Search

Coalbed methane, tight gas and shale gas(three gases) occurred in coal bearing strata are rich in resources and achieving a co-production from one well bore will significantly improve the resource recovery rate and economic benefits. However, the flow state of gas and water under the co-production process are still unclear. In this paper, a two layered gas reservoirs model in fractured vertical well was firstly established using the equivalent seepage theoiy. The production equation was proposed and the factors influencing the production rate during the gas drainage and gas-water co-producing rate was also analyzed. The results show that;the multi-layer linear seepage equation is established by referring to the parallel principle,and the reasonable production pressure difference can also be acquired;during the water drainage period, the smaller the physical compressibility is, the higher the water production rate, and the higher the pressure difference is, the flow discharge radius and the initial permeability affect the water production rate,but show little influence on reasonable pressure difference; during the gas and water co-production period, the initial permeability and Langmuir stress constant have some influence on reasonable pressure difference, however, the coal compressibility, fracture diversion ability and elastic modulus have little effect on pressure difference determination. The results are of significance in clearing the flow process of gas and water, conducting production analysis, and establishing reasonable drainage system. [ABSTRACT FROM AUTHOR]

The co-production of coalbed methane, tight gas and shale gas( “Three gases” ) from one well bore is an effeclive method to improve the productivity of single well and utilization rate of underground resources. However, the gas and water production process under geological conditions, especially the contribution rate from different layers,gas production pressure and gas saturation variation are not clear. In this paper, a numerical model of coalbed methane and light sand gas co-production was established for the first time. Combined with the geological parameters and gas-water output curve of the test well,the factors controlling the gas production were identified. The results show that that the applicability of the co-production model can be compared with single production models,which shows a good suitability; the model can achieve the purpose of production rate classification and the contribution of different layers can be classified; the pressure drop rate decreases, the later of the gas production peak come, however, the production rates in late stages show no much difference; the similar of the sandstone and coal pressure systems, the better of the co-production effect; improving the hydro fracturing results can improve the gas production rate in short term, but show little influence on the accumulated gas production; the effect of shrinkage and stress sensitivity of the coals can significantly improve the gas production effect, however, the physical properties of the coal seam under deep geological conditions need to be further explored. The related results would provide a guidance for the formulation and improvement of drainage systems of coal measure gases and promote “three gases” co-production from one wellbore a step further. [ABSTRACT FROM AUTHOR]

Classification evaluation of CBM wells provides a basis for the adjustment of coalbed methane reservoirs. However, there exist some disadvantages such as interfering with various factors,and subjectivity of choosing classification rule during classification evaluation. Besides, it is hard to assess the immediate effect of fracturing on CBM production, as methane recovery involves a process of drainage, depressurization and desorption. In this paper, an improved classification evaluation method of CBM wells was presented, based on data mining and seepage theory. CBM production distribution curve was plot using data through normalization, with normalized well number on horizontal axis and normalized production on vertical axis,whose derivative value was recognized as the criterion of classifying CBM wells. Method of production analysis was then used to evaluate the fracturing effect on different kinds of CBM wells. Classification was carried out in a gas field of Hancheng as well as assessing fracturing effect. Results show that the hydraulic fracture length of low yield well HS16 was short,skin factor increased during recovery, fracture conductivity was damaged and flow channels was blocked. Possible production after repeated fracturing was 300 m3/d. High yield well HS14 had a long fracture length and uninfluenced fracture conductivity. Production after fracturing was predicted to be 1 300 m3/d. [ABSTRACT FROM AUTHOR]

Depth of coal seams in Linxing middle area of the east margin of Ordos is more than 1 000 m,which has reached the research field of deep CBM.Based on the actual production data, this paper discusses the gas bearing capacity of deep coal seam, and refines the development geological model of deep coal seam in the area. The study shows that critical depth of the deep coal seam divided by the turning of gas content is about 2 000 m in the work area. Adsorption sensitivity of deep middle coal rank reservoirs is less sensitive to temperature than the pressure, so that critical depth of medium rank coal seams is relatively deeper than that of high rank coal seams. Deep coalbed gas is still mainly adsorbed gas, and the existing isothermal adsorption testing method is easy to cause the misunderstanding of the proportion of free gas in deep coalbed methane. Due to the influence of temperature, the deep coal seam is relatively high in temporary storage ratio. Due to the influence of stress, the reservoir properties are poor. The gas wells generally have the characteristics of “quick gas seepage, difficult drainage pressure reduction and slow gas production increase”. The potential of deep coalbed methane is huge. The experience of gas well shows that rational and optimized development unit is the key to the single-well breakthrough in deep coal seams. The enriched development geological model associated with Type A “source-reservoir” is a development model that is mainly considered in the breakthrough of deep seams. [ABSTRACT FROM AUTHOR]

The coal seams in eastern Yunnan and western Guizhou have the characteristics of vertical multi-layer lamination and the structural weak surfaces of the cleavage cracks are relatively developed. In previous research, the simulations of fractures propagation in multiple thin layers are mostly aimed at sandstone reservoirs, and the research on the influence of natural fractures on hydraulic fracturing is mostly aimed at shale and fractured sandstone.Therefore, there is a lack of systematic theoretical research on the propagation of hydraulic fractures in thin coal reservoirs with natural fractures, high Poisson’s ratio and low Young modulus. In this paper, a pseudo three dimensional fractures propagation model was established, considering the dynamic distribution of interlayer flow and the characteristics of cleat fracture development. Taking the coal reservoirs in eastern Yunnan and western Guizhou as an example, the propagation of fractures in each layer was simulated and analyzed. The research shows that the different distributions of natural fractures leads to the morphology of fractures in each layer having great differences；the width of fractures captured by natural fractures will decrease, and the risk of sand plugging will increase；the differences of liquid injection volume of each layer will be relatively small when the coal seam has a low Young’s modulus； for wells with determined perforated parameters, the increase of the viscosity of fracturing fluid and the increase of the injection rate can reduce the difference of flow between layers, and then promote the full expansion of each seam length； the fractures height will be decreased by reducing the viscosity and injection rate of fracturing fluid. [ABSTRACT FROM AUTHOR]

In order to make full use of coal mineral resources rationally, and provide the government departments with a decision basis for coal-gas resources comingled exploration and exploitation in Ordos area of Inner Mongolia, based on the geological data collected from coal exploration and coalbed methane exploitation in Ordos area, this study analyzed the geological background, structural characteristics and gas resources potential of the Ordos area by means of geology survey, sample analysis and comprehensive research. Thus this paper expounds that coal seam gas resources in Ordos area have great potential. It has a unique combination mode of multilayer systems, composite, sources closely linked, mutual stacking, and good storage cover, and has the resource condition for the combined exploration and exploitation. Also, the study has studied the advantages and disadvantages in Ordos area of Inner Mongolia, and put forward the suggestions and measures of the combined exploration and exploitation of coal seam gas. [ABSTRACT FROM AUTHOR]

In order to reveal the deep coal reservoir adsorption characteristics of coal and the quantitative characterization on the amount of adsorbed gas of coalbed methane, this paper studied the coal samples of carboniferous-permian in eastern Ordos Basin and analyzed the methane isothermal adsorption experiments of high temperatures and pressures of coal samples. An interpretation of the adsorption characteristics was made under high temperatures and pressures from the geological factors including coal rank, temperature and pressure. The curves of coal adsorption characteristic and the prediction model of amount of adsorbed gas with different coal ranks were established based on the adsorption potential theory. Meanwhile, a case study on the amount of adsorbed gas of the No. 8+9 coal seam in Linxing area was analyzed based on this model. The results show that the adsorption characteristics of deep coal reservoir are comprehensively influenced by temperature,pressure and coal rank. When the coal rank is between 0.77% and 2.18%, which is from gas coal to poor coal, the coal rank and pressure show a positive effect on adsorption ability, but temperature has a negative effect. In addition, the negative effect is more significant with the pressure increases. Different coal ranks have different curves of coal adsorption characteristic. The higher of coal rank, the slower of rate at which the adsorption potential decreases as the adsorption space increases. The calculation of the amount of absolute adsorbed is between 19.6 cm3/g and 31.1 cm3/g, and the gas saturation is between 37.8% and 78.8% in the study area [ABSTRACT FROM AUTHOR]

With the constant development of production technology, the co-exploration of coal measure gas becomes possible. Since the co-exploration of coal measure gas is based on the co-existence of coal measure gas, the study on the co-existence of coal measure gas has important guiding significance to the co-exploration. Based on the study of source rock, reservoir rock and cap rock of coal measure gas in Linxing block, eastern Ordos Basin, as well as the observation of rock core and field geology trip, this paper summarizes the co-existence patterns of coal measure gas, and discusses the origin mechanism of coal measure gas in terms of sedimentation and diagenesis. Results show that No. 8+9 coal seams in Benxi formation and Nos. 4+5 coal seams in Shanxi formation are the main source rocks. Dark muddy shales have a certain capacity of hydrocarbon generation. The type of sandstone is mainly lithic sandstone, whose average porosity is 6. 2% and average permeability is 0. 14×10-15 m2, meaning it belongs to tight sandstone. Tight sandstone, shale and coal seam are cap rock to each other, which leads to 14 combination modes between any two of tight sandstone gas, gas and coalbed methane. And the composition pattern of coal measure gas can be divided into four categories. Sedimentation determines the formation of CMG and the diagenesis affects its co-existence. [ABSTRACT FROM AUTHOR]

Linxing block，located in the eastern part of the Ordos basin, is one of the key areas of exploration and development of unconventional gases in coal series, in China. This paper discusses the paragenesis and enrichment law of coal measure gases and their control factors of Linxing block from the point of tectonic-thermal effect. Impacted by the intrusion of Zijinshan magmatic rock mass, the regional monocline tectonic pattern was superimposed into three secondary structural units, named as central uplift zone, annular fold zone and monocline structural belt, and the difference of deformation characteristics in secondary tectonic units determined the different paragenesis types and enrichment features of coal measure gases. The geothermal gradient and reservoir pressure gradient in coal series decreased in order from the central uplift belt, which leads to the lower gas content of coalbed methane and shale gas, but tight sandstone gas showed opposite trend. The distribution of groundwater salinity showed that the hydrodynamic condition of the annular fold belt was the weakest so that where was favorable for the adsorption gas preservation. According to the characteristics of main control factors of gas enrichment in different secondary structural units, the coal measure gases reservoir models have been proposed with “magmatic intrusive type→syncline and hydraulic sealing type→low-angled monocline and lithologic sealing type” which correspond to central uplift zone, annular fold zone and monocline structural belt. [ABSTRACT FROM AUTHOR]

Low-grade coal is difficult to obtain high efficiency by conventional flotation due to its poor surface hydrophobicity.In addition,the reactivity between low-grade coal and oxygen is high,so it is prone to spontaneous combustion.However,there is less oxygen in coal bed or internal dump,so the coal mainly suffers high temperature baking(similar to low temperature pyrolysis environment).Low temperature pyrolysis has gradually become one of the ways of efficient transformation and utilization of low-grade coal.Therefore,it is of great significance to explore the effect of low temperature pyrolysis on the hydrophobicity of low-grade coal and to reveal the change of the floatability of pyrolysis solid products.In this paper,non-caking coal was used as the object of study,and the weight loss characteristics of coal sample pyrolysis were depicted by thermo-gravimetric analyzer(TGA).Gas/liquid chromatography(GC/LC) was used to detect the composition of volatile products during pyrolysis.X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy(SEM) were used to characterize the functional groups and microstructure of coal samples before and after pyrolysis.The induction time and unit flotation tests were used to analyze the changes of hydrophobicity and floatability of coal samples before and after pyrolysis.The results show that the coal sample is deprived by low temperature pyrolysis,and a large number of volatile components(hydrogen,methane and other gaseous products,phenol-based liquid products) escapes,which leads directly to the content of hydrophilic oxygen-containing functional groups on the coal surface.The content of hydrophobic functional groups increased,the surface porosity and cracks increased significantly and the roughness increased.Compared with the raw coal,the pyrolysis half-coke induction time was shortened and the flotation yield was significantly increased.The low temperature pyrolysis enhances the hydrophobicity of the non-stick coal surface,and improves the flotation recovery rate,which promotes the technology development of “low temperature pyrolysis-semi-coke flotation and upgrading”. [ABSTRACT FROM AUTHOR]

In order to find out the spontaneous combustion characteristics and affecting mechanism of long term soaked long-flame coal,this paper analyzed the low temperature oxidation characteristics of long-flame raw coal and soaked and air-dried coal.The effect on the microcosmic structure,self-heating process,activation energy and so on was also analyzed.The results show that the coal soaked in water for a long time has a more developed surface pore structure,the average pore size,mesoporous volume and micro-pore volume increase at different degrees.Simultaneously,some of organic and inorganic substances on the coal surface will be dissolved in water,the concentration of free radical in coal increased and the group distribution has obvious change compared with the raw coal.After 90 and 180 days of water immersion,the amount and rate of gas production during the low temperature oxidation process are higher,the cross point temperature is reduced from 160.9 ℃ to 157 ℃ and 151.5 ℃,the activation energies decreased by 3.84 kJ/mol and 4.18 kJ/mol,respectively.And the soaked and air-dried coals have higher spontaneous combustion tendency.This study provides a scientific guidance for prevention and control of spontaneous combustion of the soaked and air-dried coal in shallow buried close distance coal seam group mining overlying coal goaf in western privinces. [ABSTRACT FROM AUTHOR]

The aim of this paper is to quantitatively evaluate the effect of mining-induced damage on the stability of joint rock slope.By means of site survey and fuzzy C-mean optimization algorithm,the random distribution parameters of the dip direction,dip angle,trace length and density of two dominant joint sets in footwall migmatite slope of Dagushan iron mine were obtained.Considering the relationships among Hoek-Brown parameters (m,s) and Geological Strength Index (GSI) and disturbance coefficient (D),the random distribution parameters of jointed rock mass strength were obtained by Monte Carlo method.After establishing the relationship between the damage and disturbance parameters of jointed rock mass,the Kawarnoto damage tensor was employed to carry out the numerical simulation of the mining-induced damage.Then the random distribution parameters (D) and rock mass strength with spatial-temporal distribution characteristics and anisotropy were obtained according to the Rosenblueth principle.The slope reliability index was calculated based on the strength parameters of rock mass with spatial-temporal distribution characteristics.The result shows that while the elevation of the stope bottom decreases from -87 m to -450 m,the reliability index of slip circle from the top of slope to -87 m level decreases 7.7% relatively.This is because that the increase of mining depth aggravates the damage in joined rock mass and weakens its strength.The potential slip surface gradually move to the slope surface,which has a greater correlation with the damage in rock masses near the slope. [ABSTRACT FROM AUTHOR]

Coal and rock masses in deep mining would bear dynamic disturbances which propagated deeper into the coal rock mass in the form of stress wave.These stress waves were mainly composed of high order P-waves with high frequency,fast phase velocity and many wave numbers.Because of the absorption and dispersion effect in the propagation of waves,the high order P-waves would change into low order P-waves with low frequency,slow phase velocity and less wave numbers.And the compressive and tensile stresses occur alternately,which could cause the strong vibration and serious damage of the coal and rock.Taking cylindrical coal and rock as an example,this paper obtained the frequency equation of P-waves,and established a dynamic calculation model for the displacement,strain,stress,vibration velocity and energy based on the propagation characteristics of P-waves and wave control equations.The simulation results showed as follows:under the action of low order P-waves,the vibration of radial and shear stress waves were relatively gentle,which could be considered as an effect of quasi-static loading.Shear failure of coal-rock mass would mainly occur and distribute near the surface.Under the action of low order P-waves,the vibration amplitudes of displacement,strain,stress,vibration velocity and energy decreased with the increase of radius dimensionless along the radial direction of the cylindrical coal rock,which followed the power function.The amplitudes of shear stress and strain were the largest,but the energy attenuation was the fastest.The authors noticed,most surprisingly,that the amplitude directions of the radial and axial stress waves were almost opposite,with the amplitude values basically same when the vibration kept stable.When there was no confining pressure,the cylindrical coal and rock mass eventually displayed crashing or splitting failure which was mainly caused by tensile stress.However,the conical failure easily occurred when there was confining pressure,which was tensile-shear failure.The maximum amplitude of displacement,strain,stress,vibration speed and energy were all located at the axis of action surface of the cylindrical coal and rock.Therefore,the initial damage position of coal and rock would be in the center of action surface. [ABSTRACT FROM AUTHOR]

The tunnels often cross joints and faults,which have great influence on tunnel stability during their use.In this paper,these joints and faults were approximated as the cracks through the tunnel.In order to study the influence of the cracks crossing the tunnel on tunnel stability under biaxial pressure,some model tests and numerical simulation were implemented.In the experiment study,Longchang sandstone was used to build tunnel models which were a square plate containing a small “tunnel” and an inclined fault,and in the simulation,Abaqus software was used.Using Abaqus software,the stresses at the points around the tunnel and the stress intensity factor of crack tips were calculated which agreed well with the experimental results.The results show that:① Different angle cracks would have different influence on the stability and strength of tunnel,and produced different stress concentration at the crack tips.When θ is around 40 degrees,the influence of crack on the overall stability and strength of tunnel is maximum,the stress concentration at crack tips is most obvious,KII value is maximum,its shear failure is more serious,and the peak of failure stress is only 41.77% of that of tunnels without cracks.② When θ is around 0 degrees,KII value is close to zero,under vertical pressure the cracks close,the stress concentration of crack tips are not obvious,the cracks are more steady,the failure stress of tunnel is maximum which is 91.23% of that of tunnels without cracks,and this position is the strongest for the tunnel stability.③ Under the influence of vertical stress and confining pressure,the tunnel failure is mainly the pressure-shear failure of the spandrels,side walls,crack tips,and skewbacks,and the tensile failure of arch bottom,vault. [ABSTRACT FROM AUTHOR]

In order to overcome the problem of long period and high cost for testing the uniaxial compressive strength of rock,a method for testing the uniaxial compressive strength of rock based on digital drilling is proposed.According to the characteristics of the rock drilling process,this paper deduces the relationship between rock unit cutting energy and the drilling parameters based on the energy analysis method.At the same time,based on the self-developed multi-function rock drilling test system,the authors carried out the digital drilling test of intact rock,such as sandstone and different strength mortar specimen.Based on the analysis of the test results,a quantitative relationship model (DP-UCS model) between the drilling parameters and the uniaxial compressive strength of the rock was established and verified.The results show that the deviation rate between the uniaxial compressive strength predicted by the DP-UCS model and the uniaxial compressive strength measured by the uniaxial compression test is less than 10%,the validity of the model is proved. [ABSTRACT FROM AUTHOR]

Based on the composition and properties of coal resources and the energy value as the benchmark,the paper presents the ideas of the near-zero ecological environmental impact of coal development and utilization,and discusses the basic theory of deep mining mechanics,the theory of ultra-low damage mining of coal,the theory of green and efficient development,the basic theory of prevention and treatment of major disasters,the new theory of coal and gas mining,the theory of coal and water mining,the new theory of high efficiency combustion of coal,the clean conversion theory of coal,the theory of deep removal of conventional pollutants,and the theory of capture and utilization of carbon dioxide,etc.From the two aspects of the intelligent exploitation of the near zero ecological damage and the clean and low carbon utilization of the near zero pollutant emission,the “13th Five-Year”,the next 15 years and the 30 years are formed.Replacing Technology (before 2020),expanding and changing technology (2020—2035 years),leading and exploring technology (2035—2050 years) have formed a revolutionary theory and technical system of the coal revolution,providing a guidance for a long period of scientific and technological innovation. [ABSTRACT FROM AUTHOR]

In order to solve the structure failure and column wreck problem of roadway hydraulic support in rock burst, a kind of component that can quickly abdicate and absorb impact energy is designed, which is used in gantry energy absorption and anti-impact hydraulic support. And then the component is used to protect hydraulic columns and the overall structure of support from damage. In this paper,the structural and energy-absorption performance of energy-absorption component is studied. Firstly, five performance requirements of energy absorption component were proposed according to the anti-impact function of gantry energy absorption hydraulic support, which are bearing capacity, reaction force changes, energy absorption, energy absorption and stability. Then,the structure design and mechanical principle of energy absorption component were discussed in detail, and the buckling energy absorption mechanism of component was analyzed by numerical simulation. Finally, the mechanical properties of 1 : I energy absorption component was studied by laboratory experiments. The experimental results show that the bearing capacity of energy absorption component is 2 428 kN,and the post-buckling reaction is relatively stable. When the compression is 50% ,the average energy is 357 kj. The absorption energy is transformed into the irreversible deformation energy of component. The buckling process is stable and close to the numerical simulation result. [ABSTRACT FROM AUTHOR]

According to the carrier flotation theory,this paper provides a method of using flotation cleaned coal as autogenous- carrier to improve the flotation efficiency of coal slime. This method tends to fix the problem that because the ash of flotation cleaned coal is often higher than the required ash and the yield of clean coal is low, the production operation is difficult for the coal slime containing fine particles and high ash clay. Moreover,the results show that the coal slime flotation effect can be significantly improved by this method. Experiment results illustrate that with the increase of the amount of autogenous-carrier, the clean coal yield, the flotation perfect index and the tail coal ash are increased, besides the ash of the flotation cleaned coal is reduced. This flotation process has been used to separate the slime from Wuhai and the feedback shows the yield of flotation refined coal increases by 7. 11%, ash content decreases by 1. 14% and the improvement index of flotation improves by 7. 25% . Furthermore, the results show the optimum dosage of autogenous-carrier is 10% of the floating slime and the stable flotation effect can be achieved after 3 -4 cycles by adding autogenous-carrier. The EDLVO theory has been studied and the results show that the hydrophobicity of the cleaned coal itself and the adsorption of the collector on the coal particle surface lead to the hydrophobic force which encourages the fine coal particles are adhered to the coarse particle carrier and the hydrophobic flocculation occurs between the fine particles. Finally,the flotation environment and flotation effect were improved. [ABSTRACT FROM AUTHOR]

This paper focused on the problem of the source localization of coal mine gas release. Due to the existence of wind leakage,it is difficult to find the location accurately by using the conventional algorithms. In this study,a multisource sensor fusion based algorithm for locating the coal mine gas release was proposed. Firstly, the gas distribution in the goaf of a fully mechanized working face was analyzed and the observation model ol mine goaf area and the diffusion model of gas release were established. Then,the gas release source parameters of goaf were estimated using the Mixed Kalman Particle Filter algorithm ( MKPF) , and the coordinate of the estimated parameters was obtained according to the iterative operation. Finally, the data of wireless sensor target source sensing nodes and cluster head nodes were fused to locate the accurate coordinate of the gas release source. The research concludes that the MKPF algorithm has obvious advantages in accuracy localization, which can effectively overcome the difficulty of gas release source localization impacted by wind leakage. It can provide support for gas warning and gas drainage in goaf. [ABSTRACT FROM AUTHOR]

There are widely distributed thick aeolian sand layer covering the surface of the auxiliary inclined shaft of the Jinjitan Coal Mine,Yulin,Shaanxi province. The floor of the auxiliary inclined shaft ruptured due to the repeat roller compaction of large tonnage vehicles on the floor during a short time, which resulted in water and sand inrush and seriously threatened the safety of the mine. Aiming at the problem of water and sand inrush of the Jinjitan Coal Mine, cement grouting treatment was implemented first and it played an important role in sealing water and sand inrush, but water inflow was not completely plugged. Then the remaining water inflow was successfully plugged by chemical grouting. Based on the engineering practice and model test, the reasons for the rupture of the floor, effect of the grouting treatment and reinforcement mechanism of different grout were analyzed in this paper. The results of field treatment and model test show that the cement grouting reinforced sand by tree-like propagated grout veins, the chemical grouting reinforced sand by splitting and infiltration, which is more advantageous to seal off the residual pathway of water inflow. Therefore the combining use of cement and chemical grouts has been proved a good efficiency. [ABSTRACT FROM AUTHOR]

Elastic reverse time migration (RTM) is an important technology in multi-component seismic exploration. In order to suppress noise in RTM and correct polarization of S-wave,the propagation directions of P-wave and S-wave have to be calculated accurately. The propagation direction of seismic wave is generally indicated by Poynting vector. The conventional first-order velocity-stress equations could only calculate a Poynting vector which indicates the propagation direction of the mixed wavefield rather than that of the P-or S-wavefield. Therefore, it is unable to accurately suppress noise or correct S-wave polarity by using the conventional Poynting vector. Theoretically, the first-order velocity- dilatation-rotation equations could calculate Poynting vectors of pure P-and S-wavefield,which indicate the propagation directions of P-and S-wave, respectively. Therefore, the problems in the conventional method could be avoided by using the Poynting vectors calculated by the first-order velocity-dilatation-rotation equations. This paper focuses on the elastic RTM which is based on the first order velocity-dilatation-rotation equations. Firstly, the authors derived a reverse- time propagation scheme in staggered-grid with 2-order time difference accuracy and 2 N-order space difference accuracy. The authors also derived the stability condition of the scheme. Secondly,the authors calculated the P-and Swave Poynting vectors to indicate the propagation directions of pure P-and S-wavefield,respectively. Then,the elastic RTM could be implemented by utilizing a cross-correlation imaging condition in the wavefield which is separated by propagation directions. The numerical tests show the elastic RTM based on the first-order velocity-dilatation-rotation equations can accurately correct S-wave polarization. In addition,the migrated sections obtained by this method could suppress noise better than the conventional method which is based on the first-order velocity-stress equations. [ABSTRACT FROM AUTHOR]

This paper describes a new method for determining the individual sources of goaf gas emissions in Shihe coal mine. Desorbed gases from coal seam No. 3 and its seven neighboring seams were respectively sampled and analyzed of iheir composition including CH4 ,C2H6, stable carbon isotopes in CO2 and hydrogen isotopes in CH4. Based on the analyzed results,a mathematical model was developed for calculating the sources of goaf gas emissions. The model was then applied in No. 5302 panel in Shihe coal mine to determine the emission sources of the goaf gas from each of the coal seams. The results show that CH4 concentration, stable carbon isotopes in CO2 and hydrogen isotopes in CH4 in creased with the depth of No. 3 seam. In terms of the characteristics of goaf gas emissions in No. 5302 panel, it can be divided into three stages with the panel advance. In the initial stage,the goaf gas emission was dominated with gas desorbed from the mining No. 3 seam, this dominance weakened as the panel advances and stabilized at around 20% - 25% of the total goaf gas emissions. In the second stage,gas from neighboring seams started to play an important role in the goaf gas,taking up 20%-25% of the total goaf gas emissions. In the third stage,the sources of the goaf gas emission became stable and gases desorbed from No. 9 and No. 15 seams made up 20% -25% and 30% -35% of the total goaf gas emissions respectively. This isotopes based method,in comparison with the tradition method for determining the sources of goaf gas emissions, can give quantitative description of dynamic change in the individual sources of goaf gas emissions with the advance of a mining panel, enabling a more targeted and effective control of goaf gas emissions. [ABSTRACT FROM AUTHOR]

In order to study the characteristics of anisotropic seepage of coal bearing methane, the raw coal samples were taken. Based on the tri-axial seepage experimental system the study of anisotropic seepage rule of coal hearing methane was carried out. The calculation method of the principal value and its azimuth of anisotropic permeability of coal bearing methane were determined. Permeability anisotropic ratio of coal bearing methane was defined. Permeability anisotropic dynamic variation rule and the phenomenon of the change of the dominant flow direction of coal bearing methane were analyzed emphatically. The results show that the flow of methane of coal has the very obvious characteristics of anisotropy, the calculation method of anisotropy permeability of coal bearing methane proposed in this paper is simple and effective. The coal bearing methane has strong stress-sensitivity, and the variation rule between permeability of methane of coal and effective stress is according with negative exponential function. The change of the permeability anisotropy of methane of coal with effective stress shows an obvious dynamic change law of development, the dominant flow direction of methane of coal exists the phenomenon of change. [ABSTRACT FROM AUTHOR]

Multiple discontinuities exist in the natural rock mass and these discontinuities are geometrically rough. In this paper, a rough discrete fractures network model ( RDFN) considering the complex and rough geometry distribution of discontinuities is introduced and tested under direct shear test using PFC2D. The corresponding shear behaviors, such as shear strength, shear modulus and failure pattern, were studied and compared with the traditional linear discrete fractures network (DFN) model. Numerical results show that fracture surface roughness can significantly affect the shear behavior of rock masses. The peak strength and shear modulus of the RDFN model are ralatively higher than those of the DFN model. The principal shear fractures in the DFN model mainly coincided along the linear joints. Parts of the intact rock elements were fractured. The failure pattern of RDFN model is much more complex and more intact rock elements were fractured after peak shear strength. The peak shear strength and modulus of all jointed rock models decrease with the increase of sample sizes. The value of shear modulus of the RDFN model is higher than that of the DFN model. The values of shear strength tend to be stabilized with the scale size reaching 4 . 0 m according to the scale effect analysis. [ABSTRACT FROM AUTHOR]

Because of the large mining thickness at one-time for extra thick seam using fully-mechanized top coal caving method and nearly shallow buried depth, the characteristics of surface movement and deformation particularity is obvious. Under this condition, its surface subsidence prediction has a certain degree of deviation with ihe actual situation. This paper analyzed the partic-ularity of surface movement and deformation for extra thick seam using fully-mechanized top coal caving method and nearly shallow buried depth of the test area. Considering thick-hard rock layer on surface subsidence control function,and based on layered elastic beam slab strata of subsidence control theory and random medium theory,the authors established a set of surface subsidence prediction model which is suitable for nearly shallow buried depth and extra thick seam using fully-mechanized top coal caving method. Practical application shows that degree of agreement for the prediction model algorithm with the experimental results is good,which is suitable for surface subsidence prediction application in extra thick seam mining using fully-mechanized top coal caving method. The prediction model algorithm preferably solved the problems such as rapid boundary convergence and unsymmetrical basin using probability integral method and improved the prediction accuracy of surface subsidence. [ABSTRACT FROM AUTHOR]

The reverse fault will slip with workface excavation in footwall. As the stresses loading on the combined sample were equal in the X and Y direction, the stress and strain along the fault,as well as acoustic emission signals,were monitored during the coal excavation. The analytical results show that stress decrease zone,stress increase zone and in situ stress zone occurred around the gob and their evolution will cause fault slip. Compared with normal fault, reverse fault has higher slipping risk under the same mining condition. As the workface locating in the footwall of reverse fault advances forward,the ratio of vertical force and horizontal force caused by mining increases from 1 to 6 ,which means the slipping risk of reverse fault rise. The strain along the fault face is not even,and the strain of coal seam is higher than that of rock strata. The energy of 84% of the acoustic events caused by coal mining are between 10-13 J and 10-10 J and their focus mainly concentrate in the roof strata and unlikely transpass the fault face which means the fault can cut-off the stress disturbance of mining. The conjunction of coal seam and fault face tends to cause large acoustic events which means this area has high slip risk. Compared with the in situ seismicity in Zhaolou Coal Mine,the spatial location of seismic focus and experimental acoustic focus have similar features to some extent, which could prove the feasibility of the experimental method adopted in this paper. [ABSTRACT FROM AUTHOR]

Aiming at the problem of applying charge induction method of measuring low dust concentration is not accurate,this paper proposes to reduce the middle parts of current measuring pipes' diameter,and form the contraction segment,throat segment,diffusion segment three parts,to improve the movement speed of dust particles by venturi effect,and then increase the inductive charge of electrostatic sensors.The experiments simulate the gas-solid two phase flow in the improved measurement pipeline by Fluent software,obtaining the velocity distribution of dust particles and the speed value in the throat segment.According to the mathematical model of loop static sensor,the inductance of different pipe diameter ratios is calculated.The results show that the inductive charge on the static sensor reaches the largest,when the improved pipe diameter ratio is 0.69.Through the optimization of measuring device,the accuracy of measurement can be increased by 3%,the measurement accuracy of low concentration dust is improved effectively. [ABSTRACT FROM AUTHOR]

A novel combustion system has been applied to a 600 MW Babcock & Wilcox (B & W) down-fired boiler to reduce NOx emissions without obvious increasing of the carbon content in fly ash.The modification mainly includes rearranging secondary air,and introducing separated over-fire air (SOFA).The aim of this work is to evaluate the overall performance of the novel combustion system with different SOFA ratios (e.g.,15%,20%,and 25%) and different SOFA locations in the upper furnace (e.g.,3.0,4.0,5.0,and 6.0 m above the arches) using numerical simulations.In order to calculate the carbon content of fly ash more accurately,this paper used CBK coke combustion mode.Results showed that not only the NOx emissions were greatly reduced from 823 mg/m3 to 738 mg/m3，but also the carbon content in the fly ash decreased slightly in 0.264% with increasing the SOFA ratio from 15% to 20%.When the SOFA ratio increased from 20% to 25%,NOx emissions only decreased 32 mg/m3,but the combustible content in the fly ash increased obviously in 0.41%.Considering the NOx emissions and combustible content in the fly ash,an SOFA ratio of 20% was advisable.With increasing the height of SOFA from 3.0 to 6.0 m above the arches,the carbon content in the fly ash somewhat increased while NOx emissions decreased.Taking economic efficiency and NOx emissions into account,the location (5.0 m above the arches) was the optimal SOFA location. [ABSTRACT FROM AUTHOR]

The pyrolysis technology for cascade utilization of low rank coal have been attracted much attention in recent years.Xinjiang is one of the important coal-chemical industrial base in China.But the fundamental research on pyrolysis of Xinjiang coal is relatively few.In this paper,the single stage (without iso-thermal stage,defined as process 1) and multi stage (with iso-thermal stage at 350 ℃ and defined as process 2,with iso-thermal stages at 350 ℃ and 450 ℃ and defined as process 3) pyrolysis characteristics of a typical Xinjiang coal (Hefeng coal) were first investigated by using a thermogravimetric analyzer(TGA) and a fixed bed reactor.The results showed that the weight loss of coal samples during the single stage and multi stage pyrolysis in TGA exhibited a little difference.The multi stage pyrolysis led to the increase of gas yield and decrease of tar yield,especially for process 3,in which the tar yield further decreased to 11.35%,about 15.42% decrement compared with that in process 2.The H2 yield was only 1.94 mL/g when temperature was lower than 450 ℃.Further increase temperature from 450 ℃ to 600 ℃,no tar was formed,while gas yield accounted for 60.87% of total gas amount,especially for H2 which accounted for 95.02% of total H2 yield.It indicates that gaseous products was mainly collected in this temperature range.FTIR analysis showed that only slight difference of the functional groups between the char obtained at 350 ℃ pyrolysis and raw coal was observed.While these functional groups nearly disappeared in char obtained at 450 ℃.The simulating distillation and NMR analysis results showed that holding stage in coal pyrolysis was favorable to upgrade the tar quality,which was embodied by the decrease of pitch content and the aromatic carbon ratio,especially for the two stage holding pyrolysis.Based on that,a theoretical basis for staged thermal conversion of low rank coal was supplied. [ABSTRACT FROM AUTHOR]

Hydrogeological condition is one of the most important factors controlling the migration,dispersion,distribution and accumulation of coalbed methane (CBM) in coal reservoir.In this paper,the water produced from CBM wells in Gujiao mining area was monitored in terms of concentrations,water quality and salinity.Then,combined with the local gas content and the distribution characteristics of groundwater,the geological controlling mechanisms on gas distribution characteristics in different units were discussed.Results show that the main ions of produced water were Na+,HCO3- and the type was NaHCO3.The total dissolved solids (TDS) of produced water were relatively lower,which ranged from 632 to 2 512 mg/L,belonging to freshwater-saline water.The research area were divided into runoff zone,weak runoff zone and stagnant zone,and the stagnant zone according to discounted water level and TDS.The stagnant zone had the highest gas content,while the gas content in the weak runoff zone was relatively lower.The enrichment of Gujiao mining area was controlled by structure and hydrogeological conditions.Now two hydraulic patterns were identified:The monocline-hydraulic sealing in the central of Malan was the richest area and the horst-hydraulic sealing in Dongqu was the richer area. [ABSTRACT FROM AUTHOR]

Seepage velocity and temperature reflect the changes in the structure and energy of coal and can be used as early warning signals of coal and gas outburst.In this paper,the briquette was taken as the research object,and the self-developed test system was used to determine the joint response of seepage velocity and temperature under triaxial loading.The loading rate effect on gas seepage velocity and temperature was studied,and the relationship between gas seepage velocity and temperature and coal failure was established.The results show that:① During loading process,gas seepage velocity decreases first and then increases,and it changes suddenly at the peak of stress.With loading rate increases,the Vmin decreases first and then increases,while (Vmax-Vmin) increases first and then decreases.② With stress increases,gas temperature increases linearly,and the (Tmax-Tmin)decreases.③ When the loading rate is low,the seepage velocity appears “quiet period” at 80% of coal rupture.When the loading rate is high,the seepage temperature fluctuates many times before rupture and there is a longer “quiet period”.Those can be used as effective early warning information to highlight the coal rupture. [ABSTRACT FROM AUTHOR]

Bedding structures are widespread and has a tremendous threat to stability of mine pillars.In this paper,the uniaxial compression tests (UCT) and CT scanning tests have been carried out on bedding rock and homogeneous massive rock.Through the analysis of acoustic emission (AE) characteristics,energy dissipation and transfer law in the process of the damage evolution of rock specimens,the damage model based on AE parameters and energy dissi-pation has been established.The results show:firstly,the mainly failure mode of rock specimens with bedding structure is inclined plane shear failure,with the obvious shear fracture zone.But homogeneous massive specimens are mainly featured by tensile failure and formed longitudinal fracture face,with brittle failure characteristics.And the weak structure of the bedding will weaken the bearing capacity of the pillar to a certain extent.Secondly,the failure of bedding rock occurs mainly in the plastic strain stage,it corresponds to AE violent period.Its axial loads are in the 60%σc-σc range and its failure time is within the range from the 63%tc to tc.The period for failure prediction of homogeneous massive rock should focus on before and after the yield point.The trend of dissipation of the strain in this interval is slowly decreasing (before the yield point c) → rising (after the yield point c) → sudden increase (failure point d).Thirdly,the damage model based on parameters of AE and energy dissipation is verified through real data computation and experiments,which shows that the average deviation rate of bedding rock is 8.2% and 9.5% and to homogeneous massive rock is 18.4% and 19.3%. [ABSTRACT FROM AUTHOR]

In order to investigate the coupling control of reducing coal pillar pressure concentration and realizing uniform surface subsidence to reduce surface cracks in shallow buried coal seams mining,the physical simulation and numerical calculation are employed.The interval strata breaking form,the concentrated stress distribution of coal pillars,the overburden and surface cracks and the ground surface subsidence in different coal pillar stagger distances are obtained.The relationship of the coal pillar stagger with the evolution of coal pillar stress concentration and of overburden fracture is discovered.According to the study,the determination of the reasonable upper and lower coal pillars stagger by interval layer breaking form can avoid the section coal pillar concentrated stress superposition and non-uniform strata subsidence in coal pillar supporting influence area,and realize the coupling control of stress and cracks in shallow coal seam group mining.In this paper,the control model of concentrated stress and ground crack of coal pillar group is established,and the coupling criterion to avoid the coal pillar concentrated stress and realize the uniform surface subsidence is put forward,so the mechanism of reducing the stress concentration of coal pillar and realizing the uniform subsidence of the ground surface is revealed. [ABSTRACT FROM AUTHOR]

Field investigations and theoretical studies show that the dynamic damage of the coal and rock system is characterized by static-dynamic coupling loads.During the preparation and development of rockburst the electromagnetic emission can represent energy accumulation while microseismic events represent the output of energy which indicates microseismicity has a duality of energy release and dissipation.So it is unscientific if the electromagnetic emission strength which stands for the energy accumulation and microseism energy that presents energy release are separately used as the criterion for rock burst forecast.Based on energy principles the precursory rules of rock burst are studied in this paper combining with the electromagnetic emission and microseismic monitoring method,the coupling evaluation system was established based on the monitoring results of a specific rockburst colliery.The results show the precursory rules that the elec-tromagnetic emission strength is much higher than normal and micro-seismic energy is continuously lower as well as the activity number appears an increase tendency.Rock burst will not occur if the micro-seismic activities are on the steady energy release estate even though the electromagnetic emission strength is higher. [ABSTRACT FROM AUTHOR]

There are too many creep models at present,but none has summarised these models' applicability,advantages and disadvantages yet.Also,the relation between coal rock creep and low gas pressure is unclear.Therefore,the creep test of coal rock under different gas pressures at triaxial stress was carried out to study the influence of gas on creep,and the applicability of various common creep models.The results show that the larger the gas pressure is,the greater the axial strain of coal and rock.The coal creep is positively correlated with the gas pressure.Then,the experimental data were used to test these common creep models.It was found that the empirical equations,such as the power function,exponential function and polynomial function,can only fit one of the decay or non-decaying creep.The Nishihara model cannot fit the non-decaying creep,and the Burgers model and its improved model has a few defects in fitting the decay and non-decaying creep curves.The Nishihara acceleration model has hysteresis,when it is used to fit the non-decaying creep of coal rock.And the Nishihara acceleration model is suitable for sandstone creep but not for coal rock creep.In this paper,the Nishihara acceleration model was improved.It is concluded that the improved Nishihara acceleration model can better describe the creep of coal rock.In addition,the theory of creep inflection point was presented.The creep curve at least has one creep inflection point,which is the necessary and sufficient condition for the non-decaying creep of rock.It not only enhances the theory of acceleration creep,but also has some guiding significance to prevent rock steady failure and other engineering practices. [ABSTRACT FROM AUTHOR]

Deep resource exploitation is imperative,but it is facing with more complicated mining environment and dangerous mining disturbances to induce the potential catastrophe process.Combined with the challenge of “four high and one disturbance” in deep coal mining and the technical advantages of backfilling mining in ground control,this paper summarizes five major technical problems faced by deep backfilling mining,thus the conception of green mining integrating mining,separating and backfilling in deep coal resources is put forward.The theoretical research and technical system of the conception have been basically formed which has been carried out in typical mines such as the 12th Coal Mine of Pingdingshan Group and Tangshan Coal Mine of Kailuan Group.In order to build integral theories and technology system of the green mining integrating mining,separating and backfilling in deep coal resource,backfilling and ground control theory in deep coal mine and five other basic theories need further researches and beyond that,seven key technologies such as the layout of mining-dressing-backfilling green mining system,automatic backfilling,mass flow material transportation and intelligent coal-waste separation need to be developed.These theories and techniques provide a reliable basis for realizing the safe,efficient and green mining of deep resources. [ABSTRACT FROM AUTHOR]

Dynamic disasters are the main factors relating to the safe and stable coal mine production.Therefore,more and more collieries need to carry out assessments for determining both the rockburst danger lever and prevention regions at the working face design stage.In this situation,it is urgent to develop new methods of rockburst risk early evaluation and timely warning characterized by much more scientific,accurate,quantitative and easily to operate for technical personnel.In order to address the problem that rockburst phenomenon cannot be expressed by the existing strength criterion as well as different stress cannot be assessed by scalar superposition,the authors put forward a new method of rockburst risk assessment using relative stress concentration factor superposition.The ration that divided by the maximum principal stress induced by a certain influencing factor of rockburst and the gravity stress in the area to be analyzed is defined as relative stress concentration factor component,and then the product of each component is named as relative stress concentration factor of the region.In this paper,the stresses relating to rockburst are classified into static and dynamic loads based on the strain rate character,and into decompression and supercharge based on the effects on stress state.The main factors causing dynamic loads and the relative stress concentration factor calculation method are analyzed in this study.The total relative stress concentration factor is used as the critical indicators in the coal mines where rockburst had been occurred while the ration of critical stress and weight stress as the threshold in the areas where rockburst never happened.Using the specific value of relative stress concentration factor and threshold,the authors established the rockburst risk lever system which has been proved to be more accurate,more conducive and beneficial to guide a safe production by field application. [ABSTRACT FROM AUTHOR]

In order to improve the crushing efficiency and rock breaking ability of coal and rock,a method of axial vibration and radial cutting of coal rock with wedge is proposed.Using the mechanical method of combination of compression,shear which are dominated at different stages,the paper analyzes the mechanical relationships of disc plate single tooth width in the extrusion,fracturing and fragmentation stages,as well as the disk with wedge to large lump coal rock collapse each process.Based on the superposition principle of compound effects,a mechanical model under various working conditions is built to reveal the mechanical mechanism of the broken coal rock on the edge of the tooth disc.The research shows that based on the mathematical description of the process of the formation of small pits,the generation of cracks and caving,through the process of caving of large chunks under the wedge,the mathematical model of radial and axial load is built with the parameters of the disc structure and the rock breaking parameters.The axial upward movement of the composite axis is favorable to the fracture of coal rock.The radial and axial load of disc cutter increases with the increase of cutting thickness.The radial and axial loads of the disc are 11% and 4% difference between the numerical simulated results.And the radial and axial loads of the disc are 3% and 18% when the composite action cutting is performed.The variation law of the parameters such as the thickness of the rock is consistent with the theoretical calculation and numerical simulation.The study provides a theoretical reference for the development of high efficiency and high crushing capacity. [ABSTRACT FROM AUTHOR]

Coalbed methane high efficiency production from broken soft and low permeable coal seams has been being a technical bottleneck of restricting coalbed methane industrialization development and coal mine gas control for many years.This paper has investigated the No.8 broken soft and low permeable coal seam in Lulling coal mine of Huaibei mining area in Anhui Province,China.Site investigation,sampling and testing,theoretical analysis,hydraulic fracture physical and numerical simulation have been performed.As a result,a new model of coalbed methane high efficiency production from broken soft and low permeable coal seam by roof strata-in horizontal well and staged hydraulic fracture has been presented,the hydraulic fracture extension and control mechanism under this model have been revealed,and the main technological processes of the model implementation have been given.The results show that the roof strata are relatively brittle and have high propagation pressures,while the broken soft coal seam is relatively plastic and has a low propagation pressure.When case perforation and hydraulic fracture are performed in horizontal well of the roof strata,the hydraulic fractures in roof strata,on the vertical,extend downward and penetrate the broken soft coal seam.At the same time,the hydraulic fractures also get rapid horizontal extension,and the traction engendered by this rapid horizontal extension rips the coal seam to form long hydraulic fractures in the coal seam.Numerical simulation results show that the hydraulic fracture length formed in the broken soft and low permeable coal seam when fracturing in roof strata is long as 6.7 times as that when fracturing directly in the coal seam.Those hydraulic fractures formed in the roof strata and the broken soft coal seam are filled with sand proppant in follow-up adding-sand fracturing,and come into being a coalbed methane migration pathway from the underlying coal seam to the roof strata-in horizontal well.It can be seen that broken soft coal seam can get a good fracturing stimulation effect in this new model.The results of this study are applied to the coalbed methane development demonstration project by roof strata-in horizontal well and staged hydraulic fracture in Luling coal mine of Huaibei mining area in Anhui province,China and have obtained a good gas production effect.The average daily gas production rate of the single coalbed methane horizontal well was respectively 10 358 m3,9 039 m3,7 921 m3 in three,six and twelve consecutive months.As of November,16,2017,this horizontal well already produced 5 million cubic meters of coalbed methane gas,and its daily gas production rate was still over 3 200 m3.This has created a new record of gas production of a single coalbed methane horizontal well from broken soft and low permeable coal seam in China. [ABSTRACT FROM AUTHOR]

To realize the integrated management of coal mine spatial information is an important foundation of intelligent mine construction.Based on the analysis of the status quo at home and abroad,the paper puts forward the concept of establishment of coal mine spatial data management platform,construction of distributed collaborative “one map”,expounds the key technological solutions of the realization of the coal mine “one map” software platform architecture,standard system,unified temporal spatial data management,spatial data service,distributed collaborative update released,and develops a Coal Mine Geographic Information System with independent intellectual property rights.Yangquan Coal Industry Group,Shenhua Coal Group,China Coal Energy Group and other units have practical applications,and the effect is very good. [ABSTRACT FROM AUTHOR]

Existing research that relevant to thermodynamic disaster is artificially divided into gas disaster,fire disaster and coal dust disaster.The drawback of the division is that it fails to systematically construct a theoretical system,which makes the systematical and synthetical prevention and control of this kind of disaster unavailable.In this paper,a large number of serious and extraordinary coal mine accidents happened in China and other countries are collected and analyzed,based on which the concept of thermodynamic disaster is proposed.The theoretical system of thermodynamic disasters is also constructed.Several hot issues about thermodynamic disasters are analyzed and discussed,which are the compound disaster involving coal mine gas and coal fire,the safety of low gas coal mine,the role of gas drainage played in the prevention of gas accidents,the relationship between accident and management,the efficiency of inert medium in preventing and extinguishing coal fires,the effect of mine explosion-proof facilities,self-escape after thermodynamic disaster.Seven misconceptions are pointed out. [ABSTRACT FROM AUTHOR]

Filling reclamation is an effective way to increase the amount of farmland.The existing reclamation technology adopts one-time filling measures,which leads to classic two-layers soil profile pattern with “soil layer+ filling material layer”.As covering soil is insufficient,the productivity of reclaimed farmland is usually low.This paper put forward a multi-layered soil profile pattern with inter-layers of filling materials.Taking filling reclamation of subsidence land with Yellow River Sediments as an example,this study analyzes the principles and methods of inter-layers reclamation.The results show that:Adding a soil layer as inter-layer in filling material layer could improve the moisture and nutrition situations of filling material,overcome the disadvantages of two-layer soil profile pattern with “soil layer+ filling material layer”,and increase the quality of reclaimed farmland.An alternate multilayered multi-filling method for soil reconstruction with reclaimed mining subsidence was proposed.The continuous construction technology of multilayered soil profile reconstruction is realized through alternate filling process,multiple filling and soil backfilling.Practices were carried out in Qiuji Mine of Shandong Province.Interlayer soil profile pattern has certain influence on wheat output.The wheat outputs of some profile patterns are higher than that of the control group. [ABSTRACT FROM AUTHOR]

Coalbed methane,tight sand gas and shale gas (three gases) are superimposed in coal measures,and whether achieving co-production successfully from on well bore determines the development efficiency and technology research direction of unconventional natural gases in coal measures.The paper discusses the co-production feasibility of “three gases”,based on the analysis of “three gases” occurrence characteristics and the status of coalbed methane and tight sand gas co-production test wells in Linxing area,east margin of Ordos Basin.The results show that the key for efficient co-production of “three gases” is to discharge the water from stratus by pumping equipment,and decrease the bottom hole pressure gradually.During the continuous production process,the gas and water production from one layers showed no influence to other layers.However,when the production stopped,the working water level may arise and flush into low-pressure strata due to differences in reduction degree of strata energies.Based on the field test,it can be concluded that the co-production of “three gases” is feasible,and different reservoirs show a form of river tributaries flow into the main stream or circuit parallel connection with gases being produced together when going into the well bores.The above is “parallel reservoirs combination with synergetic gas and water flow,downhole monitoring with wellhead controlment”.The further researches should be focused on studying appropriate workover process to prevent reservoir damage during well stops. [ABSTRACT FROM AUTHOR]

The clay content of shale gas reservoirs in China is high,and most shale reservoirs are located in water-deficient areas.The SC-CO2 fracturing is expected to be a new non-aqueous fracturing method because of its characteristics of low viscosity and low surface tension.In this paper,the comparison tests of SC-CO2 fracturing and hydraulic fracturing in shales and sandstones were carried out under triaxial conditions.The fracture morphology was investigated by CT scanning and the effect of temperature on fracturing was studied.The results show that the initiation pressure of SC-CO2 fracturing in shale is about 50.9% lower than that of hydraulic fracturing,and the initiation pressure of SC-CO2 fracturing in sand is about 57.1% lower than that of hydraulic fracturing.Compared to hydraulic fracturing,the pressurization rate of SC-CO2 fracturing is slow due to the compressibility of CO2.Furthermore,the SC-CO2 fracturing in shale has repeated cracking phenomenon,and it is easier to induce complex cracks.With the increase of temperature,the initiation pressure by SC-CO2 fracturing decreases.The CT scanning shows that SC-CO2 fracturing in shale is easier to form multiple network cracks and achieves the similar effect of stimulated reservoir volume. [ABSTRACT FROM AUTHOR]

In order to study the dynamic mechanical properties of northwest artificial frozen red sandstone,the shock compression tests were conducted on red sandstone at -15 ℃ using SHPB apparatus.In the SHPB tests,five groups of valid test data were analyzed,and five stress-strain curves were obtained with different average strain rates.Based on the damage evolution and the component model theory,the frozen red sandstone is considered as a non-uniform particle composed of elastic,damage,plastic and viscous properties.In this paper,a time dependent damage model which includes the damaged body element,the clay pot and the spring is established.It is found that the strength of the specimen is exponentially correlated with the average strain rate.When the average strain rate is low,the strength of the specimen changes gently,and the strength of the specimen increases sharply at the high average strain rate.When the average strain rate is 120.73 s-1,the peak value of stress is as high as 84.96 MPa,which is about twice of the static compressive strength of 44.1 MPa.The time dependent damage model can reflect the stress-strain relationship of the frozen red sandstone in a certain range. [ABSTRACT FROM AUTHOR]

This paper summarizes the engineering practice of longwall top-coal caving (LTCC) in China in the past 35 years,which can be divided into three stages:exploratory stage,promotes application stage,expands stage,mature and output stage.LTCC has become a representative technology and achievement of Chinese coal mining practice around the world.The theoretical research and progress of LTCC are summarized as the stage of reference,the stage of exploration and the stage of innovation.Innovative theoretical achievements in the field of top-coal drawing law are introduced and some directions of the theoretical research of LTCC in the stage of innovation are proposed.For example:the fracture mechanism of top-coal,the drawing law of the loose top-coal,the relationship between the support and the surrounding rock,the strata movement law,the supporting mechanism of full coal roadway,basic economics of LTCC,etc.In-depth theoretical research can further guide the improvement of LTCC technology and expand its application. [ABSTRACT FROM AUTHOR]

The current research on the migration of the proppants in hydraulic fractures and the corresponding flow conductivity are mainly carried out by indoor experiments,though the entirely computer-based research is the tread,yet rare now.In this paper,based on our previous DEM results of proppants in hydraulic fractures,the digital models of the propping agent under different stresses are obtained using digital reconstruction method.Subsequently,based on the digital reconstruction models,the single phase fluid flows through proppants are simulated numerically by utilizing the lattice Boltzmann method,and the absolute permeability values for different proppants and stresses are derived accordingly.Moreover,the numerical permeability coefficients are in good agreement with the empirical Kozeny-Carman formula.The study shows that the higher stresses imply the smaller crack apertures,the tighter proppant packing and the more embedment of proppant.With the increase of stress,the specific surface area increases,and the porosity and permeability reduce accordingly.Under the same stress level,the larger proppant corresponds to the smaller porosity and specific surface area,the easier to and embed,and the larger permeability reduction though generally higher than the smaller proppant size. [ABSTRACT FROM AUTHOR]

The surface-consistent amplitude compensation can attenuate the abnormal response of seismic data caused by the acquisition conditions changing and highlight the response by underground geology.It can improve the exploration precision and resolution.In the actual production,the detectors in the same receiving location will have several different inclined attitudes and different coupling with the soil caused by the construction conditions changes,which will directly make these detectors have several different features about receiving sensitivity and amplitude response.In order to solve this problem that the receiving conditions do not match the surface consistency principle and theoretical assumptions,the paper proposed a new method and technique for surface-consistent amplitude compensation based on the Common Attitude Gather,which is the subset abstracted from a Common Receiving Gather according to the tilt angles of its detectors in different periods of time.It is confirmed through analysis that the receiving condition of a Common Attitude Gather can agree with the surface-consistent more fully.The difference between the new technique and the existing ones is that the Common Receiving Gathers are replaced by the Common Attitude Gathers when implementing.Tests in the model data and the actual production data show that the new technique can effectively solve the surface-consistent amplitude compensation. [ABSTRACT FROM AUTHOR]

China is relatively rich in coalbed methane.A better estimation of maximum adsorption capacity and recovery ratio is based on a better understanding of isothermal adsorption curve.This paper is going to make a comparative study on Langmuir equation,the representative theory of monolayer adsorption theory,and DR equation,which is based on micropore filling theory on an attempt to find a more suitable model fitting equation.Data of the coal sample from four different coal ranks (Ro,max from 0.60% to 3.18%) are fitted.The result shows that VL and pL would be more accurate in physical significance and the equation fitting would be more meaningful if the two parameters are calculated before fitted;the accuracy of other parameters is improved while V0 in DR equation is calculated;and Amankwah method is the most suitable method for calculating p0 after a comparison of five calculation methods by introducing the concept of virtual saturated vapor pressure.DR equation works better in fitting effect and comes nearer to the actual data after a comparison between Langmuir and DR equation. [ABSTRACT FROM AUTHOR]

The calculation method of the sectional area of carrying material section is the key factor to determine the width of conveyor belt,and it directly affects the belt conveyor system financially.This paper reviews and analyzes the development of the calculation method of the carrying material sectional area of belt conveyor.The authors compare and analyze the surface contours of material accumulation and margins in the calculation method of the sectional area of the carrying material section of the current mainstream DIN22101,ISO5048 and CEMA.By means of calculating the sectional area,series expansion,analysis theory and numerical calculation are given,proven that when the structure and material parameters are the same,the theory of sectional area of carrying material from small to large is as follows:the arc calculation formula,DIN22101 calculation formula,ISO5048 calculation formula;The calculation formula of DIN22101 carrying material area is simple,but needs to convert the dynamic repose angle to the equivalent angle;the CEMA (arc formula) calculation method of carrying material sectional area has a larger margin,especially in the case of large belt width,the economy of system is reduced,also the calculation formula is not simple enough;the calculation formula of ISO5048 carrying material has a simple cross-sectional area form,which is recommended in the development of national standards. [ABSTRACT FROM AUTHOR]