| The research object of this paper is the working face coal rock sample of the Henan PingMei Limited company.Temperature and effective stress,especially the influence of temperature on permeability of coal and rock mass are studied from the micro structures,including the pore and the fissure of the coal body.Two tests were carried out in the previous period.One is the permeability test of briquette samples under different temperature and effective stress.The other is the polarizing microscope test for on-line heating and synchronizing the microstructure evolution of raw coal samples.Then SEM scanning is used to observe the micromorphology of the coal sample and the scanning image is effectively segmented.Through different segmentation algorithms(Histogram segmentation,K-mean clustering segmentation,K-mean clustering combined closed operation,K-mean clustering combined with first closed operation and other algorithms),comparison experiments were carried out and contributed to a better segmentation algorithm——K-means clustering combined with the algorithm of pre-opening and closing in mathematical morphology,which facilitates more precise segmentation and quantitative analysis of microscopic scanned images.Thus,through this algorithm,the inherent causes of changes in coal rock permeability under different temperatures and effective stresses can be obtained,providing new ideas for the future study of the microstructure and microscopic permeability changes of coal and rock,and the mining and migration laws of coalbed methane.The test results showed:(1)The coal rock permeability increases first and then decreases with increasing temperature.As the temperature rises,the overall coal sample expands outward,both the size and the number of the percolation channels increase,and the permeability becomes higher.After the temperature reaches 60°C,the permeability tends to be flat with the increasing temperature.(2)The permeability of coal rock shows a single decreasing trend with increasing confining pressure.Under the initial loading stress,the percolation channel of the coal body decreases rapidly and the permeability decreases.The expansion of the solid particles caused by the stress field in the middle is weaker than the expansion of the coal sample caused by the temperature field.The permeability of the coal samples is stable or increases locally,and then slowly decreases until it becomes flat.(3)From the perspective of micro-morphology,the change mechanism of coal rock permeability with increasing temperature is well verified.It was observed that when the temperature increased,coal pores and fissures first expanded,and the percolation channels expanded,leading to a rapid increase in permeability in the early stage of temperature increase;after 60°C,the pores and fissures were reduced by extrusion,resulting in a decrease in permeability.(4)Using K-means clustering combined with the algorithm of pre-opening and closing filter operation in mathematical morphology,microscopic images with indistinct gray areas obtained by SEM scanning are effectively segmented,and the accuracy of the algorithm is verified.The open operation can eliminate the hole noise formed in the area after image segmentation.The closed operation can fill small holes in the object,connect adjacent areas and remove the point noise in the image.Therefore,this algorithm ensure that the noise can be reduced to the lowest level while keeping the SEM scan image segmentation shape unchanged as much as possible.(5)Using K-means clustering combined with the algorithm of pre-opening and closing filter operation in mathematical morphology and starting from the partial scan image face rate,the effect of temperature on permeability was further verified.The face ratios at 20°C,40°C,60°C,80°C,100°C,160°C,200°C,and 240°C were 4%,5%,7%,6%,4%,3%,2% and 2% respectively..The trend of the curve constituted by these values and the penetration rate were basically consistent with the trend of temperature change. |
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