关键词: 四川, 盆地, 侏罗系, 油气运移, 含烃浓度, 断层

Abstract: In the southern part of west Sichuan Basin, the Jurassic is composed of red clastic sediments with a huge thickness, having no petroleum generating potential. However, a large number of Jurassic gas reservoirs with small to medium reserves have been found. Based on the groundwork laid by previous researches on the source of these gases, a study was made on the migration
traces through analyzing the natural gas composition, hydrocarbon concentrations in the rocks, light hydrocarbons (C4-C7) in the condensate, and chromatographic features of saturated hydrocarbons from the reservoir extracts. It is concluded that the hydrocarbons were generated in the Xu5source rock of the Upper Triassic, and migrated vertically, via Ziliujing Formation of the Lower Jurassic and then Shaximiao Formation of the
Middle Jurassic, into Penglaizhen Formation of the Upper Jurassic. It is also suggested that the faults enhanced development of fractures and improved connectivity both within and between the sand bodies and promoted vertical hydrocarbon migration. Results of the present work reveal a prosperous domain of exploration for shallow gas reservoirs in the area under study.

Key words: Sichuan basin, Jurassic, vertical migration, sand bodies, faults, shallow gas reservoirs