Study on coal facies evolution law of Permian coal seam in south Pingdingshan Coalfield

The coal formed based on different sedimentary environments has great differences in micro-composition and reservoir physical properties.In order to find out the impact of the sedimentary environment on the reservoir physical properties in the subsequent research,different coal seam samples were collected and analyzed by using optical microscope,and the coal facies of Permian coal seam in southern Pingdingshan Coalfield was analyzed and studied.The results show that the microscopic composition of coal seam in the southern area of Pingdingshan Coalfield is dominated by vitrinite group,and the main minerals are clay minerals and pyrite.According to the differences between different coal facies parameters,the coal facies in the study area are divided into five types: shallow-water covered forest swamp,wetland herbaceous marsh,shallow-water covered wetland herbaceous marsh,moist forest marsh facies,and low-level marsh.The depositional environment of Geng20 coal seam changed from wetland herbaceous marsh to low low-lying marsh and then to shallow-water covered forest marsh; Ji15 coal seam changed from bottom wetland herbaceous marsh to middle-upper part shallow-water covered wetland herbaceous marsh.The Wu8 coal seam changed from a wetland herbaceous marsh at the bottom to a moist forest marsh,then to a wetland herbaceous marsh,and finally into a shallow-water covered forest marsh.