There are various types of natural gas resources in coal measures,making them major targets for natural gas exploration and development in China.In view of the particularity of the whole petroleum system of coal measu...There are various types of natural gas resources in coal measures,making them major targets for natural gas exploration and development in China.In view of the particularity of the whole petroleum system of coal measures and the reservoir-forming evolution of natural gas in coal,this study reveals the formation,enrichment characteristics and distribution laws of coal-rock gas by systematically reviewing the main types and geological characteristics of natural gas in the whole petroleum system of coal measures.First,natural gas in the whole petroleum system of coal measures is divided into two types,conventional gas and unconventional gas,according to its occurrence characteristics and accumulation mechanism,and into six types,distal detrital rock gas,special rock gas,distal/proximal tight sandstone gas,inner-source tight sandstone gas,shale gas,and coal-rock gas,according to its source and reservoir lithology.The natural gas present in coal-rock reservoirs is collectively referred to as coal-rock gas.Existing data indicate significant differences in the geological characteristics of coal-rock gas exploration and development between shallow and deep layers in the same area,with the transition depth boundary generally 1500-2000 m.Based on the current understanding of coal-rock gas and respecting the historical usage conventions of coalbed methane terminology,coal-rock gas can be divided into deep coal-rock gas and shallow coalbed methane according to burial depth.Second,according to the research concept of“full-process reservoir formation”in the theory of the whole petroleum system of coal measures,based on the formation and evolution of typical coal-rock gas reservoirs,coal-rock gas is further divided into four types:primary coal-rock gas,regenerated coal-rock gas,residual coal-rock gas,and bio coal-rock gas.The first two belong to deep coal-rock gas,while the latter two belong to shallow coal-rock gas.Third,research on the coal-rock gas reservoir formation and evolution shows that shallow coal-rock gas is mainly residual coal-rock gas or bio coal-rock gas formed after geological transformation of primary coal-rock gas,with the reservoir characteristics such as low reservoir pressure,low gas saturation,adsorbed gas in dominance,and gas production by drainage and depressurization,while deep coal-rock gas is mainly primary coal-rock gas and regenerated coal-rock gas,with the reservoir characteristics such as high reservoir pressure,high gas saturation,abundant free gas,and no or little water.In particular,the primary coal-rock gas is wide in distribution,large in resource quantity,and good in reservoir quality,making it the most favorable type of coal-rock gas for exploration and development.展开更多
Coal measures are significant hydrocarbon source rocks and reservoirs in petroliferous basins.Many large gas fields and coalbed methane fields globally are originated from coal-measure source rocks or accumulated in c...Coal measures are significant hydrocarbon source rocks and reservoirs in petroliferous basins.Many large gas fields and coalbed methane fields globally are originated from coal-measure source rocks or accumulated in coal rocks.Inspired by the discovery of shale oil and gas,and guided by“the overall exploration concept of considering coal rock as reservoir”,breakthroughs in the exploration and development of coal-rock gas have been achieved in deep coal seams with favorable preservation conditions,thereby opening up a new development frontier for the unconventional gas in coal-rock reservoirs.Based on the data from exploration and development practices,a systematic study on the accumulation mechanism of coal-rock gas has been conducted.The mechanisms of“three fields”controlling coal-rock gas accumulation are revealed.It is confirmed that the coal-rock gas is different from CBM in accumulation process.The whole petroleum systems in the Carboniferous–Permian transitional facies coal measures of the eastern margin of the Ordos Basin and in the Jurassic continental facies coal measures of the Junggar Basin are characterized,and the key research directions for further developing the whole petroleum system theory of coal measures are proposed.Coal rocks,compared to shale,possess intense hydrocarbon generation potential,strong adsorption capacity,dual-medium reservoir properties,and partial or weak oil and gas self-sealing capacity.Additionally,unlike other unconventional gas such as shale gas and tight gas,coal-rock gas exhibits more complex accumulation characteristics,and its accumulation requires a certain coal-rock play form lithological and structural traps.Coal-rock gas also has the characteristics of conventional fractured gas reservoirs.Compared with the basic theory and model of the whole petroleum system established based on detrital rock formations,coal measures have distinct characteristics and differences in coal-rock reservoirs and source-reservoir coupling.The whole petroleum system of coal measures is composed of various types of coal-measure hydrocarbon plays with coal(and dark shale)in coal measures as source rock and reservoir,and with adjacent tight layers as reservoirs or cap or transport layers.Under the action of source-reservoir coupling,coal-rock gas is accumulated in coal-rock reservoirs with good preservation conditions,tight oil/gas is accumulated in tight layers,conventional oil/gas is accumulated in traps far away from sources,and coalbed methane is accumulated in coal-rock reservoirs damaged by later geological processes.The proposed whole petroleum system of coal measures represents a novel type of whole petroleum system.展开更多
In the gas-coal integrated mining field,the conventional design method of pipeline coal pillars leads to a large amount of coal pillars being unrecovered and overlooks the pipeline's safety requirements.Considerin...In the gas-coal integrated mining field,the conventional design method of pipeline coal pillars leads to a large amount of coal pillars being unrecovered and overlooks the pipeline's safety requirements.Considering the coal pillar recovery rate and pipeline's safety requirements,two new shaped coal pillar design approaches for subsurface pipelines were developed.Firstly,the deformation limitations for measuring pipeline safety are categorized into two:no deformation is permitted,and deformation is acceptable within elastic limits.Subsequently,integrating the key stratum theory(KST)and cave angle,a fishbone-shaped coal pillar design approach that does not permit pipeline deformation is established.Meanwhile,combined with the ground subsidence and the pipeline's elastic deformation limit,a grille-shaped coal pillar design approach that accepts deformation pipelines within elastic limits is established.Those two new approaches clarify parameters including mined width,coal pillar width and mined length.Finally,the case study shows that the designed mined width,coal pillar width and mined length of the fishbone-shaped coal pillar are 90,80,and 130 m,while those of the grille-shaped are 320,370,and640 m.Compared with the conventional method,the fishbone-shaped and grille-shaped coal pillar design approaches recovered coal pillar resources of 2.65×10~6and 5.81×10~6t on the premise of meeting the pipeline safety requirements,and the recovery rates increased by 20.5%and 45.0%,with expenditures representing only 56.46%and 20.02%of the respective benefits.These new approaches provide managers with diverse options for protecting pipeline safety while promoting coal pillar recovery,which is conducive to the harmonic mining of gas-coal resources.展开更多
Based on the coalbed methane(CBM)/coal-rock gas(CRG)geological,geophysical,and experimental testing data from the Daji block in the Ordos Basin,the coal-forming and hydrocarbon generation&accumulation characterist...Based on the coalbed methane(CBM)/coal-rock gas(CRG)geological,geophysical,and experimental testing data from the Daji block in the Ordos Basin,the coal-forming and hydrocarbon generation&accumulation characteristics across different zones were dissected,and the key factors controlling the differential CBM/CRG enrichment were identified.The No.8 coal seam of the Carboniferous Benxi Formation in the Daji block is 8-10 m thick,typically overlain by limestone.The primary hydrocarbon generation phase occurred during the Early Cretaceous.Based on the differences in tectonic evolution and CRG occurrence,and with the maximum vitrinite reflectance of 2.0%and burial depth of 1800 m as boundaries,the study area is divided into deeply buried and deeply preserved,deeply buried and shallowly preserved,and shallowly buried and shallowly preserved zones.The deeply buried and deeply preserved zone contains gas content of 22-35 m^(3)/t,adsorbed gas saturation of 95%-100%,and formation water with total dissolved solid(TDS)higher than 50000 mg/L.This zone features structural stability and strong sealing capacity,with high gas production rates.The deeply buried and shallowly preserved zone contains gas content of 16-20 m^(3)/t,adsorbed gas saturation of 80%-95%,and formation water with TDS of 5000-50000 mg/L.This zone exhibits localized structural modification and hydrodynamic sealing,with moderate gas production rate.The shallowly buried and shallowly preserved zone contains gas content of 8-16 m^(3)/t,adsorbed gas saturation of 50%-70%,and formation water with TDS lower than 5000 mg/L.This zone experienced intense uplift,resulting in poor sealing and secondary alteration of the primary gas reservoir,with partial adsorbed gas loss,and low gas production rate.A depositional unification and structural divergence model is proposed,that is,although coal seams across the basin experienced broadly similar depositional and tectonic histories,differences in tectonic intensity have led to spatial heterogeneity in the maximum burial depth(i.e.,thermal maturity of coal)and current burial depth and occurrence of CRG(i.e.,gas content and occurrence state).The research results provide valuable guidance for advancing the theoretical understanding of CBM/CRG enrichment and for improving exploration and development practices.展开更多
As an important pillar of China's industrialization process,the coal industry has not only made contributions to economic growth,but also left a large number of coal mine sites bearing historical memories.These si...As an important pillar of China's industrialization process,the coal industry has not only made contributions to economic growth,but also left a large number of coal mine sites bearing historical memories.These sites are not only the witness of the industrial civilization,but also the potential resources for urban renewal and industrial transformation.展开更多
Deep mining is imperative,and the consequent coal and gas outburst disasters triggered during coal uncovering are becoming increasingly severe.Therefore,this study investigated the mechanical mechanisms of outburst in...Deep mining is imperative,and the consequent coal and gas outburst disasters triggered during coal uncovering are becoming increasingly severe.Therefore,this study investigated the mechanical mechanisms of outburst instability from three dimensions:experiment,numerical simulation,and field application.Based on physical simulation tests with different outburst pore diameter,it was found that the gas pressure relief rate,gas emission volume,and outburst dynamic phenomena increase with outburst pore diameter.The migration patterns of the gas-solid two-phase flow evolved over time approximately into suspension flow,plug flow,dune flow,and stratified flow.The dominant influence of gas-driven tensile failure was amplified by uncovering coal area.The employment of the“fluid-solid-damage”coupling model revealed that coal damage,gas emission volume,deflection angle of outburst hole,roof displacement,maximum horizontal tensile stress,the horizontal tensile stress zone,the peak seepage force,and the damage zone all increased with uncovering coal areas.At the gas pressure of 0.74 MPa,when the uncovering coal areas were 3.189,4.754 and 6.225 m,the total gas emission volumes were 4.72×10^(-4),16.83×10^(-4),and 17.67 m^(2)/s,deflection angles of outburst hole were 150.79°,152.89°and 158.66°,the maximum roof displacements were 0.044,0.046,and 0.325 m,and the peak seepage force were 0.85,1.27,and 1.46 MPa/m,respectively.The regions of coal failure calculated by tensile failure criterion largely coincided with those calculated by the mixed failure criterion,far greater than those calculated by the shear failure criterion.As the increase of uncovering coal area,tensile weights of 80.72%,89.78%,and 93.01%,respectively.Comparisons with field outburst cases showed that both gas emission volume and outburst hole deflection angle reflected the tensile failure of coal.The mechanical instability process of outbursts under the influence of uncovering coal area and gas pressure was analyzed,developing the progressive cyclical method of coal uncovering,which provided a novel approach for the achievement of safe coal mining.展开更多
To address issues such as inefficient top-coal drawing,challenges in simultaneously mining and drawing,and the need for intelligent control in extra-thick coal seams,this study examines the principles of top-coal draw...To address issues such as inefficient top-coal drawing,challenges in simultaneously mining and drawing,and the need for intelligent control in extra-thick coal seams,this study examines the principles of top-coal drawing and explores automation and intelligent equipment solutions within the framework of the group coal drawing method.Numerical simulations were performed to investigate the impact of the Number of Drawing Openings(NDO)and rounds on top-coal recovery,coal draw-ing efficiency,and Top Coal Loss(TCL)mechanism.Subsequently,considering the recovery and coal drawing efficiency and by introducing the instantaneous gangue content and cumulative gangue content in simulations,the top-coal recovery,gangue content,and coal loss distribution when considering excessive coal drawing were analyzed.This established a foun-dation for determining the optimal NDO and shutdown timing.Finally,the key technical principle and automated control of a shock vibration and hyperspectral fusion recognition device were detailed,and an intelligent coal drawing control method based on this technology was developed.This technology enabled the precise control of the instantaneous gangue content(35%)during coal drawing.The top-coal recovery at the Tashan Mine 8222 working face increased by 14.78%,and the gangue content was controlled at~9%,consistent with the numerical simulation results.Thus,the reliability of the numerical simulation results was confirmed to a certain extent.Meanwhile,the single-group drawing method significantly enhanced the production capacity of the 8222 working face,achieving an annual output of 15 million tons.展开更多
This review details the state of the art in research on top coal drawing mechanisms in Longwall top coal caving(LTCC)by examining the relevant literature over the last two decades.It startswith an introduction of the ...This review details the state of the art in research on top coal drawing mechanisms in Longwall top coal caving(LTCC)by examining the relevant literature over the last two decades.It startswith an introduction of the brief history and basic procedures of LTCC.The framework of research on the drawing mechanism,basic concepts,and some theoretical models of LTCC are detailed in sect.research framework of top coal drawingmechanism.The authors note that theTop coal drawbody(TCD),Top coal boundary(TCB)and Top coal recovery ratio(TCRR)are key factors in the drawingmechanism.TheBody-boundary-ratio(BBR)research system has been the classic framework for research over the last 20 years.The modified Bergmark-Roos model,which considers the effects of the supporting rear canopy,flowing velocity of top coal,and its shape factor,is optimal for characterizing the TCD.A 3Dmodel to describe the TCB that considers the thicknesses of the coal seam and roof strata is reviewed.In sect.physical testing and numerical simulation,the physical tests and numerical simulations in the literature are classified for ease of bibliographical review,and classic conclusions regarding the drawing mechanism of top coal are presented and discussedwith elaborate illustrations and descriptions.The deflection of the TCDis noted,and is caused by the shape of the rear canopy.The inclined coal seam always induces a largerTCD,and a deflection in theTCDhas also been observed in it.The effects of the drawing sequence and drawing interval on the TCRR are reviewed,where a long drawing interval is found to lead to significant loss of top coal.Its flowing behavior and velocity distribution are also presented.Sect.practical applications of drawingmechanisms forLTCCmines 4 summarizes over 10 cases where the TCRRof LTCCmines improved due to the guidance of the drawing mechanism.The final section provides a summary of the work here and some open questions.Prospective investigations are highlighted to give researchers guidance on promising issues in future research on LTCC.展开更多
In this study,to better decide the effect of coal seam dip angle upon the dynamic change of the crossfusion in gas transport and storage areas during the progress of working face in the high gas thick coal seam,a two-...In this study,to better decide the effect of coal seam dip angle upon the dynamic change of the crossfusion in gas transport and storage areas during the progress of working face in the high gas thick coal seam,a two-dimensional physical simulation experiment regarded as the theoretical research was conducted to properly explore the variation law of overburden fracture.The results demonstrated that the boundary of the gas transport zone was located in the region of fracture separation.The boundary of the gas storage area was located in the abrupt penetration zone.Also,according to the information theory,the state of the gas transport and storage areas was determined by the changing trend of the fracture rate and fracture entropy.The mathematical representation model of the dip effect in gas transport and storage areas was established.The criteria upon which the regional location of the gas transport area and gas storage area can be based were put forward.The cross-fusion evolution process of the dip effect in gas transport and storage areas was revealed as well.The research results could provide guidance for realising directional and accurate gas extraction.展开更多
The occurrence of coal-bearing strata in a variety of coal-bearing basins of China is characterized by late tectonic deformation and remarkable spatial and geochronologic differences.The main controlling factors,which...The occurrence of coal-bearing strata in a variety of coal-bearing basins of China is characterized by late tectonic deformation and remarkable spatial and geochronologic differences.The main controlling factors,which determine the tectonic framework of coalfields,include the geodynamic environment,tectonic evolution,deep structures,tectonic stress,and lithologic combination of the coal measures.The Chinese continent has experienced multi-stage tectonic movements since the Late Paleozoic.The spatial and temporal heterogeneity of its continental tectonic evolution,the complexity of its basement properties,and its stratigraphic configurations control the tectonic framework of its coalfields’present complex and orderly patterns.The concept of coal occurrence structural units is proposed in this paper and is defined as the structural zoning of coal occurrence.China’s coalfields are divided into five coal occurrence structural areas,and the structural characteristics of the coalfields in five main coal occurrence areas throughout the country are summarized.Based on the analysis of the relationship between the structure characteristics and occurrence of coal in these coalfields,the coal-controlling structures are divided into six groups:extensional structural styles,compressional structural styles,shearing and rotational structural styles,inverted structural styles,sliding structural styles,and syn-depositional structural styles.In addition,the distribution of coal-controlling structural styles is briefly summarized in this paper.展开更多
The hydraulic fractures induced in soft coal composite reservoirs have complex extension and energy evolution characteristics.In this study,the mechanism whereby gas outbursts can be eliminated by hydraulic fracturing...The hydraulic fractures induced in soft coal composite reservoirs have complex extension and energy evolution characteristics.In this study,the mechanism whereby gas outbursts can be eliminated by hydraulic fracturing was revealed.The combined fracturing process of a coal seam and its roof under different in situ stress and fracture spacing conditions was analysed through true triaxial physical tests and numerical simulations.The results showed that the pre-fracturing of the roof had a pressure relief effect on the coal seam,and the secondary pressure relief of the coal seam could be completed at a lower fracture initiation pressure.To ensure the continued presence of the stress shadow effect in actual projects,the fracture spacing should be maintained within the critical range influencing the fracture extension.If the vertical stress is high,a call on increasing the fracture spacing can be taken;otherwise,it must be reduced.In the early phase of fracturing,energy is mostly concentrated at the tip and surface of the fracture;however,the proportion of surface energy for subsequent fracturing is gradually reduced,and the energy is mostly used to open the formation and work on the surrounding matrix.Hydraulic fracturing creates new fractures to interconnect originally heterogeneously distributed gas zones,enabling the entire coal seam to first establish interconnected pressure equilibration,then undergo gradientcontrolled depressurization.Hydraulic fracturing can homogenize the stress field and gas pressure field in the original coal seam via communication pressure equalization and reduction decompression,reduce the elastic and extension energies,increase the minimum failure energy required for instability;and realize the elimination of gas outbursts.Our findings provide some theoretical support for the efficient development of coalbed methane and the prevention and control of dynamic gas disasters in coal mines.展开更多
It is important to understand the effects of demineralization on the reactivity of coal pyrolysis for demineralization coal in OCCSS systems.The molecular dynamics of the pyrolysis of ZD-R and ZD-D was investigated us...It is important to understand the effects of demineralization on the reactivity of coal pyrolysis for demineralization coal in OCCSS systems.The molecular dynamics of the pyrolysis of ZD-R and ZD-D was investigated using the ReaxFF MD method.It is indicated that the pyrolysis reactivity of ZD-D is enhanced.Acid demineralization treatment helps to enhance the cross-linking reaction of light tar C5-14 molecules in the main pyrolysis stage,generating light tar fragments with higher molecular mass.In the polycondensation pyrolysis stage,the acid demineralization treatment promotes the polycondensation reaction at high temperatures.The generation of H2 in ZD-R pyrolysis is primarily attributed to the N-H bond breaking in pyrrole at low temperatures.At high temperatures,it is predominantly associated with the hydrogen abstraction reaction between carboxyl functional groups and the dehydrogenation reaction of hydrogen bond breaking in the aliphatic hydrocarbon structures.H2O is primarily attributed to the reaction of the hydroxyl group on the carboxyl group.CO_(2) is always related to the carboxyl group.CO is mainly related to the reduction reaction of carbonyl group,carboxyl group,and CO_(2).During the initial pyrolysis stage of ZD-D after acid demineralization treatment,the hydrogen abstraction reaction of the carboxyl functional group and the generation of CO molecules by the methoxy group are enhanced.The generation of H2 by the aliphatic structure is enhanced in the main pyrolysis stage.The ring-opening reaction of the phenoxy group to generate CO in the polycondensation pyrolysis stage is also facilitated.展开更多
China has abundant resources of high-alumina coal(HAC).However,its application as a raw gasification material is limited owing to high ash-fusion characteristics.For overcoming the limitation,this study employed Xinji...China has abundant resources of high-alumina coal(HAC).However,its application as a raw gasification material is limited owing to high ash-fusion characteristics.For overcoming the limitation,this study employed Xinjiang coal(XJ),having a low ash fusion temperature,to improve the ash fusibility and viscosity of high-alumina Jungar coal(JG).The evolution of Al-containing phases and structures during mixed ash melting were investigated based on XRD,XPS,27Al NMR,high-temperature stage microscopy(HTSM),and thermodynamic simulations.An increase in the XJ mass ratio resulted in the transformation of gehlenite to anorthite and mullite,producing more amorphous materials at high temperature.These phenomena were manifested at a microscopic imaging as an increase in the number of reaction/melting sites and their area expansion rate,as well as a decrease in ash area shrinkage and melting temperature.Moreover,the introduction of XJ altered the alumina-oxygen network,reducing the binding to the silicaoxygen network and converting some[AlO_(6)]^(9-)to[AlO_(4)]^(5-)as the relative concentration of O_(2)-and O-increases.Consequently,the decrease in the stability of the aluminate structure improves the AFT and viscosity.Based on these results,a mechanism to improve the ash fusion characteristics of HAC based on coal blending is proposed.展开更多
Coal pillars are critical supporting structures between underground coal gasification gasifiers.Its bearing capacity and structural stability are severely threatened by high-temperature environments.To elucidate the h...Coal pillars are critical supporting structures between underground coal gasification gasifiers.Its bearing capacity and structural stability are severely threatened by high-temperature environments.To elucidate the high-temperature deterioration mechanism of coal pillars at multiple scales,coal strength features as a function of temperature were investigated via uniaxial compression and acoustic emission equipment.The pyrolysis reaction process and microstructure evolution were characterized via X-ray diffractometer(XRD),scanning electron microscope(SEM),thermogravimetric(TG),Fourier transform infrared spectroscopy(FTIR),and computed tomography(CT)tests.Experimental results reveal a critical temperature threshold of 500℃for severe degradation of the coal bearing capacity.Specifically,both the strength and elastic modulus exhibit accelerated degradation above this temperature,with maximum reductions of 45.53%and 61.34%,respectively.Above 500℃,coal essentially undergoes a pyrolysis reaction under N_(2)and CO_(2)atmospheres.High temperatures decrease the quantity of O_(2)-based functional groups,growing aromaticity and the degree of graphitization.These changes induce dislocation and slip inside the coal crystal nucleus and then lead to deformation of the coal molecular structural units and strain energy generation.This process results in a great increase in porosity.Consequently,the stress deformation of coal increases,transforming the type of failure from brittle to ductile failure.These findings are expected to provide scientific support for UCG rock strata control.展开更多
Physical analog modeling is an effective approach for studying the hazards of coal bursts in coal similarity criteria for physical and mechanical parameters of the actual and similar materials are crucial to yield rea...Physical analog modeling is an effective approach for studying the hazards of coal bursts in coal similarity criteria for physical and mechanical parameters of the actual and similar materials are crucial to yield realistic results.The derivation of similarity criteria is predominantly based on dimensional analysis,while a systematic methodology has yet to be developed.This paper attempts to fill this gap by combining the equation transformation method with similarity theory to conduct an in-depth study on the similarity criteria of physical parameters of impact coal with various internal block sizes.On this basis,the influence of internal block size of impact coal on similarity criteria was studied.Block size can provide a selection basis for similar materials,and the influence of block size on model physical parameters and similarity criteria under different geometric similarity ratios was explored.The variation laws between geometric similarity ratio,block size,and physical properties were clarified,and the similarity criteria of impact coal under the influence of block size were adjusted.New insights into material selection for physical analog modeling were proposed.The established similarity criteria for impact coal under the influence of different block sizes can provide a theoretical basis for determining various parameters in the physical analog modeling of coal bursts,when building a physical model of impact coal,material selection and size selection can be based on similarity criteria to more accurately reproduce coal explosion disasters in the laboratory.展开更多
Gas channeling in fractures during CO_(2) injection into the deep coal seam seriously reduces the CO_(2) storage efficiency after the development of coalbed methane.The generation and migration of coal fines causes bl...Gas channeling in fractures during CO_(2) injection into the deep coal seam seriously reduces the CO_(2) storage efficiency after the development of coalbed methane.The generation and migration of coal fines causes blockages in the fractures in the stage of drainage and gas production,reducing the gas channeling effect of injected CO_(2) caused by the heterogeneity of the coal seam.To explore the impact of coal fines within coal seam fractures on the efficacy of CO_(2) storage,experiments on the production stage and CO_(2) injection for storage were conducted on coal combinations containing propped fractures,fractures,and matrix.The CO_(2) storage characteristics of coal at the constraint of coal fines,as well as the influence of multiple rounds of intermittent CO_(2) injection and different injection parameters on the CO_(2) storage effect,were analyzed.The research results show that blockage by coal fines increases the resistance to fluid flow in the fractures by 71.2%.The CO_(2) storage capacity and storage potential of coal with coal fines are 6.5 cm^(3)/g and 8.8%higher than those of coal without coal fines,while the CO_(2) storage capacity of fractured coal under the influence of coal fines has the largest increase of 9.4 cm^(3)/g.The CO_(2) storage of coal containing coal fines is significantly higher(6.6%)than that of the coal without coal fines.The CO_(2) storage effect of the coal with coal fines is improved with the increase in injection rate,whereas the CO_(2) storage effect of the coal without coal fines decreases significantly(by 7.8%).Multiple rounds of intermittent injection increases the CO_(2) storage volume of coal by 20.4%(with coal fines)and 17.1%(without coal fines).The presence of coal fines in fractures also slows down the downward trend of CO_(2) storage fraction after multiple rounds of CO_(2) injection.The blockage in fractures significantly increases the CO_(2) injection time and difficulty,but can increase the CO_(2) storage fraction by 4.7%-17.1%,and the storage volume by 1.9%-14%,increasing the feasibility of CO_(2) storage in fractured coal seams that have previously been exploited for methane production.The multiple rounds of intermittent CO_(2) injection and shut-in periods has shown potential for greater CO_(2) storage and injection efficiency.展开更多
On 30 September 2024,the UK shuttered its last remaining coal-fired power plant[1].The closure marks a historic milestone,the end of 142 years of coal fueled prosperity.The country opened the world’s first plant to s...On 30 September 2024,the UK shuttered its last remaining coal-fired power plant[1].The closure marks a historic milestone,the end of 142 years of coal fueled prosperity.The country opened the world’s first plant to supply electric streetlamps in 1882,spark-ing a global energy revolution that has led to today’s nearly univer-sally electrified world.展开更多
The issue of top contact in paste backfill materials is a common technical challenge in coal mine filling processes,and overcoming this problem has become a significant research direction in current studies and engine...The issue of top contact in paste backfill materials is a common technical challenge in coal mine filling processes,and overcoming this problem has become a significant research direction in current studies and engineering practices.This paper utilizes coal gangue as aggregate and hydrogen peroxide as a foaming agent to prepare foamed paste backfill materials.Three close-packing theories were employed to investigate the effects of different coal gangue particle gradations on the mechanical properties,expansion ratio,water absorption,and dry density of foamed paste backfill materials under the same foaming agent content.The hydration mechanism and pore structure evolution were analyzed using XRD,SEM,and OSM techniques.The results indicate that when the hydrogen peroxide addition is 5%,the foamed paste backfill material regulated by MAA gradation theory exhibits the best comprehensive performance,achieving a 28-day compressive strength of 0.89 MPa,an expansion ratio of 155.5%,and a dry density of 1.24 g/cm^(3).The regulation of coal gangue aggregate particle gradation not only improves the foaming efficiency but also allows the formation of CH to fill the material pores,enhancing the overall structural support capacity and forming a closer microstructure.This research provides new insights into controlling the properties of foamed paste backfill materials.展开更多
In extremely close-distance coal seam(ECDCS)mining,section coal pillars remain after upper coal seam(UCS)extraction.Thus,for layout and support design of lower coal seam(LCS)mining roadways,it is critical to account f...In extremely close-distance coal seam(ECDCS)mining,section coal pillars remain after upper coal seam(UCS)extraction.Thus,for layout and support design of lower coal seam(LCS)mining roadways,it is critical to account for UCS goaf deterioration and residual coal pillar(RCP)-induced stress disturbance.Taking the 6.4 m layer spacing of ECDCS mining in Nanyangpo Coal Mine as a case study,this research aimed to determine the optimal layout and surrounding rock control method for the 24202-ventilation roadway in the RCP area.First,the challenges of roadway layout and support under RCP were clarified:three layout methods face distinct RCPinduced stress disturbances and goaf-related roof damage.A finite element model was established;the second invariant of deviatoric stress(J_(2))and horizontal stress index were introduced to analyze plastic zone and stress evolution after UCS mining.Results show that J_(2)distributes symmetrically,with its peak diffusing downward and attenuating in a“/”-shaped pattern.Six schemes were simulated to compare plastic zone distributions at different positions,revealing that the optimal layout consists of a roadway alignment with the RCP center.Based on roadway layout and roof conditions,a cooperative control scheme was proposed:deep,strong anchorage with long cables across the RCP,and shallow stable support with short bolts in the ECDCS.This scheme secures roof cables anchored to the UCS RCP roof to achieve cross-seam anchorage.On-site borehole peeping and loose circle tests confirm smooth surrounding rock hole walls and limited failure range.Specifically,surrounding rock deformation and roof separation were controlled within 200 mm and 80 mm,respectively,with stable bolt/cable support resistance.These results offer an innovative solution for roadway layout design and support strategies under RCP in ECDCS,with significant engineering application value.展开更多
Coal bursts pose significant safety and operational challenges in deep mining environments,necessitating effective mitigation strategies to address high-stress concentrations and dynamic failure risks.This study evalu...Coal bursts pose significant safety and operational challenges in deep mining environments,necessitating effective mitigation strategies to address high-stress concentrations and dynamic failure risks.This study evaluated the efficacy of hydraulic fracturing as a preconditioning tool at a longwall face of the Mengcun coal mine with strong coal bursts,Shaanxi Province.The program involved the systematic creation of a fracture network through high-pressure fluid injection,monitored via microseismic arrays,stress measurements,and hydrological sensors.Results demonstrated that hydraulic fracturing effectively redistributed in-situ stresses,reducing high-stress concentrations by up to 30%,lowering the frequency of high-energy microseismic events,and enhancing the stability of fractured zones.However,the presence of unfractured blind spots and interactions with pre-existing faults highlighted the need for optimized well placement and adaptive fracturing designs.These findings underscore the potential of hydraulic fracturing as a critical preconditioning tool in high-stress mining operations,which could provide a framework for improving safety and efficiency in similar geological and operational settings.展开更多
基金Supported by the National Science and Technology Major Project for New Oil and Gas Exploration and Development(2025ZD1404200)Forward-looking and Fundamental Project of PetroChina Company Limited(2024DJ23)Scientific Research and Technology Development Project of PetroChina Research Institute of Petroleum Exploration&Development(2024vzz).
文摘There are various types of natural gas resources in coal measures,making them major targets for natural gas exploration and development in China.In view of the particularity of the whole petroleum system of coal measures and the reservoir-forming evolution of natural gas in coal,this study reveals the formation,enrichment characteristics and distribution laws of coal-rock gas by systematically reviewing the main types and geological characteristics of natural gas in the whole petroleum system of coal measures.First,natural gas in the whole petroleum system of coal measures is divided into two types,conventional gas and unconventional gas,according to its occurrence characteristics and accumulation mechanism,and into six types,distal detrital rock gas,special rock gas,distal/proximal tight sandstone gas,inner-source tight sandstone gas,shale gas,and coal-rock gas,according to its source and reservoir lithology.The natural gas present in coal-rock reservoirs is collectively referred to as coal-rock gas.Existing data indicate significant differences in the geological characteristics of coal-rock gas exploration and development between shallow and deep layers in the same area,with the transition depth boundary generally 1500-2000 m.Based on the current understanding of coal-rock gas and respecting the historical usage conventions of coalbed methane terminology,coal-rock gas can be divided into deep coal-rock gas and shallow coalbed methane according to burial depth.Second,according to the research concept of“full-process reservoir formation”in the theory of the whole petroleum system of coal measures,based on the formation and evolution of typical coal-rock gas reservoirs,coal-rock gas is further divided into four types:primary coal-rock gas,regenerated coal-rock gas,residual coal-rock gas,and bio coal-rock gas.The first two belong to deep coal-rock gas,while the latter two belong to shallow coal-rock gas.Third,research on the coal-rock gas reservoir formation and evolution shows that shallow coal-rock gas is mainly residual coal-rock gas or bio coal-rock gas formed after geological transformation of primary coal-rock gas,with the reservoir characteristics such as low reservoir pressure,low gas saturation,adsorbed gas in dominance,and gas production by drainage and depressurization,while deep coal-rock gas is mainly primary coal-rock gas and regenerated coal-rock gas,with the reservoir characteristics such as high reservoir pressure,high gas saturation,abundant free gas,and no or little water.In particular,the primary coal-rock gas is wide in distribution,large in resource quantity,and good in reservoir quality,making it the most favorable type of coal-rock gas for exploration and development.
基金Supported by the PetroChina Basic Project(2024DJ23)CNPC Science Research and Technology Development Project(2021DJ0101)。
文摘Coal measures are significant hydrocarbon source rocks and reservoirs in petroliferous basins.Many large gas fields and coalbed methane fields globally are originated from coal-measure source rocks or accumulated in coal rocks.Inspired by the discovery of shale oil and gas,and guided by“the overall exploration concept of considering coal rock as reservoir”,breakthroughs in the exploration and development of coal-rock gas have been achieved in deep coal seams with favorable preservation conditions,thereby opening up a new development frontier for the unconventional gas in coal-rock reservoirs.Based on the data from exploration and development practices,a systematic study on the accumulation mechanism of coal-rock gas has been conducted.The mechanisms of“three fields”controlling coal-rock gas accumulation are revealed.It is confirmed that the coal-rock gas is different from CBM in accumulation process.The whole petroleum systems in the Carboniferous–Permian transitional facies coal measures of the eastern margin of the Ordos Basin and in the Jurassic continental facies coal measures of the Junggar Basin are characterized,and the key research directions for further developing the whole petroleum system theory of coal measures are proposed.Coal rocks,compared to shale,possess intense hydrocarbon generation potential,strong adsorption capacity,dual-medium reservoir properties,and partial or weak oil and gas self-sealing capacity.Additionally,unlike other unconventional gas such as shale gas and tight gas,coal-rock gas exhibits more complex accumulation characteristics,and its accumulation requires a certain coal-rock play form lithological and structural traps.Coal-rock gas also has the characteristics of conventional fractured gas reservoirs.Compared with the basic theory and model of the whole petroleum system established based on detrital rock formations,coal measures have distinct characteristics and differences in coal-rock reservoirs and source-reservoir coupling.The whole petroleum system of coal measures is composed of various types of coal-measure hydrocarbon plays with coal(and dark shale)in coal measures as source rock and reservoir,and with adjacent tight layers as reservoirs or cap or transport layers.Under the action of source-reservoir coupling,coal-rock gas is accumulated in coal-rock reservoirs with good preservation conditions,tight oil/gas is accumulated in tight layers,conventional oil/gas is accumulated in traps far away from sources,and coalbed methane is accumulated in coal-rock reservoirs damaged by later geological processes.The proposed whole petroleum system of coal measures represents a novel type of whole petroleum system.
基金funded by the National Natural Science Foundation of China (No.52225402)Inner Mongolia Research Institute,China University of Mining and Technology-Beijing (IMRI23003)。
文摘In the gas-coal integrated mining field,the conventional design method of pipeline coal pillars leads to a large amount of coal pillars being unrecovered and overlooks the pipeline's safety requirements.Considering the coal pillar recovery rate and pipeline's safety requirements,two new shaped coal pillar design approaches for subsurface pipelines were developed.Firstly,the deformation limitations for measuring pipeline safety are categorized into two:no deformation is permitted,and deformation is acceptable within elastic limits.Subsequently,integrating the key stratum theory(KST)and cave angle,a fishbone-shaped coal pillar design approach that does not permit pipeline deformation is established.Meanwhile,combined with the ground subsidence and the pipeline's elastic deformation limit,a grille-shaped coal pillar design approach that accepts deformation pipelines within elastic limits is established.Those two new approaches clarify parameters including mined width,coal pillar width and mined length.Finally,the case study shows that the designed mined width,coal pillar width and mined length of the fishbone-shaped coal pillar are 90,80,and 130 m,while those of the grille-shaped are 320,370,and640 m.Compared with the conventional method,the fishbone-shaped and grille-shaped coal pillar design approaches recovered coal pillar resources of 2.65×10~6and 5.81×10~6t on the premise of meeting the pipeline safety requirements,and the recovery rates increased by 20.5%and 45.0%,with expenditures representing only 56.46%and 20.02%of the respective benefits.These new approaches provide managers with diverse options for protecting pipeline safety while promoting coal pillar recovery,which is conducive to the harmonic mining of gas-coal resources.
基金Supported by the China National Science and Technology Major Project(2025ZD1405700)CNPC Science and Technology Project(2023YQX20117).
文摘Based on the coalbed methane(CBM)/coal-rock gas(CRG)geological,geophysical,and experimental testing data from the Daji block in the Ordos Basin,the coal-forming and hydrocarbon generation&accumulation characteristics across different zones were dissected,and the key factors controlling the differential CBM/CRG enrichment were identified.The No.8 coal seam of the Carboniferous Benxi Formation in the Daji block is 8-10 m thick,typically overlain by limestone.The primary hydrocarbon generation phase occurred during the Early Cretaceous.Based on the differences in tectonic evolution and CRG occurrence,and with the maximum vitrinite reflectance of 2.0%and burial depth of 1800 m as boundaries,the study area is divided into deeply buried and deeply preserved,deeply buried and shallowly preserved,and shallowly buried and shallowly preserved zones.The deeply buried and deeply preserved zone contains gas content of 22-35 m^(3)/t,adsorbed gas saturation of 95%-100%,and formation water with total dissolved solid(TDS)higher than 50000 mg/L.This zone features structural stability and strong sealing capacity,with high gas production rates.The deeply buried and shallowly preserved zone contains gas content of 16-20 m^(3)/t,adsorbed gas saturation of 80%-95%,and formation water with TDS of 5000-50000 mg/L.This zone exhibits localized structural modification and hydrodynamic sealing,with moderate gas production rate.The shallowly buried and shallowly preserved zone contains gas content of 8-16 m^(3)/t,adsorbed gas saturation of 50%-70%,and formation water with TDS lower than 5000 mg/L.This zone experienced intense uplift,resulting in poor sealing and secondary alteration of the primary gas reservoir,with partial adsorbed gas loss,and low gas production rate.A depositional unification and structural divergence model is proposed,that is,although coal seams across the basin experienced broadly similar depositional and tectonic histories,differences in tectonic intensity have led to spatial heterogeneity in the maximum burial depth(i.e.,thermal maturity of coal)and current burial depth and occurrence of CRG(i.e.,gas content and occurrence state).The research results provide valuable guidance for advancing the theoretical understanding of CBM/CRG enrichment and for improving exploration and development practices.
文摘As an important pillar of China's industrialization process,the coal industry has not only made contributions to economic growth,but also left a large number of coal mine sites bearing historical memories.These sites are not only the witness of the industrial civilization,but also the potential resources for urban renewal and industrial transformation.
基金supported by the National Natural Science Foundation of China(Nos.52274242 and 51904293)the National Key R&D Program of China(No.2022YFC3004701)+2 种基金the Fundamental Research Funds for the Central Universities(No.2025QN1030)the Youth Science and Technology Talent Support Project of Jiangsu Province(No.JSTJ-2024-063)the Special Fund for Science and Technology of Jiangsu Province(No.BM2022013)。
文摘Deep mining is imperative,and the consequent coal and gas outburst disasters triggered during coal uncovering are becoming increasingly severe.Therefore,this study investigated the mechanical mechanisms of outburst instability from three dimensions:experiment,numerical simulation,and field application.Based on physical simulation tests with different outburst pore diameter,it was found that the gas pressure relief rate,gas emission volume,and outburst dynamic phenomena increase with outburst pore diameter.The migration patterns of the gas-solid two-phase flow evolved over time approximately into suspension flow,plug flow,dune flow,and stratified flow.The dominant influence of gas-driven tensile failure was amplified by uncovering coal area.The employment of the“fluid-solid-damage”coupling model revealed that coal damage,gas emission volume,deflection angle of outburst hole,roof displacement,maximum horizontal tensile stress,the horizontal tensile stress zone,the peak seepage force,and the damage zone all increased with uncovering coal areas.At the gas pressure of 0.74 MPa,when the uncovering coal areas were 3.189,4.754 and 6.225 m,the total gas emission volumes were 4.72×10^(-4),16.83×10^(-4),and 17.67 m^(2)/s,deflection angles of outburst hole were 150.79°,152.89°and 158.66°,the maximum roof displacements were 0.044,0.046,and 0.325 m,and the peak seepage force were 0.85,1.27,and 1.46 MPa/m,respectively.The regions of coal failure calculated by tensile failure criterion largely coincided with those calculated by the mixed failure criterion,far greater than those calculated by the shear failure criterion.As the increase of uncovering coal area,tensile weights of 80.72%,89.78%,and 93.01%,respectively.Comparisons with field outburst cases showed that both gas emission volume and outburst hole deflection angle reflected the tensile failure of coal.The mechanical instability process of outbursts under the influence of uncovering coal area and gas pressure was analyzed,developing the progressive cyclical method of coal uncovering,which provided a novel approach for the achievement of safe coal mining.
基金the Fundamental Research Funds for the Central Universities(2023YQTD02)National Key R&D Program of China(2023YFC2907501)。
文摘To address issues such as inefficient top-coal drawing,challenges in simultaneously mining and drawing,and the need for intelligent control in extra-thick coal seams,this study examines the principles of top-coal drawing and explores automation and intelligent equipment solutions within the framework of the group coal drawing method.Numerical simulations were performed to investigate the impact of the Number of Drawing Openings(NDO)and rounds on top-coal recovery,coal draw-ing efficiency,and Top Coal Loss(TCL)mechanism.Subsequently,considering the recovery and coal drawing efficiency and by introducing the instantaneous gangue content and cumulative gangue content in simulations,the top-coal recovery,gangue content,and coal loss distribution when considering excessive coal drawing were analyzed.This established a foun-dation for determining the optimal NDO and shutdown timing.Finally,the key technical principle and automated control of a shock vibration and hyperspectral fusion recognition device were detailed,and an intelligent coal drawing control method based on this technology was developed.This technology enabled the precise control of the instantaneous gangue content(35%)during coal drawing.The top-coal recovery at the Tashan Mine 8222 working face increased by 14.78%,and the gangue content was controlled at~9%,consistent with the numerical simulation results.Thus,the reliability of the numerical simulation results was confirmed to a certain extent.Meanwhile,the single-group drawing method significantly enhanced the production capacity of the 8222 working face,achieving an annual output of 15 million tons.
基金funded by the National Natural Science Foundation of China(Grant No.51934008,51674264 to Jiachen Wang,Grant No.51974320 to Shengli Yang)Fundamental Research Funds for the Central Universities(Grant No.06500182 to Zhengyang Song)Funds from State Key Laboratory of Coal Resources in Western China(SKLCRKF20-07 to Zhengyang Song).
文摘This review details the state of the art in research on top coal drawing mechanisms in Longwall top coal caving(LTCC)by examining the relevant literature over the last two decades.It startswith an introduction of the brief history and basic procedures of LTCC.The framework of research on the drawing mechanism,basic concepts,and some theoretical models of LTCC are detailed in sect.research framework of top coal drawingmechanism.The authors note that theTop coal drawbody(TCD),Top coal boundary(TCB)and Top coal recovery ratio(TCRR)are key factors in the drawingmechanism.TheBody-boundary-ratio(BBR)research system has been the classic framework for research over the last 20 years.The modified Bergmark-Roos model,which considers the effects of the supporting rear canopy,flowing velocity of top coal,and its shape factor,is optimal for characterizing the TCD.A 3Dmodel to describe the TCB that considers the thicknesses of the coal seam and roof strata is reviewed.In sect.physical testing and numerical simulation,the physical tests and numerical simulations in the literature are classified for ease of bibliographical review,and classic conclusions regarding the drawing mechanism of top coal are presented and discussedwith elaborate illustrations and descriptions.The deflection of the TCDis noted,and is caused by the shape of the rear canopy.The inclined coal seam always induces a largerTCD,and a deflection in theTCDhas also been observed in it.The effects of the drawing sequence and drawing interval on the TCRR are reviewed,where a long drawing interval is found to lead to significant loss of top coal.Its flowing behavior and velocity distribution are also presented.Sect.practical applications of drawingmechanisms forLTCCmines 4 summarizes over 10 cases where the TCRRof LTCCmines improved due to the guidance of the drawing mechanism.The final section provides a summary of the work here and some open questions.Prospective investigations are highlighted to give researchers guidance on promising issues in future research on LTCC.
基金supported by the National Natural Science Foundation of China(No.5217-4205)Shaanxi Provincial Outstanding Youth Science Fund Project(No.2023-JC-JQ-40)+4 种基金National Key Research and Development Project(No.2023YFC3009004)Key Project of Shaanxi Provincial Department of Education(No.22JY040)Xinjiang Uygur Autonomous Region Key Research and Development Task Special Project(No.2022B01034-3)Key Laboratory of Green Coal Mining in Xinjiang,Ministry of Education(No.KLXGY-KA2404)Shaanxi Provincial Key Research and Development Task General Project(No.2024GX–YBXM-490)。
文摘In this study,to better decide the effect of coal seam dip angle upon the dynamic change of the crossfusion in gas transport and storage areas during the progress of working face in the high gas thick coal seam,a two-dimensional physical simulation experiment regarded as the theoretical research was conducted to properly explore the variation law of overburden fracture.The results demonstrated that the boundary of the gas transport zone was located in the region of fracture separation.The boundary of the gas storage area was located in the abrupt penetration zone.Also,according to the information theory,the state of the gas transport and storage areas was determined by the changing trend of the fracture rate and fracture entropy.The mathematical representation model of the dip effect in gas transport and storage areas was established.The criteria upon which the regional location of the gas transport area and gas storage area can be based were put forward.The cross-fusion evolution process of the dip effect in gas transport and storage areas was revealed as well.The research results could provide guidance for realising directional and accurate gas extraction.
基金financially supported by the Geological Survey Project of China Geological Survey National Potential Evaluation of Coal Resources project(121211121043)the National Natural Science Foundation of China(41572141,41772156).
文摘The occurrence of coal-bearing strata in a variety of coal-bearing basins of China is characterized by late tectonic deformation and remarkable spatial and geochronologic differences.The main controlling factors,which determine the tectonic framework of coalfields,include the geodynamic environment,tectonic evolution,deep structures,tectonic stress,and lithologic combination of the coal measures.The Chinese continent has experienced multi-stage tectonic movements since the Late Paleozoic.The spatial and temporal heterogeneity of its continental tectonic evolution,the complexity of its basement properties,and its stratigraphic configurations control the tectonic framework of its coalfields’present complex and orderly patterns.The concept of coal occurrence structural units is proposed in this paper and is defined as the structural zoning of coal occurrence.China’s coalfields are divided into five coal occurrence structural areas,and the structural characteristics of the coalfields in five main coal occurrence areas throughout the country are summarized.Based on the analysis of the relationship between the structure characteristics and occurrence of coal in these coalfields,the coal-controlling structures are divided into six groups:extensional structural styles,compressional structural styles,shearing and rotational structural styles,inverted structural styles,sliding structural styles,and syn-depositional structural styles.In addition,the distribution of coal-controlling structural styles is briefly summarized in this paper.
基金financially supported by the National Key R&D Program(Nos.2023YFC3009000 and 2023YFC3006804)the National Natural Science Foundation of China(Nos.52130409,52121003,51874314,and 52274190).
文摘The hydraulic fractures induced in soft coal composite reservoirs have complex extension and energy evolution characteristics.In this study,the mechanism whereby gas outbursts can be eliminated by hydraulic fracturing was revealed.The combined fracturing process of a coal seam and its roof under different in situ stress and fracture spacing conditions was analysed through true triaxial physical tests and numerical simulations.The results showed that the pre-fracturing of the roof had a pressure relief effect on the coal seam,and the secondary pressure relief of the coal seam could be completed at a lower fracture initiation pressure.To ensure the continued presence of the stress shadow effect in actual projects,the fracture spacing should be maintained within the critical range influencing the fracture extension.If the vertical stress is high,a call on increasing the fracture spacing can be taken;otherwise,it must be reduced.In the early phase of fracturing,energy is mostly concentrated at the tip and surface of the fracture;however,the proportion of surface energy for subsequent fracturing is gradually reduced,and the energy is mostly used to open the formation and work on the surrounding matrix.Hydraulic fracturing creates new fractures to interconnect originally heterogeneously distributed gas zones,enabling the entire coal seam to first establish interconnected pressure equilibration,then undergo gradientcontrolled depressurization.Hydraulic fracturing can homogenize the stress field and gas pressure field in the original coal seam via communication pressure equalization and reduction decompression,reduce the elastic and extension energies,increase the minimum failure energy required for instability;and realize the elimination of gas outbursts.Our findings provide some theoretical support for the efficient development of coalbed methane and the prevention and control of dynamic gas disasters in coal mines.
文摘It is important to understand the effects of demineralization on the reactivity of coal pyrolysis for demineralization coal in OCCSS systems.The molecular dynamics of the pyrolysis of ZD-R and ZD-D was investigated using the ReaxFF MD method.It is indicated that the pyrolysis reactivity of ZD-D is enhanced.Acid demineralization treatment helps to enhance the cross-linking reaction of light tar C5-14 molecules in the main pyrolysis stage,generating light tar fragments with higher molecular mass.In the polycondensation pyrolysis stage,the acid demineralization treatment promotes the polycondensation reaction at high temperatures.The generation of H2 in ZD-R pyrolysis is primarily attributed to the N-H bond breaking in pyrrole at low temperatures.At high temperatures,it is predominantly associated with the hydrogen abstraction reaction between carboxyl functional groups and the dehydrogenation reaction of hydrogen bond breaking in the aliphatic hydrocarbon structures.H2O is primarily attributed to the reaction of the hydroxyl group on the carboxyl group.CO_(2) is always related to the carboxyl group.CO is mainly related to the reduction reaction of carbonyl group,carboxyl group,and CO_(2).During the initial pyrolysis stage of ZD-D after acid demineralization treatment,the hydrogen abstraction reaction of the carboxyl functional group and the generation of CO molecules by the methoxy group are enhanced.The generation of H2 by the aliphatic structure is enhanced in the main pyrolysis stage.The ring-opening reaction of the phenoxy group to generate CO in the polycondensation pyrolysis stage is also facilitated.
基金support from the National Natural Science Foundation of China(22408004)the Scientific Research Foundation for the Introduction of Talent,Anhui University of Science and Technology(2023yjrc90)+1 种基金the Fundamental Research Funds of the AUST(2024JBQN0015)the Open Research Fund Program of Anhui Provincial Institute of Modern Coal Processing Technology,Anhui University of Science and Technology(MTY202302).
文摘China has abundant resources of high-alumina coal(HAC).However,its application as a raw gasification material is limited owing to high ash-fusion characteristics.For overcoming the limitation,this study employed Xinjiang coal(XJ),having a low ash fusion temperature,to improve the ash fusibility and viscosity of high-alumina Jungar coal(JG).The evolution of Al-containing phases and structures during mixed ash melting were investigated based on XRD,XPS,27Al NMR,high-temperature stage microscopy(HTSM),and thermodynamic simulations.An increase in the XJ mass ratio resulted in the transformation of gehlenite to anorthite and mullite,producing more amorphous materials at high temperature.These phenomena were manifested at a microscopic imaging as an increase in the number of reaction/melting sites and their area expansion rate,as well as a decrease in ash area shrinkage and melting temperature.Moreover,the introduction of XJ altered the alumina-oxygen network,reducing the binding to the silicaoxygen network and converting some[AlO_(6)]^(9-)to[AlO_(4)]^(5-)as the relative concentration of O_(2)-and O-increases.Consequently,the decrease in the stability of the aluminate structure improves the AFT and viscosity.Based on these results,a mechanism to improve the ash fusion characteristics of HAC based on coal blending is proposed.
基金supported by Young Scholar Program(Category A Continuation Funding)of National Natural Science Foundation of China(No.52525401)General Program of National Natural Science Foundation of China(No.52174125)+4 种基金Outstanding Youth Cultivation Project in Shanxi Province(No.202103021222008)Major Program of National Natural Science Foundation of China(No.52334005)New Cornerstone Science Foundation through the XPLORER PRIZEShanxi-Zheda Institute of Advanced Materials and Chemical Engineering(No.2022SX-TD010)Shanxi Science and Technology Major Project(No.20201102004).
文摘Coal pillars are critical supporting structures between underground coal gasification gasifiers.Its bearing capacity and structural stability are severely threatened by high-temperature environments.To elucidate the high-temperature deterioration mechanism of coal pillars at multiple scales,coal strength features as a function of temperature were investigated via uniaxial compression and acoustic emission equipment.The pyrolysis reaction process and microstructure evolution were characterized via X-ray diffractometer(XRD),scanning electron microscope(SEM),thermogravimetric(TG),Fourier transform infrared spectroscopy(FTIR),and computed tomography(CT)tests.Experimental results reveal a critical temperature threshold of 500℃for severe degradation of the coal bearing capacity.Specifically,both the strength and elastic modulus exhibit accelerated degradation above this temperature,with maximum reductions of 45.53%and 61.34%,respectively.Above 500℃,coal essentially undergoes a pyrolysis reaction under N_(2)and CO_(2)atmospheres.High temperatures decrease the quantity of O_(2)-based functional groups,growing aromaticity and the degree of graphitization.These changes induce dislocation and slip inside the coal crystal nucleus and then lead to deformation of the coal molecular structural units and strain energy generation.This process results in a great increase in porosity.Consequently,the stress deformation of coal increases,transforming the type of failure from brittle to ductile failure.These findings are expected to provide scientific support for UCG rock strata control.
基金supported by the Fundamental Research Funds for the Central Universities(No.2024-10941)China University of Mining and Technology 2024 Graduate Innovation Program Projects(No.2024WLKXJ011)+1 种基金Jiangsu Graduate Student Research and Innovation Program(No.KYCX24_2846)the National Natural Science Foundation of China(Nos.52227901 and 51934007).
文摘Physical analog modeling is an effective approach for studying the hazards of coal bursts in coal similarity criteria for physical and mechanical parameters of the actual and similar materials are crucial to yield realistic results.The derivation of similarity criteria is predominantly based on dimensional analysis,while a systematic methodology has yet to be developed.This paper attempts to fill this gap by combining the equation transformation method with similarity theory to conduct an in-depth study on the similarity criteria of physical parameters of impact coal with various internal block sizes.On this basis,the influence of internal block size of impact coal on similarity criteria was studied.Block size can provide a selection basis for similar materials,and the influence of block size on model physical parameters and similarity criteria under different geometric similarity ratios was explored.The variation laws between geometric similarity ratio,block size,and physical properties were clarified,and the similarity criteria of impact coal under the influence of block size were adjusted.New insights into material selection for physical analog modeling were proposed.The established similarity criteria for impact coal under the influence of different block sizes can provide a theoretical basis for determining various parameters in the physical analog modeling of coal bursts,when building a physical model of impact coal,material selection and size selection can be based on similarity criteria to more accurately reproduce coal explosion disasters in the laboratory.
基金supported by National Natural Science Foundation of China(52104048,42272198)。
文摘Gas channeling in fractures during CO_(2) injection into the deep coal seam seriously reduces the CO_(2) storage efficiency after the development of coalbed methane.The generation and migration of coal fines causes blockages in the fractures in the stage of drainage and gas production,reducing the gas channeling effect of injected CO_(2) caused by the heterogeneity of the coal seam.To explore the impact of coal fines within coal seam fractures on the efficacy of CO_(2) storage,experiments on the production stage and CO_(2) injection for storage were conducted on coal combinations containing propped fractures,fractures,and matrix.The CO_(2) storage characteristics of coal at the constraint of coal fines,as well as the influence of multiple rounds of intermittent CO_(2) injection and different injection parameters on the CO_(2) storage effect,were analyzed.The research results show that blockage by coal fines increases the resistance to fluid flow in the fractures by 71.2%.The CO_(2) storage capacity and storage potential of coal with coal fines are 6.5 cm^(3)/g and 8.8%higher than those of coal without coal fines,while the CO_(2) storage capacity of fractured coal under the influence of coal fines has the largest increase of 9.4 cm^(3)/g.The CO_(2) storage of coal containing coal fines is significantly higher(6.6%)than that of the coal without coal fines.The CO_(2) storage effect of the coal with coal fines is improved with the increase in injection rate,whereas the CO_(2) storage effect of the coal without coal fines decreases significantly(by 7.8%).Multiple rounds of intermittent injection increases the CO_(2) storage volume of coal by 20.4%(with coal fines)and 17.1%(without coal fines).The presence of coal fines in fractures also slows down the downward trend of CO_(2) storage fraction after multiple rounds of CO_(2) injection.The blockage in fractures significantly increases the CO_(2) injection time and difficulty,but can increase the CO_(2) storage fraction by 4.7%-17.1%,and the storage volume by 1.9%-14%,increasing the feasibility of CO_(2) storage in fractured coal seams that have previously been exploited for methane production.The multiple rounds of intermittent CO_(2) injection and shut-in periods has shown potential for greater CO_(2) storage and injection efficiency.
文摘On 30 September 2024,the UK shuttered its last remaining coal-fired power plant[1].The closure marks a historic milestone,the end of 142 years of coal fueled prosperity.The country opened the world’s first plant to supply electric streetlamps in 1882,spark-ing a global energy revolution that has led to today’s nearly univer-sally electrified world.
基金National Natural Science Foundation of China(Project No.:U1905216).
文摘The issue of top contact in paste backfill materials is a common technical challenge in coal mine filling processes,and overcoming this problem has become a significant research direction in current studies and engineering practices.This paper utilizes coal gangue as aggregate and hydrogen peroxide as a foaming agent to prepare foamed paste backfill materials.Three close-packing theories were employed to investigate the effects of different coal gangue particle gradations on the mechanical properties,expansion ratio,water absorption,and dry density of foamed paste backfill materials under the same foaming agent content.The hydration mechanism and pore structure evolution were analyzed using XRD,SEM,and OSM techniques.The results indicate that when the hydrogen peroxide addition is 5%,the foamed paste backfill material regulated by MAA gradation theory exhibits the best comprehensive performance,achieving a 28-day compressive strength of 0.89 MPa,an expansion ratio of 155.5%,and a dry density of 1.24 g/cm^(3).The regulation of coal gangue aggregate particle gradation not only improves the foaming efficiency but also allows the formation of CH to fill the material pores,enhancing the overall structural support capacity and forming a closer microstructure.This research provides new insights into controlling the properties of foamed paste backfill materials.
基金supported by the National Natural Science Foundation of China(No.52074296)。
文摘In extremely close-distance coal seam(ECDCS)mining,section coal pillars remain after upper coal seam(UCS)extraction.Thus,for layout and support design of lower coal seam(LCS)mining roadways,it is critical to account for UCS goaf deterioration and residual coal pillar(RCP)-induced stress disturbance.Taking the 6.4 m layer spacing of ECDCS mining in Nanyangpo Coal Mine as a case study,this research aimed to determine the optimal layout and surrounding rock control method for the 24202-ventilation roadway in the RCP area.First,the challenges of roadway layout and support under RCP were clarified:three layout methods face distinct RCPinduced stress disturbances and goaf-related roof damage.A finite element model was established;the second invariant of deviatoric stress(J_(2))and horizontal stress index were introduced to analyze plastic zone and stress evolution after UCS mining.Results show that J_(2)distributes symmetrically,with its peak diffusing downward and attenuating in a“/”-shaped pattern.Six schemes were simulated to compare plastic zone distributions at different positions,revealing that the optimal layout consists of a roadway alignment with the RCP center.Based on roadway layout and roof conditions,a cooperative control scheme was proposed:deep,strong anchorage with long cables across the RCP,and shallow stable support with short bolts in the ECDCS.This scheme secures roof cables anchored to the UCS RCP roof to achieve cross-seam anchorage.On-site borehole peeping and loose circle tests confirm smooth surrounding rock hole walls and limited failure range.Specifically,surrounding rock deformation and roof separation were controlled within 200 mm and 80 mm,respectively,with stable bolt/cable support resistance.These results offer an innovative solution for roadway layout design and support strategies under RCP in ECDCS,with significant engineering application value.
基金supported by the National Natural Science Foundation of China(52274085).
文摘Coal bursts pose significant safety and operational challenges in deep mining environments,necessitating effective mitigation strategies to address high-stress concentrations and dynamic failure risks.This study evaluated the efficacy of hydraulic fracturing as a preconditioning tool at a longwall face of the Mengcun coal mine with strong coal bursts,Shaanxi Province.The program involved the systematic creation of a fracture network through high-pressure fluid injection,monitored via microseismic arrays,stress measurements,and hydrological sensors.Results demonstrated that hydraulic fracturing effectively redistributed in-situ stresses,reducing high-stress concentrations by up to 30%,lowering the frequency of high-energy microseismic events,and enhancing the stability of fractured zones.However,the presence of unfractured blind spots and interactions with pre-existing faults highlighted the need for optimized well placement and adaptive fracturing designs.These findings underscore the potential of hydraulic fracturing as a critical preconditioning tool in high-stress mining operations,which could provide a framework for improving safety and efficiency in similar geological and operational settings.
