| Coal seam permeability is the most important factor affecting the efficiency of coal drainage.The results of the study at home and abroad show that the coal seam permeability has natural anisotropy,and the anisotropy of permeability is universal,that is,the original permeability of most coal seams has anisotropy.In this paper,the permeability of different directions is measured by directional sampling,and the anisotropy of coal permeability and stress sensitivity is investigated to determine the direction of permeability.The influence of coal anisotropy on the gas pre-pumping of coal seam is studied by numerical simulation and field test,and the advantageous orientation of drainage and drilling is determined,which provides the basis for improving the gas pre-pumping effect.In this paper,the characteristics of the coal seams and the characteristics of fissure development in the west of Zhengyi Lane,the North Third Road and the North 7 Lane in the 8 # coal seam of Jingjing Mine are analyzed.The west is passing through an anticline structure,and the roadway and the anticline are approximately vertical.The structure of the coal seams in the three main lanes is complicated,and there are two large collapse columns on the west side of the roadway,which leads to the irregular distribution of the coal seam.The north side of the north side of the road through an anticline structure,roadway and the anticline axis is almost vertical.The structure of the coal seams in the seven alleyways is relatively simple.According to the relationship between coal seam formation and fracture distribution,it is found that the fractures of the seven seasons are developed along the northeast-southwest direction.According to the relationship between the coal seam and the distribution of fractures,the west fissures of the west and the west side of the west lane are distributed along the northeast-southwest direction.The fissures of the anticline are developed along the east-west direction,And the fissures of the anticline of the anticlinal axis develop along the east-west direction,and the east side of the anticline is developed along the east-west direction.North seven alley and north septum fissure along the northeast-southwest direction development.The results show that there are few differences in the industrial analysis parameters of the coal samples in the three sites of the West Yixiang Lane,the North Third Road and the North 7 Road,and the results are not very good Sex.The water content of the dry coal base,the dry basis of the ash,and the dry ash are slightly larger than those of the west and the west,The fixed carbon content of the secondary coal sample is slightly larger than that of the north.The actual visual density test results of coal samples in three sampling sites are not very different and have good agreement.In general,the true density and apparent density of the coal samples in the north seven are slightly higher than the true density and apparent density of the coal samples in the west and the third.The adsorption constants of coal samples in three sampling sites have a certain heterogeneity.The adsorption constants of the coal samples in the north seven are the largest,and the coal samples in the north are the second.The adsorption constant of the coal samples in the west is one of the largest,the second coal mine is the second,and the coal samples in the north are the smallest.The original gas content of the coal seam in the three sampling sites has a certain heterogeneity.In the three sampling sites,the original coal seam in the west one is the largest coal content,and the water content of the original coal seam in the north of the north is the smallest.The average coal seam gas pressure is 0.915 MPa,the gas pressure of the original coal seam is 0.67 MPa,and the gas pressure of the original coal seam is 1.03 MPa.The pressure of the gas near the north seven lanes is higher than that of the west and the third lane.The permeability coefficient of the coal seam is 0.106 m2 /(MPa2 · d),and the permeability coefficient of the coal seam in the North West Road is 0.127 m2 /(MPa2 · d).The permeability coefficient of the coal seam near the north seven lanes is the largest,and the permeability coefficient of the coal seam near the west one is the smallest.The results show that the BET ratio of surface area is the largest in the west,and the coal samples in the north are the smallest.BJH total pore volume of the West is a Lane,North seven Lane,North three lane three coal samples are equal;the average pore size of the North Road,the largest number of coal samples,the first seven coal seams,followed by a small coal mine.West Yixiang Lane,North seven alley,North three lanes three coal sample microporous total volume equal.Through the distribution curve of coal sample pore volume,it is found that there are a lot of micro-porosity in the three coalesters of the West-Lane,the North Seven Lane and the North Third Lane.The pore size r is the largest in the range of 0 ~ 5 nm,and 95% Concentrated in the range of 0 ~ 15 nm,is conducive to the occurrence and adsorption of CH4 in coal.It is found that the nitrogen adsorption and desorption curves of the No.3 alley and the north coal seams have not coincident with the desorption curves,and the adsorption hysteresis appears.The results show that the pore-shaped pores in the coal are more developed and the pores are mostly closed by one end Impermeable pore composition.West Yixiang coal samples appear G point,indicating that the coal hole system is more complex,and large holes both open and closed.The permeability of the three groups of coal samples was measured by using the directional sampling device,and the cylindrical coal samples were taken along the coal seam direction,inclination and vertical direction respectively.The anisotropy characteristics of coal seam permeability and stress sensitivity were obtained.The permeability of the coal seepage is the largest,The stress sensitivity coefficient of the coal seam and the tendency of the coal sample is close to isotropic,which is lower than the stress sensitivity coefficient of the coal sample permeability in the vertical direction.The reason why the permeability sensitivity of the coal permeability is anisotropy.Modulus and porosity have anisotropy.Based on the theory of elastic mechanics and seepage mechanics,the creep and exponential of the evolution model of orthotropic coal seams are established considering the anisotropy of coal seam fissure structure,mechanical properties,adsorption / desorption deformation and geostress field.Type expression,and the two sets of model expressions are in good agreement with the permeability data in the published literature.Based on this model,the main influencing factors of coal seam permeability are the anisotropy of effective stress and initial permeability.The effective stress is the differential stress of geostress and gas pressure.The geostress has anisotropy and the gas pressure is isotropic.Therefore,the anisotropy of geostress will be one of the advantages of influencing coal seam permeability.The anisotropy of the initial permeability reflects the anisotropy of the crack structure of the coal seam.The crack structure of the coal seam also has a great influence on its permeability.The same coal sample measures the permeability and the direction of the permeation pressure under the same conditions.The fissure plane of the coal sample is perpendicular,and the permeability is the smallest.The direction of the osmotic pressure is the highest if it is parallel to the fracture surface of the coal sample.Based on the above-established evolution model of anisotropic coal seam permeability,a theoretical model of coal seam gas flow considering permeability anisotropy is established.The COMSOL Multiphysics numerical simulation platform is used to analyze the parameters of the pre-pumping coal seam in the bedding drilling,Modulus,Langmuir adsorption strain constant,initial porosity and initial permeability anisotropy on the pre-pumping seam gas in the bedding layer;the influence of the simulated permeability on the pumping flow under the anisotropic condition The The results show that the anisotropy of elastic modulus,Langmuir adsorption deformation constant and initial porosity have no significant effect on the simulation results,and the anisotropy of initial permeability has a significant effect on the simulation results.When the drilling and drilling When the maximum direction is the vertical direction,the pumping flow is the largest,and the pumping flow decreases with the decrease of the angle between the drilling and the maximum direction of the permeability.When the angle between the drilling and the maximum direction of the permeability is more than 60 °,The effect of the flow rate on the pumping flow is more significant.The greater the permeability anisotropy,the more significant the effect of the hole orientation on the pumping flow.Therefore,the anisotropic characteristics of coal seam permeability should be accurately measured in order to provide a reliable basis for theoretical analysis and numerical simulation.The influence of coal seam permeability should also be taken into account in numerical simulation of borehole drilling.The basic research of the above model analysis,experimental study and numerical simulation has initially determined the reasonable principle of perforating the coal seam gas pre-drilled hole: the drilling should be as vertical as possible with the maximum permeability direction.For the test site,the maximum permeability direction is parallel to the coal seam.In order to verify this principle,five groups of different experimental drilling holes were arranged at the test site,and the influence of the orientation on the pumping flow was measured.The results show that the pumping flow is significantly higher than that of the coal seam(<30 °)when the angle between the borehole and the coal seam is larger(> 60 °),and the above basic research And the principle of reasonable hole in the coal seam gas pre-pumping drilling is determined.In addition,in order to solve the problem that the permeability of 8 # coal seam in Xinjing Mine is low,the flow rate of single hole is small and the flow rate is difficult to be observed,the device for accurately measuring the flow rate of single hole is designed and designed.Accurate measurement and accurate prediction of pre-pumping period.By adjusting the drilling direction,the new prospecting mine can improve the single-hole gas extraction and accumulated gas extraction,accelerate the decay rate of coal gas content,shorten the gas pre-pumping period,reduce the coal seam gas pre-drilling The number of holes arranged,save drilling construction costs,speed up the progress of mining face,improve the efficiency of recovery,increase mine income.By pre-pumping the coal seam gas,the gas emission in the mining process is reduced,the safe mining of the working face is reduced,and the probability of the occurrence of the gas accident is reduced,which is of great significance to the safe production of the whole mine.In this paper,the anisotropy of the permeability of 8 # coal seam in Xinjing Mine of Yangquan Mine is obtained.However,the anisotropy of coal seam permeability in other coal seams and other mining areas of Yangquan mining area needs to be further investigated.In particular,some of the strong coal seams in the geological tectonic zone,the original fissure structure has been destroyed by geological effects,the permeability of these coal seams have anisotropy remains to be verified.The results show that the advantage of 8 # coal seam permeability in Yangquan mining area is parallel to coal seam,indicating that the anisotropy of coal seam permeability is related to coal seam.In general,the coal seam in the working face is heterogeneous,that is,the coal seam in different positions of the working face is different.Therefore,if the anisotropy of the permeability of the coal face in the target face is related to the production,the orientation of the mining hole should be adjusted with the change of the coal seam to achieve the optimal extraction effect.In this paper,the influence of anisotropy on permeability of coal seam is discussed and studied.The accurate determination of the plan,the design of the cloth hole,the prediction of the extraction period and so on need further study. |
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