Research On The Permeability Variation Of Protected Coal Seam Under The Condition Of Mining

Huainan-Huaibei mining area is an important coal energy base of China. The coalmeasures stratum experienced complex tectonic movement. The coal seam with thecharacteristics of complex structure, high gas content, high gas pressure and lowpermeability.Therefore the direct extraction of coal seam gas is difficult. Because of theworking surface mining,both of the gas pressure and the permeability of the adjacent coalseam are changed, providing favorable conditions for adjacent coal seam gas drainage.InHuainan-Huaibei mining area,suface hole drainage coal seam gas has become an impotanttechnical means for mining Protection Layer.Although there is a lot of engineering experiencein Huainan-Huaibei mining area,but the law of the surface hole drainage parameters andpermeability is lake of research.In this paper,the surface hole drainage dates in Huainan-Huaibei mining area is collectedwidely,and we take experiment in Taoyuan Coal Mine.The research has found out thevariation law about the amount of drainage gas,the concentration of drainage gas and the flowpressure down hole.Before the working surface reach the well,the flow pressure down holefirst increases rapidly then decreases rapidly,the amount and the concentration of drainage gasis very small or near zero.When the working surface reach the well,the flow pressure downhole decreases rapidly,the amount and the concentration of drainage gas increasesrapidly.When the working surface has pushed through the well of about forty meters, the flowpressure down hole is near zero, both of the amount and the concentration of drainage gasincrease to maximal values.And then, along with the working surface pushing continually tillto one hunderd and sixty meters,the flow pressure down hole increases slowly and steadily,theamount and the concentration of drainage gas decrease steadily to stable values.According tothe characteristic of the amount of drainage gas,the interval of production history matching is divided into six regions.The research state clearly that each regional permeability of protectedcoal seam is different,dozens of times or thousands of times. The results of the simulationshow that the permeability of of protected coal seam in mining area is positive with theamount of drainage gas,but negatively with the distance from well to working face.The conclusions draw in this paper are of importance for the suface hole drainage coalseam gas in Huainan-Huaibei mining area.At the same time,the conclusions are significanttheoretical basis for the Important Project of Science and Technology in Developing Great Oiland Gas Field and Coal Bed Methane Coal Bed Methane Production Calculation in CoalMining Areas.