔP and the capillary resistance at the im-miscible interface,the larger the displacement pressure difference ΔP,the smaller the pore that can be entered,and the larger the effective space for CO2 sequestration.The flow process of CO2 injection in coal seam does not completely follow the commonly accepted Darcy flow,but exhibits multiple sta-ges of flow characteristics,in the initial stage of injection,CO2 can only enter the wetting pores and compete with CH4 in these pores for adsorption and desorption before reaching the non-wetting pore capillary entry pressure;Thereafter,CO2 follows the invasion percolation movement in non-wetting pores,and conforms to the Haynes jump unstable flow at wetting pores or pore intersection nodes;Later on,CO2 breaks through the coal seam pore and fracture network when reaching the threshold capillary breakthrough pressure,which means that injected CO2 has formed a continuous flow path in the coal seam and reached the coal seam outlet such as the production well,at this point,the flow mechanism begins to follow Darcy flow;Finally,if CO2 injection is stopped,wetting fluids such as water will undergo spontaneously imbibition,cutting off and closing the injected CO2 into two parts:structural storage and residual storage.This study has important implications for explaining the mechanisms behind engineering phenomena such as coal and gas outbursts,CO2 injection failure in porous media reservoirs such as shale and coal,and low efficiency of negative pressure gas extraction in coal mines.

Abstract:The flocculation and settling behavior of—30μm ultrafine hematite particles regula-ted by polyacrylamides(PAMs)of different ionic types was studied.A cross-scale response model of"interfacial adsorption-floc structure-settling performance"was established to reveal the multiscale mechanism by which molecular-level adsorption characteristics affect macroscop-ic settling behavior.Four types of PAMs-nonionic(NPAM),anionic(APAM),cationic(CPAM),and amphoteric(AmPAM)were evaluated.Zeta potential and adsorption density tests,Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),molecular dynamics simulation,and extended Derjaguin-Landau-Verwey-Overbeek(DLVO)theory were used to analyze differences in interfacial behavior,including adsorption energy and hydrogen bond formation.The results show that APAM has the strongest chain extension,most stable interfacial interaction,lowest adsorption energy,and the highest num-ber of hydrogen bonds.Based on focused beam reflectance measurement(FBRM),scanning e-lectron microscopy(SEM),fractal dimension,and porosity analyses,APAM-induced flocs ex-hibit an average chord length of 519.5 μm,a fractal dimension of 1.82,and a porosity of 38.9％,indicating the highest structural compactness.During settling,the APAM system shows a flocculation reaction time of 1.01 s,supernatant turbidity of 331 NTU,and floc con-centration of 51.9％,significantly outperforming the other systems.This study quantitatively clarifies the synergistic regulation mechanism of PAM ionic structures on hematite flocculation across molecular,mesoscopic,and macroscopic scales,providing theoretical support for floc-culant selection and process optimization in fine-particle slurry treatment.

Abstract:Methane in-situ deflagration fracturing technology creates complex fracture networks through high-temperature,high-pressure shock waves from the ignition of a mixture of reser-voir-desorbed methane and combustion-assisting agent.To investigate the characteristics of non-uniform mixed methane deflagration within the wellbore,a three-dimensional model for confined non-uniform methane deflagration was established.This model,based on a pre-charged agent delivery method,couples the Arrhenius kinetics with the eddy dissipation con-cept.The pressure characteristics of the wellbore deflagration were examined.The effects of wellbore pressure,temperature,methane volume fraction,and ignition method on the defla-gration pressure were analyzed.The results show that pre-charged injection creates distinct methane concentration zones along the wellbore.Centered at the injection tool,symmetrical regions are formed:low-concentration weak deflagration zones(5％—14％),intense deflagra-tion zones(15％—55％),and high-concentration weak deflagration zones(55％—92％)are formed.Compared to homogeneous combustion condition,heterogeneous mixing increases peak pressure at the wellbore bottom while reducing shock pressure at the upper sealed section by 12％—15％,establishing an optimized fracturing safety window.Parametric analysis indi-cates that increasing the initial pressure from 5 MPa to 15 MPa raises the peak deflagration pressure by 39.3 MPa,although the pressure rise rate decays with increasing pressure.At a constant initial pressure,every 40 K temperature increase causes a 10.4％attenuation in peak pressure.Heterogeneous mixing lowers the optimal methane combustion volume fraction from 33.3％to 26.8％,considerably reducing sensitivity to the mixing ratio.High-temperature ig-nition increases the peak pressure in the upper wellbore by 30％and effectively eliminates igni-tion delay observed in spark ignition systems.The findings reveal the deflagration enhance-ment effect under non-uniform mixing conditions and provide a theoretical basis for field appli-cations.

Abstract:To address the problem of gas extraction from soft and strongly adsorbed coal seams,the innovative idea of synergistic effect of high power ultrasonic field'mechanical vi-bration-cavitation-heat'to increase seepage and promote gas dissolution was adopted,and the research on the microscopic pore evolution and macroscopic desorption and diffusion behaviour of coal body under the excitation of ultrasonic field was carried out,and ultrasonic field seepage enhancement system device and the implementation of downhole long borehole seepage en-hancement process was developed.In addition,the engineering test of gas extraction was pro-moted by ultrasonic field excitatation of downhole along/through layer.The results indicate that after ultrasonic excitation,the maximum nitrogen adsorption capacities of Yuwu coal and Xintian coal increases from 2.314 0 and 1.661 6 cm3/g to 3.542 4 and 3.694 4 cm3/g,respec-tively,representing increases of 53.09％and 122.34％;the specific surface area is enhanced by 155.86％and 659.90％,respectively,and the pore volume increases by 66.67％and 100.00％.And the number of micropores and mesopores increases significantly and the pore struc-ture is effectively connected,which significantly improved the gas transport channels within the coal matrix.The result of gas adsorption and desorption experiments showes that the dif-fusion coefficients of the two coal samples increases from 1.76×10-8 and 8.95×10-8 m2/s to 1.99 ×10-8 and 1.05×10-7 m2/s,respectively,with an increase of 13.00％and 17.32％.The ultrasonic field excitation is sensitive to pore pressure,and the enhanced desorption effect is more significant in the low pore pressure stage.To adapt to the demand for seepage enhance-ment in soft and strongly adsorbed coal seams downhole,an 18 kW high-power ultrasonic field seepage enhancement system was developed,and a small-diameter,long borehole water-pres-sure synergistic ultrasonic segmentation seepage enhancement technology process was devel-oped.The results of the underground soft and strongly adsorbed coal seams ultrasonic seepage enhancement project tests show that after the ultrasonic excitation of the downhole borehole in the Yuwu Mine,the gas concentration increases by 101.82％～119.90％and the flow rate in-creases by 29.37％～136.72％in 30 d,and the radius of influence of the pumping promotion is up to 14 m.After ultrasonic infiltration enhancement in the hydraulic cavitation coal seam of Yuwu Coal Mine,the gas concentration increases by 5.14％～55.91％;after ultrasonic infil-tration enhancement in the penetrating borehole of Xintian Coal Mine,the gas concentration and flow rate increases by 58.35％～96.36％and 49.80％～54.57％respectively,and the ef-fective radius of pumping is more than 12 m,and the effective time of pumping is more than 60 d.In this study,microscopic,macroscopic and engineering multi-scale research were com-bined,the mechanism of ultrasonic field modified microscopic pore permeability enhancement and gas dissolution was elucidated,and the strengthening effect of pore water on ultrasonic pore expansion and permeability enhancement was revealed.This study confirms the good effect of ultrasonic field in the enhanced pumping of soft and strong adsorption coal seams,which provides an important support for the enhanced pumping of gas in soft and strongly ad-sorption coal seams.

Abstract:Surface subsidence in aeolian sand-covered coal mines represents a coupled failure mechanism involving bedrock subsidence and fluid-like response of overlying granular strata,where aeolian sand properties significantly influence surface deformation.To reveal the impact mechanism of aeolian sand thickness on bedrock-to-surface subsidence propagation under high-intensity mining in Shendong Coalfield,this study integrated field measurements,theoretical analysis,and numerical simulations to investigate subsidence propagation characteristics.A dual-medium subsidence propagation model was established based on physical-mechanical prop-erty contrasts and stress interactions between bedrock and aeolian sand,with a surface predic-tion formula derived from elastic foundation beam theory that accounts for both media under full extraction conditions.A novel block-particle coupled discrete element method was devel-oped to simulate dynamic bedrock-surface coupling deformation through cyclic stress transfer between bedrock damage patterns and basal stress redistribution in aeolian sand,thereby re-vealing subsidence propagation features and quantifying surface deformation under varying sand thicknesses.Field measurements show the relative surface settlement at the top of the bedrock is only 75-126 mm,indicating primary key stratum controlled synergistic subsidence propagation.As aeolian sand thickness increased from 9 m to 23 m,the surface subsidence fac-tor decreased by 6.45％-26.58％.Simulations further demonstrate that when sand thickness rose from 8 m to 40 m,the bedrock-to-surface subsidence attenuation escalated from 6.41％to 12.82％,confirming thicker sand layers retard subsidence propagation.In addition,the poros-ity of aeolian sand increased by an average of 0.085 3 before and after mining with different ae-olian sand thickness models,causing the subsidence space of the bedrock to dissipate in the voids of aeolian sand during the upward conduction process.Cross-validation among field data,simulations,and theoretical predictions verifies the reliability of both the numerical method and dual-medium prediction model.This research elucidates the dominant control behavior of bedrock under thin aeolian sand cover and the energy-dissipation buffering effect of thick sand layers,providing a scientific basis for surface deformation prediction and control in analogous mining areas.

Abstract:Deep mine roadways are susceptible to rockbursts due to high in-situ stresses and dy-namic disturbances from mining activities.To investigate the triggering mechanisms of rock-bursts undercoupled static-dynamic loads,a specialized physical simulation test system was developed.A unique gypsum-based model material,characterized by low strength,high brit-tleness,and excellent moldability,was formulated.This material was designed to accurately replicate the violent ejection of rock fragments characteristic of failures in deep roadways under combined static and dynamic loads.Comprising a main structural frame,a static loading de-vice,and a dynamic loading device,the system can simulate the complex stress conditions of"high static stress+dynamic disturbance"found in deep mining environments.The design ensures the stable application of static stress while preventing interference between the static and dynamic loading systems.Uniaxial compression tests on standard specimens revealed that the material has a uniaxial compressive strength of approximately 6.54 MPa and fails with a vi-olent ejection of fragments.This behavior confirms the material's strong bursting liability,making it suitable for physical modeling requirements.To enhance the fidelity of the simula-tion and bridge the gap between laboratory procedures and in-situ mining conditions,similarity principles were applied to the physical model's construction,scaling its dimensions,stress en-vironment,support materials,and other key parameters.Furthermore,a standardized work-flow and implementation protocol were established for conducting roadway rockburst simula-tions.Validation tests,using a case study of a kilometer-deep,fully-mechanized longwall top-coal caving roadway,were conducted.These tests analyzed the dynamic response characteris-tics of the surrounding rock mass and support structures under various cyclic impacts and sup-port conditions.The results confirmed the reliability of the test system,the model material,and the established methodology.This physical simulation platform effectively reproduces the complex static stress environment of deep roadways while allowing for the application of con-trolled dynamic disturbances.The platform is a valuable tool for investigating the deformation and failure mechanisms of rock masses under multi-field coupling,the triggering mechanisms of rockbursts from static-dynamic interactions,and for evaluating the efficacy of rockburst pre-vention technologies.

Abstract:Clay mineral transformation during deep burial of mudstone is closely related to mi-crostructure,physical properties and pore pressure,which was a major focus of mudstone compaction research.In this paper,the Mesozoic mudstone in the central Junggar Basin was selected as a research object,and based on the X-ray diffraction of clay minerals,the clay min-eral transformation process and its effect on the mudstone compaction behaviour and logging response were investigated.The results show that the clay minerals of the Mesozoic mudstone in the central Junggar Basin are mainly composed of mixed smectite-illite layer(mixed I/S lay-er)and illite,with a small amount of kaolinite and chlorite,and no discrete smectite.The Mesozoic mudstones underwent significant clay mineral transformation in a window with a depth of 4 000～4 800 m and a temperature of 90～105 ℃,with smectite in the mixed I/S layer being rapidly transformed into illite,as evidenced by a decrease in the smectite-to-illite ratio(I/S ratio)and a change in the mixing layer type from R0 to R3.According to the degree of clay mineral transformation,the compaction process of the mudstone was divided into three stages,and it was found that the pore reduction mechanism varied at different stages of com-paction.The effective stress was the main factor in pore reduction in the middle and shallow mechanical compaction stages,while the clay mineral transformation and the effective stress together intensified the loss of porosity in the deep mudstone.Clay mineral transformation leads to a decrease in mudstone porosity and an increase in density,which to some extent alters the response of different logging information to the compaction process,which leading to er-rors in the accurate identification of the compaction stage and the overpressure generation mechanisms.The improved sonic transit time-density cross plot,based on the normal compac-tion trend lines of different compaction stages,can be used to effectively differentiate the com-paction stages of deep mudstone and identify the overpressure generation mechanism.This study helps to deepen the theory of mudstone compaction and has important guiding value for predicting the pressure of deep layers.

Abstract:To elucidate the microscopic mechanisms underlying the conversion of coal to dia-mond and promote the clean and efficient utilization of coal resources,the processes of heteroa-tom removal,diamond nucleation,and diamond growth in coal were simulated using reactive force field molecular dynamics(ReaxFF MD).The results indicate a positive correlation be-tween pyrolysis temperature and the yield of both inorganic and organic gases.After three cy-cles of heteroatom removal at 4 000 K,the carbon content reached 98.54％for bituminous coal and 98.83％for anthracite.During the diamond nucleation stage,the minimum pressure(pmin)required for coal diamond nucleation negatively correlates with temperature and posi-tively correlates with the rate of pressure increase.The pmin of bituminous coal is higher than that of anthracite,and both coal types form hexagonal diamond nuclei.In the diamond growth stage,the diamond conversion rate increases with pressure.Elevated reaction temperature and reduced pressure increase rates significantly enhance the diamond conversion rate.At 4 000 K,with pressure elevated to 80.00 GPa at a rate of 0.05 GPa/ps,the diamond conversion rates reached 46.97％for bituminous coal and 45.77％for anthracite.Increasing the pressure to 80.00 GPa at 0.1 GPa/ps(4 000 K)and extending the time under constant temperature and pressure significantly improved the diamond conversion rate of bituminous coal.After 350 ps at constant temperature and pressure,the conversion rate increased from 29.68％to 53.65％for bituminous coal and from 21.32％to 31.27％for anthracite.Following diamond nuclea-tion,a transitional growth phase occurred,during which the conversion rates for both coal types gradually increased with pressure.During the high-temperature and high-pressure con-version process,mutual transformations between diamond and non-diamond structures oc-curred,as well as between cubic and hexagonal diamond structures.

Abstract:In light of the problems of cockamamie construction technology and high cost of constructing roadway existing in traditional gob-side entry retaining technology,an innovative no coal pillar mining technology by cutting roof to release pressure was proposed.Based on the movement laws of overlying strata in traditional gob-side entry retaining technology,the mechanism of pressure relief of gob-side roof was studied.In addition,several "surrounding rock structure-roadside support body" mechanical models were established considering different types of roof state,and the design formula of each roadway-side supporting resistance was obtained.The results show that the lower basic roof fall enough and then support the upper roof better by presplitting blasting,thereby limiting the rotational deformation of upper roof and reducing the impact load of roof break.The frature location of roof is shifted to the gob side,the length of the roof cantilever beam is reduced and the short cantilever beam is formed by roof cut,thus reducing the additional load of roadside support.Apart from that,some surrounding rock control technologies such as directional pre-splitting roof cutting technology,the constant resistance large deformation (CRLD) bolt and roadside intensive individual props were proposed.These technologies have been used in 12201 working face of Halagou coal mine and a good effect of field application was achieved.