The Characteristics And Utilization Of Residual Resources In Closed Coal Mines In Yangquan Mining Area

As an important coal production base in Shanxi Province,the number of closed coal mines has been increasing year by year due to the influence of the optimization and adjustment of energy structure,industrial transformation and upgrading,resource exhaustion and other factors.There is still a considerable amount of residual coal resources,coalbed methane resources,mine water resources and underground space resources in closed coal mines.Secondary utilization can reduce resource waste and promote urban economic development.Taking 75 closed coal mines in Yangquan Mining Area of Shanxi Province as the research object,this thesis explores the occurrence characteristics of the residual coal,coalbed methane,mine water and underground space resources of the closed coal mines in Yangquan Mining Area by means of data collection,sample collection,experimental testing and comprehensive analysis,predicts the amount of resources,and puts forward the direction of resource reuse based on the characteristics of the closed coal mines.The main research conclusions are as follows:（1）Protective coal pillar is the main type of residual coal in closed coal mine of Yangquan Mining Area.The coal quality of each coal seam in Shanxi-Taiyuan Formation is good,the moisture content of raw coal is less than 1.80%,the ash content is between 6.46%and 33.12%,the total sulfur content of each coal seam is less than2.45%,and the main body is between 1%and 2%.According to the block method,the remaining coal resources are estimated.The results show that:The total amount of residual coal resources is up to 106,121 wt,among which the amount of residual coal resources in closed coal mines before merger and reorganization is up to 55153.17wt,and that in closed coal mines during merger and reorganization is up to 19191.76wt.The amount of remaining coal resources in 9 closed coal mines with complete data was31776.07wt,accounting for 36.13%,among which,the coal pillar resources protected by roads and villages amounted to 22327.4 wt.（2）Coalbed methane（CBM）resources in closed coal mines can be divided into goaf CBM resources and in-situ CBM resources.The CBM in goaf mainly exists in the pores-fractures in the goaf in a free state.The 3DEC numerical simulation results show that after the mining of No.15 coal seam,the mining-induced fractures extend far,resulting in vertical multi-layer goaf connectivity.In situ CBM exists in the pore and micro-fracture of coal reservoir in the adsorption state.The porosity of No.15 coal seam is between 3.68%and 4.81%,and micro-nano gas pores and mineral pores are mainly developed.On the whole,micropores smaller than 2 nm are very developed,and mesoporous and macroporous development degree is low.The resource composition method and the volume method are used to predict the goaf CBM resources and the in-situ CBM resources.The results show that the goaf CBM resources and in-situ CBM resources in the closed coal mine are 3.33×10⁸ m³ and 10.78×10⁸ m³,respectively.Nanzhuang and No.3 Coal mine have the most resources.（3）The difference of conventional chemical components of mine water samples from mined coal mines and closed coal mines is compared.The difference of p H value between the two types mine water is small,which is neutral to weakly basic,while the difference of TDS value is large.The TDS of Nanzhuang is the smallest,which is 430mg/L.The cation content of mine water in mining coal mine is ranked as Na⁺+K⁺>Ca²⁺>Mg²⁺,while the cation content of mine water in closed coal mine is ranked as Ca²⁺>Na⁺+K⁺>Mg²⁺.Piper three-line diagram is used to analyze the hydrochemical type of mine water in closed coal mines.When the percentage of SO₄^2-and HCO₃^-in Beiyan and Nanzhuang coal mines is greater than 25%,the hydrochemical type of the former is HCO₃·SO₄-Ca·Mg,and the latter is HCO₃·SO₄-Na.The water resource availability of 9 coal mines with overcapacity reduction and closure is estimated,with a total of 7.24×10⁷ m³.Yangquan No.3 Coal Mine has the largest water resource availability,reaching 3.67×10⁷ m³,followed by Nanzhuang Coal Mine,which is 9.56×10⁶ m³.（4）The underground space of closed coal mine can be divided into shaft space,roadway space,chamber space and goaf void space.According to the average section area of mine shaft and roadway of different sizes,combined with the mine development plan,the length of shaft and roadway is measured and the volume of shaft and roadway is calculated.The goaf void space is calculated according to the surface subsidence coefficient and rock expansion coefficient.The total space resources of the 9 de-capacity closed coal mines with complete data are 704.66×10⁴ m³,and the void resources of the goaf are 72.24×10⁷ m³.On the whole,the underground space resources are concentrated in Nanzhuang Coal mine and No.3 Coal mine,and the underground space depth is relatively shallow,with the main body located below 300 m.（5）The residual coal resources of the closed coal mine in Yangquan Mining Area are mainly protective coal pillar resources,which are not suitable for underground coal gasification and the value of restart and reuse is limited.There are various CBM utilization and extraction modes in closed coal mines.For high-gas closed coal mines with limited resources such as Fuxin,Taichang and Yanshi,low costed drilling and negative pressure extraction are carried out in the rich areas of goaf CBM resources.For the goafs of No.12 and No.15 coal seams of No.3 and Nanzhuang Coal Mine,large-scale negative pressure extraction of surface vertical well and L-shaped well can be carried out.The water inflow of closed coal mine is low,and the water quality index is not very ideal.It is suggested that mine water should be used as industrial water after simple treatment.No.3 and Nanzhuang coal mine have abundant underground space resources,more concentrated shaft layout,goaf,shallow burial depth,simple geological structure,suitable for industrial tourism development and space energy storage and utilization.