The Model Of The Coal Accumulation And Coal Reservoir Characteristics In Jurassic Of South Qilian Basin

The southern Qilian basin is located in the northeastern margin of the Qinghai-Tibet Plateau,the north of which adjacent to the Middle Qilian and the North Qilian Mountains,the south of which adjacent to the Zongwulong Moutain-Qinghai Nanshan.The southern Qilian area has been known as the classical area,and its rich geological phenomena and good exposing conditions provide a solid material basis for the study of orogenic belts in China.In view of the actual geological conditions of the southern Qilian basin,the model of coal accumulation,the development and distribution,and the lithofacies palaeogeography of the main coal seam in the basin are analyzed and studied in depth from the core contents of coalbed methane enrichment and accumulation.The model of the coal accumulation and coal reservoir characteristics are defined in the southern Qilian basin.The results show that Muli formation and Jiangcang formation of Jurassic are the main coal-bearing strata in the southern Qilian basin.Braided river-braided river delta sedimentary system is mainly developed in the Muli formation of Middle Jurassic.The braided river delta-lake sedimentary system is mainly developed in the Jiangcang formation of Middle-Jurassic.Thick coal seams are mainly developed in the braided river delta sedimentary system.The study area,Tuolai Mountain in the northeastern and Datong Mountain in the southern,provide major source of resources.The main coal-bearing environment is located in the delta plain peat swamp.It pointed out that the delta plain swamp is the best coal-forming environment.Geological structure,lithology of top and floor about coal seam,thickness of coal seam,geological conditions and composition of coalbed methan and other factors control coalbed methane accumulation the Jurassic System,in which the shape of coalbed methane reservoir are controlled by the structural.Content of coal seam gas are constrainted by the coal roof and floor.The organic matter of coal has a strong ability of generating gas.Organic matter of the Southeastern Jurassic has a greater potential for generating gas,mainly including crack gas.From the vitirnite reflectance and the characteristics of coal evolution,the coal thermal evolution in the northwest is low and the gas potential is too small,mainly including long flame coal and gas coal;Southeast coal thermal have a high degree of evolution and the potential of generating gas is high,mainly including coking coal and lean coal-based;thermal evolution of central coal is moderate and the potential of generating gas is flat,mainly including rich coal.