四川盆地达川-万县地区下三叠统飞仙关组层序地层特征

he Sichuan Basin is China's largest natural gas producing area. In recent years, gas exploration achieved major breakthroughs in the eastern part of the basin. A number of oil and gas reservoirs, large and medium-sized gas fields, and natural gas prospects have been discovered in Permian and Triassic successions. Oil and gas reservoirs are mainly carbonate rocks of reef and beach facies. To explore reservoir rocks distribution, we applied sequence stratigraphy in the study of the Feixianguan Formation of Dachuan-Wanxian Area in the Sichuan Basin. Based on the Vail sequence theory, combining with the research achievements of core, drilling and seismic data, according to the sequence stratigraphy division of the field section and sequence stratigratic correlation of connecting-well, the Feixianguan Formation of Lower Triassic in Sichuan basin can be devided into 2 third-order sequences and four system tracts: Sq1 representing the 1st and 2nd members,and Sq2 representing the 3rd and 4th members of the Feixianguan Formation. Grounded upon the carbonate platform,both Sq1 and Sq2 are made up of the transgressive and highstand systems tracts and lack of the lowstand systems tract. Stratigraphic correlation shows that in highstand systems tracts are characterized by late platform margin oolitic facies and intra platform oolitic facies. Extensive dolomitization of platform margin oolitic facies led to greater porosity and permeability, hence the formation of favorable reservoirs. This research has implications for further exploration of the Sichuan Basin.