Gas Seepage Characteristics Of Broken Coal In Ponding Goaf Of Abandoned Mine

With the end of coal mining and abandonment of minable coal seams,the continuous desorption of residual coal leads to the accumulation of a large amount of coalbed methane in the goaf.The fracture zone formed by coal mining activities in the upper part of the goaf leads to the connection between the overlying aquifer and the goaf.After the mine is abandoned,a large amount of water gushes from the aquifer to the goaf to form water in the goaf,which seriously affects the surface drilling and extraction effect of coalbed methane in the goaf with water in the abandoned mine;In this paper,the method of combining physical experiment and field measurement is used to study the co MPaction of broken coal body in ponding goaf of abandoned mine,and the gas seepage law of broken coal body with static ponding and dynamic ponding.Based on the above research,the technical idea of integrated drainage and gas production is put forward;The main research results are as follows:The broken coal in the abandoned goaf is co MPacted and broken under long-term load.The co MPaction and breaking law of the broken coal under the condition of ponding is studied by using the method of physical experiment,which reveals the law that the ponding in the abandoned goaf promotes the co MPaction and breaking of coal,It is determined that the larger the coal sample size is,the more obvious the promoting effect of ponding on coal fragmentation is and the greater the stress is,the smaller the difference between the quantitative results of coal co MPaction experiments with different block sizes is.The long-term load co MPaction of the broken residual coal in the goaf leads to the change of the gas seepage channel in the goaf.Based on the multiphase flow seepage experimental system in the confined space,the gas seepage law of the static ponding broken coal in the goaf is studied by using the physical experiment method.Under the condition of the same ponding volume,the gas permeability of the coal decreases exponentially with the increase of the load,and the coal strain increases with the increase of the load,When the load reaches a certain value,the influence of coal sample size on gas permeability can be ignored,and the load stress becomes the main factor affecting gas permeability.The gas seepage law of ponding broken coal under goaf drainage conditions is studied by physical experiment method,and the co MPaction and gas seepage law of ponding broken coal under goaf drainage conditions are revealed;During the drainage and mining conditions,the secondary ponding in the diversion chamber caused the unstable change of ponding amount,resulting in the unstable change of stress-strain of the broken coal.Co MPared with the static ponding,the permeability change of the broken coal gas seepage experiment is less different.The secondary ponding phenomenon weakens the influence of the initial ponding amount on the gas permeability of the broken coal sample.Under the same ponding amount,the larger the block diameter,The smaller the ratio of gas permeability between ponding broken coal and static ponding broken coal under drainage and mining conditions.Aiming at the problem of water gushing and ponding blockage of surface gas drainage drilling in ponding goaf of an abandoned mine in Shanxi,based on the above physical experimental research and analysis,the technical idea of integrated drainage and gas production is put forward.After the application of the technology,the gas drainage flow is increased by about 30%,the ponding in the goaf is reduced,the gas permeability in the goaf is increased,and the gas drainage concentration is always maintained at more than 85%.The application of the integrated technology of drainage and gas production realizes the high-efficiency drainage and utilization of gas in the goaf with ponding in the abandoned mine.