Geological characteristics and exploration breakthroughs of coal rock gas in Carboniferous Benxi Formation,Ordos Basin,NW China

To explore the geological characteristics and exploration potential of the Carboniferous Benxi Formation coal rock gas in the Ordos Basin,this paper presents a systematic research on the coal rock distribution,coal rock reservoirs,coal rock quality,and coal rock gas features,resources and enrichment.Coal rock gas is a high-quality resource distinct from coalbed methane,and it has unique features in terms of burial depth,gas source,reservoir,gas content,and carbon isotopic composition.The Benxi Formation coal rocks cover an area of 16×104km^(2),with thicknesses ranging from 2 m to 25 m,primarily consisting of bright and semi-bright coals with primitive structures and low volatile and ash contents,indicating a good coal quality.The medium-to-high rank coal rocks have the total organic carbon(TOC)content ranging from 33.49%to 86.11%,averaging75.16%.They have a high degree of thermal evolution(Roof 1.2%-2.8%),and a high gas-generating capacity.They also have high stable carbon isotopic values(δ13C1of-37.6‰to-16‰;δ13C2of-21.7‰to-14.3‰).Deep coal rocks develop matrix pores such as gas bubble pores,organic pores,and inorganic mineral pores,which,together with cleats and fractures,form good reservoir spaces.The coal rock reservoirs exhibit the porosity of 0.54%-10.67%(averaging 5.42%)and the permeability of(0.001-14.600)×10^(-3)μm^(2)(averaging 2.32×10^(-3)μm^(2)).Vertically,there are five types of coal rock gas accumulation and dissipation combinations,among which the coal rock-mudstone gas accumulation combination and the coal rock-limestone gas accumulation combination are the most important,with good sealing conditions and high peak values of total hydrocarbon in gas logging.A model of coal rock gas accumulation has been constructed,which includes widespread distribution of medium-to-high rank coal rocks continually generating gas,matrix pores and cleats/fractures in coal rocks acting as large-scale reservoir spaces,tight cap rocks providing sealing,source-reservoir integration,and five types of efficient enrichment patterns(lateral pinchout complex,lenses,low-amplitude structures,nose-like structures,and lithologically self-sealing).According to the geological characteristics of coal rock gas,the Benxi Formation is divided into 8 plays,and the estimated coal rock gas resources with a buried depth of more than 2000 m are more than 12.33×10^(12)m^(3).The above understandings guide the deployment of risk exploration.Two wells drilled accordingly obtained an industrial gas flow,driving the further deployment of exploratory and appraisal wells.Substantial breakthroughs have been achieved,with the possible reserves over a trillion cubic meters and the proved reserves over a hundred billion cubic meters,which is of great significance for the reserves increase and efficient development of natural gas in China.

Disasters of gas-coal spontaneous combustion in goaf of steeply inclined extra-thick coal seams

In light of the escalating global energy imperatives,mining of challenging-to-access resources,such as steeply inclined extra-thick coal seams(SIEC),has emerged as one of the future trends within the domain of energy advancement.However,there is a risk of gas and coal spontaneous combustion coupling disasters(GCC)within the goaf of SIEC due to the complex goaf structure engendered by the unique mining methodologies of SIEC.To ensure that SIEC is mined safely and efficiently,this study conducts research on the GCC within the goaf of SIEC using field observation,theoretical analysis,and numerical modeling.The results demonstrate that the dip angle,the structural dimensions in terms of width-to-length ratio,and compressive strength of the overlying rock are the key factors contributing to the goaf instability of SIEC.The gangue was asymmetrically filled,primarily accumulating within the central and lower portions of the goaf,and the filling height increased proportionally with the advancing caving height,the expansion coefficient,and the thickness of the surrounding rock formation.The GCC occurs in the goaf of SIEC,with an air-return side range of 41 m and an air-intake side range of 14 m,at the intersection area of the“<”-shaped oxygen concentration distribution(coal spontaneous combustion)and the“>”-shaped gas concentration distribution(gas explosion).The optimal nitrogen flow rate is 1000 m3/h with an injection port situated 25 m away from the working face for the highest nitrogen diffusion efficacy and lowest risk of gas explosion,coal spontaneous combustion,and GCC.It has significant engineering applications for ensuring the safe mining of SIEC threatened by the GCC.

Advancing respirable coal mine dust source apportionment:a preliminary laboratory exploration of optical microscopy as a novel monitoring tool

Exposure to respirable coal mine dust(RCMD)can cause chronic and debilitating lung diseases.Real-time monitoring capabilities are sought which can enable a better understanding of dust components and sources.In many underground mines,RCMD includes three primary components which can be loosely associated with three major dust sources:coal dust from the coal seam itself,silicates from the surrounding rock strata,and carbonates from the inert‘rock dust’products that are applied to mitigate explosion hazards.A monitor which can reliably partition RCMD between these three components could thus allow source apportionment.And tracking silicates,specifically,could be valuable since the most serious health risks are typically associated with this component-particularly if abundant in crystalline silica.Envisioning a monitoring concept based on field microscopy,and following up on prior research using polarized light,the aim of the current study was to build and test a model to classify respirable-sized particles as either coal,silicates,or carbonates.For model development,composite dust samples were generated in the laboratory by successively depositing dust from high-purity materials onto a sticky transparent substrate,and imaging after each deposition event such that the identity of each particle was known a priori.Model testing followed a similar approach,except that real geologic materials were used as the source for each dust component.Results showed that the model had an overall accuracy of 86.5%,indicating that a field-microscopy based moni-tor could support RCMD source apportionment and silicates tracking in some coal mines.

Three dimensional discrete element modelling of the conventional compression behavior of gas hydrate bearing coal

To analyze the relationship between macro and meso parameters of the gas hydrate bearing coal(GHBC)and to calibrate the meso-parameters,the numerical tests were conducted to simulate the laboratory triaxial compression tests by PFC3D,with the parallel bond model employed as the particle contact constitutive model.First,twenty simulation tests were conducted to quantify the relationship between the macro–meso parameters.Then,nine orthogonal simulation tests were performed using four meso-mechanical parameters in a three-level to evaluate the sensitivity of the meso-mechanical parameters.Furthermore,the calibration method of the meso-parameters were then proposed.Finally,the contact force chain,the contact force and the contact number were examined to investigate the saturation effect on the meso-mechanical behavior of GHBC.The results show that:(1)The elastic modulus linearly increases with the bonding stiffness ratio and the friction coefficient while exponentially increasing with the normal bonding strength and the bonding radius coefficient.The failure strength increases exponentially with the increase of the friction coefficient,the normal bonding strength and the bonding radius coefficient,and remains constant with the increase of bond stiffness ratio;(2)The friction coefficient and the bond radius coefficient are most sensitive to the elastic modulus and the failure strength;(3)The number of the force chains,the contact force,and the bond strength between particles will increase with the increase of the hydrate saturation,which leads to the larger failure strength.

Mechanism of micro-wetting of highly hydrophobic coal dust in underground mining and new wetting agent development

The internal mechanism of the high hydrophobicity of the coal samples from the Pingdingshan mining area was studied through industrial,element,and surface functional group analysis.Laboratory testing and molecular dynamics simulations were employed to study the impact of three types of surfactants on the surface adsorption properties and wettability of highly hydrophobic bituminous coal.The results show that the surface of highly hydrophobic bituminous coal is compact,rich in inorganic minerals,and poorly wettable and that coal molecules are dominated by hydrophobic functional groups of aromatic rings and aliphatic structures.The wetting performance of surfactants as the intermediate carrier to connect coal and water molecules is largely determined by the interaction force between surfactants and coal(Fs-c)and the interaction force between surfactants and water(Fs-w),which effectively improve the wettability of modified coal dust via modifying its surface electrical properties and surface energy.A new type of wetting agent with a dust removal rate of 89%has been developed through discovery of a compound wetting agent solution with optimal wetting and settling performance.This paper provides theoretical and technical support for removing highly hydrophobic bituminous coal dust in underground mining.

Response characteristics of gas pressure under simultaneous static and dynamic load:Implication for coal and gas outburst mechanism

Coal and gas outbursts are dynamic disasters in which a large mass of gas and coal suddenly emerges in a mining space within a split second.The interaction between the gas pressure and stress environment is one of the key factors that induce coal and gas outbursts.In this study,first,the coupling relationship between the gas pressure in the coal body ahead of the working face and the dynamic load was investigated using experimental observations,numerical simulations,and mine-site investigations.It was observed that the impact rate of the dynamic load on the gas-bearing coal can significantly change the gas pressure.The faster the impact rate,the speedier the increase in gas pressure.Moreover,the gas pressure rise was faster closer to the impact interface.Subsequently,based on engineering background,we proposed three models of stress and gas pressure distribution in the coal body ahead of the working face:static load,stress disturbance,and dynamic load conditions.Finally,the gas pressure distribution and outburst mechanism were investigated.The high concentration of gas pressure appearing at the coal body ahead of the working face was caused by the dynamic load.The gas pressure first increased gradually to a peak value and then decreased with increasing distance from the working face.The increase in gas pressure plays a major role in outburst initiation by resulting in the ability to more easily reach the critical points needed for outburst initiation.Moreover,the stronger the dynamic load,the greater the outburst initiation risk.The results of this study provide practical guidance for the early warning and prevention of coal and gas outbursts.

Experimental investigations on effects of gas pressure on mechanical behaviors and failure characteristic of coals

The mechanical behavior of coal is the key factor affecting underground coal mining and coalbed methane extraction.In this study,triaxial compression and seepage tests were carried out on coal at different gas pressures.The mechanical properties and failure process of coal were studied,as well as the acoustic emission(AE)and strain energy.The influence of gas pressure on the mechanical parameters of this coal was analyzed.Based on the conventional energy calculation formula,the pore pressure was introduced through the effective stress formula,and each energy component of coal containing gas was refined innovatively.The contribution of gas pressure to the total energy input and dissipation during loading was quantitatively described.Finally,the influence of gas pressure on coal strength was theo-retically analyzed from the perspectives of MohreCoulomb criterion and fracture mechanics.The results show that the total absorbed energy comprises the absorbed energy in the axial pressure direction(positive)and in the confining pressure direction(negative),as well as that induced by the pore pressure(initially negative and then positive).The absorbed energy in the axial pressure direction accounts for the main proportion of the total energy absorbed by coal.The quiet period of AE in the initial stage shortens,and AE activity increases during the pre-peak stage under high gas pressure.The fractal characteristics of AE in three stages are studied using the correlation dimension.The AE process has different forms of self-similarity in various deformation stages.

Multi-scale pore fractal characteristics of differently ranked coal and its impact on gas adsorption

Well-developed pores and cracks in coal reservoirs are the main venues for gas storage and migration.To investigate the multi-scale pore fractal characteristics,six coal samples of different rankings were studied using high-pressure mercury injection(HPMI),low-pressure nitrogen adsorption(LPGA-N2),and scanning electron microscopy(SEM)test methods.Based on the Frankel,Halsey and Hill(FHH)fractal theory,the Menger sponge model,Pores and Cracks Analysis System(PCAS),pore volume complexity(D_(v)),coal surface irregularity(Ds)and pore distribution heterogeneity(D_(p))were studied and evaluated,respectively.The effect of three fractal dimensions on the gas adsorption ability was also analyzed with high-pressure isothermal gas adsorption experiments.Results show that pore structures within these coal samples have obvious fractal characteristics.A noticeable segmentation effect appears in the Dv1and Dv2fitting process,with the boundary size ranging from 36.00 to 182.95 nm,which helps differentiate diffusion pores and seepage fractures.The D values show an asymmetric U-shaped trend as the coal metamorphism increases,demonstrating that coalification greatly affects the pore fractal dimensions.The three fractal dimensions can characterize the difference in coal microstructure and reflect their influence on gas adsorption ability.Langmuir volume(V_(L))has an evident and positive correlation with Dsvalues,whereas Langmuir pressure(P_(L))is mainly affected by the combined action of Dvand Dp.This study will provide valuable knowledge for the appraisal of coal seam gas reservoirs of differently ranked coals.

Experimental and theoretical study on the dynamic effective stress of loaded gassy coal during gas release

In the process of mining coalbed methane(CBM),an unsteady state often arises due to the rapid extraction,release and pressure relief of CBM.In this case,the effective stress of coal changes dynamically,affecting the stability of the gassy coal seam.In this paper,gas release tests of gassy coal under conventional triaxial compression were performed,and the dynamic effective stress(DES)during gas release was obtained indirectly based on a constitutive equation and deformation of coal.The results show that the maximum increases in DES caused by the release of free gas and adsorbed gas under the stress of 1.1 MPa were 0.811 and 5.418 MPa,respectively,which seriously affected the stress state of the coal.During the gas release,the free gas pressure and the adsorbed gas volume were the parameters that directly affected the DES and showed a positive linear relationship with the DES with an intercept of zero.The DES of the coal sample increased exponentially with time,which was determined by the contents of free and adsorbed gas.Based on the experimental results and theoretical analysis,an effective stress model was obtained for loaded gassy coal during gas release.The results of verification indicated accuracy greater than 99%.

A systematic review of occupational exposure to respirable coal mine dust(RCMD)in the U.S.mining industry

Cumulative inhalation of respirable coal mine dust(RCMD)can lead to severe lung diseases,including coal worker's pneu-moconiosis(CWP),silicosis,mixed dust pneumoconiosis,dust-related diffuse fibrosis(DDF),and progressive massive fibrosis(PMF).Statistics from the number of reported cases showed a significant decrease in the progression of respiratory diseases in the 1990s.However,an unexpected increase in the number of CWP cases was reported in the late 1990s.To date,there has been no comprehensive systematic review to assess all contributing factors to the resurgence of CWP cases.This study aims to investigate the effects of various mining parameters on the prevalence of CWP in coal mines.A systematic review using the preferred reporting items for systematic reviews and meta-analysis(PRISMA)method was conducted to investigate the health effects of RCMD exposure and identify the factors that may contribute to the recent resurgence of CWP cases.The systematic review yielded a total of 401 papers,which were added to the database.The total number of 148 and 208 papers were excluded from the database in the process of screening and eligibility,respectively.Then,18 papers were considered for data selection and full-text assessment.The review revealed that factors including geographic location,mine size,mining operation type,coal-seam thickness,coal rank,changes in mining practices,technology advancement,and engi-neering dust control practices are contributing to the recent resurgence of CWP among coal workers.However,the evidence for root causes is limited owing to the methodological constraints of the studies;therefore,further detailed studies are needed.

Mechanism of gas pressure action during the initial failure of coal containing gas and its application for an outburst inoculation

Faced with the continuous occurrence of coal and gas outburst(hereinafter referred to as“outburst”)disasters,as a main controlling factor in the evolution process of an outburst,for gas pressure,it is still unclear about the phased characteristics of the coupling process with in situ stress,which induce coal damage and instability.Therefore,in the work based on the mining stress paths induced by typical outburst accidents,the gradual and sudden change of three-dimensional stress is taken as the background for the mechanical reconstruction of the disaster process.Then the true triaxial physical experiments are conducted on the damage and instability of coal containing gas under multiple stress paths.Finally,the response characterization between coal damage and gas pressure has been clarified,revealing the mechanism of action of gas pressure during the initial failure of coals.And the main controlling mechanism during the outburst process is elucidated in the coupling process of in situ stress with gas pressure.The results show that during the process of stress loading and unloading,the original gas pressure enters the processes of strengthening and weakening the action ability successively.And the strengthening effect continues to the period of large-scale destruction of coals.The mechanical process of gas pressure during the initial failure of coals can be divided into three stages:the enhancement of strengthening action ability,the decrease of strengthening action ability,and the weakening action ability.The entire process is implemented by changing the dominant action of in situ stress into the dominant action of gas pressure.The failure strength of coals is not only affected by its original mechanical strength,but also by the stress loading and unloading paths,showing a particularly significant effect.Three stages can be divided during outburst inoculation process.That is,firstly,the coals suffer from initial damage through the dominant action of in situ stress with synergy of gas pressure;secondly,the coals with spallation of structural division are generated through the dominant action of gas pressure with synergy of in situ stress,accompanied by further fragmentation;and finally,the fractured coals suffer from fragmentation and pulverization with the gas pressure action.Accordingly,the final broken coals are ejected out with the gas action,initiating an outburst.The research results can provide a new perspective for deepening the understanding of coal and gas outburst mechanism,laying a theoretical foundation for the innovation of outburst prevention and control technologies.

Elimination mechanism of coal and gas outburst based on geo‑dynamic system with stress–damage–seepage interactions

Coal and gas outburst is a complex dynamic disaster during coal underground mining.Revealing the disaster mechanism is of great signifcance for accurate prediction and prevention of coal and gas outburst.The geo-dynamic system of coal and gas outburst is proposed.The framework of geo-dynamic system is composed of gassy coal mass,geological dynamic environment and mining disturbance.Equations of stress–damage–seepage interaction for gassy coal mass is constructed to resolve the outburst elimination process by gas extraction with boreholes through layer in foor roadway.The results show the occurrence of outburst is divided into the evolution process of gestation,formation,development and termination of geo-dynamic system.The scale range of outburst occurrence is determined,which provides a spatial basis for the prevention and control of outburst.The formation criterion and instability criterion of coal and gas outburst are established.The formation criterion F1 is defned as the scale of the geo-dynamic system,and the instability criterion F2 is defned as the scale of the outburst geo-body.According to the geo-dynamic system,the elimination mechanism of coal and gas outburst—‘unloading+depressurization’is established,and the gas extraction by boreholes through layer in foor roadway for outburst elimination is given.For the research case,when the gas extraction is 120 days,the gas pressure of the coal seam is reduced to below 0.4 MPa,and the outburst danger is eliminated efectively.

Assessment of gas and dust explosion in coal mines by means of fuzzy fault tree analysis

During the past decade, coal dust and gas explosions have been the most two serious types of disasters in China, threatening the lives of miners and causing significant losses in terms of national property. In this paper, an evaluation model of coal dust and gas explosions was constructed based on a fuzzy fault tree by taking the Xingli Coal Mine as a research site to identify the risk factors of coal dust and gas explosions.Furthermore, the hazards associated with such explosions were evaluated for this particular coal mine.After completing an on-site investigation, the fuzzy probabilities of basic events were obtained through expert scoring, and these expert opinions were then aggregated as trapezoidal fuzzy numbers to calculate the degrees of importance of all basic events. Finally, these degrees of importance were sorted. According to the resulting order, the basic events with higher probabilities were determined to identify key hazards in the daily safety management of this particular coal mine. Moreover, effective measures for preventing gas and coal dust explosions were derived. The fuzzy fault tree analysis method is of high significance in the analysis of accidental coal mine explosions and provides theoretical guidance for improving the efficiency of coal mine safety management in a scientific and feasible manner.

Online coal dust suppression system for opencast coal mines

Coal is the major source of power in India and world over.Coal mining is an essential industry which has a major role in the economic development of the country.Most major mining activities contribute directly or indirectly to air pollution.Coal dust is a major air pollutant which affects the personal working in the mines and also people residing in villages near the mines.Air pollution due to coal particulates can affect human health and cause damages to the environment.Hence effective pollution control mechanisms are needed to keep the pollution levels within permissible levels.The easiest and most common method employed for dust suppression worldwide is sprinkling of water.In majority of mines,water sprinklers are operated manually and can lead to wastage of water due to over sprinkling.It can also prove to be ineffective in dust suppression if sprinkling is not done properly.The paper proposes a system which can be deployed to automate the dust suppressions sprinklers.The system will monitor the concentration of PM_(10) and PM_(2.5) in the air and initiate sprinkling operation when the particulate matter content exceeds preconfigured limits.

In-situ gas contents of a multi-section coal seam in Sydney basin for coal and gas outburst management

The gas content is crucial for evaluating coal and gas outburst potential in underground coal mining. This study focuses on investigating the in-situ coal seam gas content and gas sorption capacity in a representative coal seam with multiple sections (A1, A2, and A3) in the Sydney basin, where the CO_(2) composition exceeds 90%. The fast direct desorption method and associated devices were described in detail and employed to measure the in-situ gas components (Q_(1), Q_(2), and Q_(3)) of the coal seam. The results show that in-situ total gas content (Q_(T)) ranges from 9.48 m^(3)/t for the A2 section to 14.80 m^(3)/t for the A3 section, surpassing the Level 2 outburst threshold limit value, thereby necessitating gas drainage measures. Among the gas components, Q_(2) demonstrates the highest contribution to Q_(T), ranging between 55% and 70%. Furthermore, high-pressure isothermal gas sorption experiments were conducted on coal samples from each seam section to explore their gas sorption capacity. The Langmuir model accurately characterizes CO_(2) sorption behavior, with ft coefcients (R^(2)) greater than 0.99. Strong positive correlations are observed between in-situ gas content and Langmuir volume, as well as between residual gas content (Q_(3)) and sorption hysteresis. Notably, the A3 seam section is proved to have a higher outburst propensity due to its higher Q_(1) and Q_(2) gas contents, lower sorption hysteresis, and reduced coal toughness f value. The insights derived from the study can contribute to the development of efective gas management strategies and enhance the safety and efciency of coal mining operations.

Revaluating coal permeability-gas pressure relation under various gas pressure differential conditions

Identifying changes in coal permeability with gas pressure and accurately codifying mean efective stresses in laboratory samples are crucial in predicting gas-fow behavior in coal reservoirs. Traditionally, coal permeability to gas is assessed using the steady-state method, where the equivalent gas pressure in the coal is indexed to the average of upstream and downstream pressures of the coal, while ignoring the nonlinear gas pressure gradient along the gas fow path. For the fow of a compressible gas, the traditional method consistently underestimates the length/volume-averaged pressure and overestimates mean efective stress. The higher the pressure diferential within the sample, the greater the error between the true mean pressure for a compressible fuid and that assumed as the average between upstream and downstream pressures under typical reservoir conditions. A correction coefcient for the compressible fuid pressure asymptotes to approximately 1.3%, representing that the error in mean pressure and efective stress can be on the order of approximately 30%, particularly for highly pressure-sensitive permeabilities and compressibilities, further amplifying errors in evaluated reservoir properties. We utilized this volume-averaged pressure and efective stress to correct permeability and compressibility data reported in the literature. Both the corrected initial permeability and the corrected pore compressibility were found to be smaller than the uncorrected values, due to the underestimation of the true mean fuid pressure, resulting in an overestimation of reservoir permeability if not corrected. The correction coefcient for the initial permeability ranges from 0.6 to 0.1 (reservoir values are only approximately 40% to 90% of laboratory values), while the correction coefcient for pore compressibility remains at approximately 0.75 (reservoir values are only approximately 25% of laboratory value). Errors between the uncorrected and corrected parameters are quantifed under various factors, such as confning pressure, gas sorption, and temperature. By analyzing the evolutions of the initial permeability and pore compressibility, the coupling mechanisms of mechanical compression, adsorption swelling, and thermal expansion on the pore structure of the coal can be interpreted. These fndings can provide insights that are useful for assessing the sensitivity of coal permeability to gas pressure as truly representative of reservoir conditions.

Measuring stellar populations,dust attenuation and ionized gas at kpc scales in 10010 nearby galaxies using the integral field spectroscopy from MaNGA

As one of the three major experiments of the fourth-generation Sloan Digital Sky Survey(SDSS-IV),the Mapping Nearby Galaxies at Apatch Point Observatory(MaNGA)survey has obtained high-quality integral field spectroscopy(IFS)with a resolution of 1–2 kpc for104galaxies in the local universe during its six-year operation from July 2014 through August 2020.It is crucial to reliably measure the physical properties of the different components in each spectrum before one can use the data for any scientific study.In the past years we have made lots of efforts to develop a novel technique of full spectral fitting,which estimates a model-independent dust attenuation curve from each spectrum,thus allowing us to break the degeneracy between dust attenuation and stellar population properties when fitting the spectrum with stellar population synthesis models.We have applied our technique to the final data release of Ma NGA,and obtained measurements of stellar population properties and emission line parameters,as well as the kinematics and dust attenuation of both stellar and ionized gas components.In this paper we describe our technique and the content and format of our data products.The whole dataset is publicly available in Science Data Bank with the link https://doi.org/10.57760/sciencedb.j00113.00088.

Experiment study on the propagation laws of gas and coal dust explosion in coal mine

The experiment of gas and coal dust explosion propagation in a single lanewaywas carried out in a large experimental roadway that is nearly the same with actual environmentand geometry conditions.In the experiment,the time when the gas and coal dustexplosion flame reaches test points has a logarithmic function relation with the test pointdistances.The explosion flame propagation velocity rises rapidly in the foreside of the coaldust segment and comes down after that.The length of the flame area is about 2 timesthat of the original coal dust accumulation area.Shock wave pressure comes down to therock bottom in the coal dust segment,then reaches the maximum peak rapidly and comesdown.The theoretical basis of the research and assemble of across or explosion is suppliedby the experiment conclusion.Compared with gas explosion,the force and destructiondegree of gas and coal dust explosion is much larger.

Mechanism research of gas and coal dust explosion

Combined with the experimental results from the large tunnel of the ChongqingResearch Institute,the mechanism of gas and coal dust explosion was studied.Someconcepts about gas and coal dust explosion were introduced such as the form conditionand influential factors.Gas and coal dust explosion propagation was researched and thelifting process of coal dust was simulated.When an explosion occurred due to great mixtureof gas and air,the maximum explosion pressure appeared in the neighborhood of theexplosion source point.Before it propagated to the tunnel of the deposited coal dust,themaximum explosion pressure appeared to be in declining trend.Part of the energy waslost in the process of raising the deposited coal dust through a shock wave,so the maximumexplosion pressure was smallest on the foreside of the deposited coal dust sector.On the deposited coal dust sector,the explosion pressure rapidly increased and droppedoff after achieving the largest peak value.Because of coal dust participation in the explosion,the flame velocity rose rapidly on the deposited coal dust and achieved a basic stablevalue;coal dust was ignited to explode by initial laminar flame,and the laminar flametransformed into turbulent flame.The turbulence transformed the flame fold into a funnelshape and the shock wave interacted with the flame,so the combustion rate rose and thepressure wave was further enhanced.The regeneration mechanism between the flamecombustion rate and the aerodynamic flowing structure achieved the final critical state forforming the detonation.

Whole petroleum system in Jurassic coal measures of Taibei Sag in Tuha Basin,NW China

Based on the latest results of near-source exploration in the Middle and Lower Jurassic of the Tuha Basin,a new understanding of the source rocks,reservoir conditions,and source-reservoir-cap rock combinations of the Jurassic Shuixigou Group in the Taibei Sag is established using the concept of the whole petroleum system,and the coal-measure whole petroleum system is analyzed thoroughly.The results are obtained in three aspects.First,the coal-measure source rocks of the Badaowan Formation and Xishanyao Formation and the argillaceous source rocks of the Sangonghe Formation in the Shuixigou Group exhibit the characteristics of long-term hydrocarbon generation,multiple hydrocarbon generation peaks,and simultaneous oil and gas generation,providing sufficient oil and gas sources for the whole petroleum system in the Jurassic coal-bearing basin.Second,multi-phase shallow braided river delta–shallow lacustrine deposits contribute multiple types of reservoirs,e.g.sandstone,tight sandstone,shale and coal rock,in slope and depression areas,providing effective storage space for the petroleum reservoir formation in coal-measure strata.Third,three phases of hydrocarbon charging and structural evolution,as well as effective configuration of multiple types of reservoirs,result in the sequential accumulation of conventional-unconventional hydrocarbons.From high structural positions to depression,there are conventional structural and structural-lithological reservoirs far from the source,low-saturation structural-lithological reservoirs near the source,and tight sandstone gas,coal rock gas and shale oil accumulations within the source.Typically,the tight sandstone gas and coal rock gas are the key options for further exploration,and the shale oil and gas in the depression area is worth of more attention.The new understanding of the whole petroleum system in the coal measures could further enrich and improve the geological theory of the whole petroleum system,and provide new ideas for the overall exploration of oil and gas resources in the Tuha Basin.