Analysis Of Sedimentary Facies And Coal Accumulation Characteristics Of Longtan Formation In Chongqing Songzao Mining Area

The late Permian longtan formation in Songzao mining area of Chongqing is located in the transition zone between the southeastern margin of Sichuan basin and the plateau of Guizhou province.The study area suffers from frequent cutting,weathering,dissolution and denudation of yangfork river and maliu river all the year long,resulting in a topographic landscape that slopes from west to east locally.In the process of coal seam exploration of longtan formation in the study area,it is found that it contains abundant coal resources.However,previous studies on this formation are relatively weak,especially on sedimentary facies.A series of problems,such as unclear distribution of facies belts and unclear paleogeographic characteristics,restrict the advancement and development of coal seam exploration in longtan formation,Songzao mining area,Chongqing.Therefore,this article use the longtan group in the study area of the single well data and previous field profile data,take the single factor analysis and multifactor comprehensive mapping method,combined with the analysis of sedimentary facies of typical Wells and well tie compilation of sedimentary facies,the phase in the longtan formation characteristics of sedimentary system,sedimentary facies analysis and palaeogeographic characteristics analysis,at the same time a preliminary evaluation of the longtan group in favor of the development zone of coal accumulating.Through comprehensive analysis,it is concluded that the sedimentary environment of the upper Permian longtan formation in Songzao mining area of Chongqing is changeable,and the rock types are complex.According to the palaeogeographic map of Longtan period and the coal seam isopachy map,it is believed that a coal accumulating center was developed in the south and north of the study area in the early stage of Longtan formation?P₃l¹?,but the continuity of the coal seam is poor in the horizontal direction.In the middle stage of longtan formation?P₃l²?,the seawater intrusion rate is consistent with the material source supply rate,and peat plateau is preserved.Therefore,three coal-rich belts with large thickness and wide distribution are developed on it.Therefore,these regions are considered as favorable reservoir development zones and can be used as key exploration zones in the next step.In the late stage of longtan formation?P₃l³?,rapid rise of sea level made it difficult for coal-forming plants to grow and peat accumulation was blocked.During this period,most coal seams were thin and discontinuous.Based on the analysis of the coal-forming environment and coal-forming factors in the late Permian of the study area,it is found that the formation of rich coal belt and thick coal seam originates from the coupling of paleostructure,seawater advance and retreat and sedimentary environment.