The Development and Distribtuion of the Triassic Bank-Microfacies in the 2-Section of Jialingjiang Group and Its Gas-Poal Control Nature in the Eastern Part of Sichuan Basin

Key words: 
• Sichuan basin /
• Triassic /
• Jialingjiang Group /
• bank /
• microfactes /
• gas-pool

Abstract: The 2-section of Jialingjang Group of Triassic in the eastern part of Sichuan Basin is an important gas bearing position. The Development of bank-micro factes have played an important pole in controlling the gas pool of fracture-pore type in traps.The banks are POint-bank on the platform in upper yangtze epicontinental sea. The new classificantion of shallow-sea bank and shallow exposed banks has been suggested on the basis of the evolution model of depositional environments which were controlled by relative sea-level changes. The similarities and difference of two types of banks have been compared. There were four bank development periods in the multicycle sedements of 2-section of Jialingjiang Group.The distribution of banks in two bank-development periods, for example, the 2-subsection of 2-section, have been mapped. The composition and devolopment model of point-bank at the Tishan anticline has been analysed. It clearly points out that the lithic factes in the core of bank have big thickness and good continuity in the multi-bank development periods. There are three types of factes sequences models:(1) the banks developed with sea-level up and disappeared with sea-level down; (2) the banks developed with sea-level down and disappeared to expose ; and (3) the banks developed with sea-level up and disappeared with sea-level up.Finally, the authors state how the shallow exposed bank control the formation of gas-pool. It has been recognind: ①the bank-microfacies complexs are beneficial for complexs of oil-producing, reservoir and seal formations, ②the shallow exposed bank is the microfacies zone of the pore-layers devolopment, ③ the sediment-diagenetic trap formed in bank-microfacies zone is beneficial for early accumulation of oil and gas pools @the development of pore-layers and accumulation of oil and gas in early sediment-diagenetic traps are the base of present gas -pool of fracture-pore type in various traps.