FORMATION ENVIRONMENT OF TRIASSIC EVAPORATE ROCK BASIN AND DOLOSTONE RESERVOIRS IN THE SICHUAN BASIN

The strata thickness from Second Member of Jialingjiang Formation to Leikoupo Formation in the Sichuan Basin is over 1 500 m.It is composed of dolostone,anhydrite,halilith and interbedded limestone,among which the dolostone is one of the main gas reservoirs in the basin.In the early Jialingjiang stage,the mountain system around the Sichuan Basin keeps uplifting,and the base depresses and dips eastwards.Periodically dry and hot weather makes the basin turn from open shelf to constrained basin.In the early-middle Jialingjiang stage,dry and hot weather makes sea water within the basin concentrate.A set of dolostone and anhydrite formation deposits at the lower land of Jiannan and Wanxian.From the late Jialingjiang stage to the Leikoupo stage,the Jiangnan old land uplifts rapidly and compresses northwestward.The underwater uplifts in Qiyaoshan and Luzhou-Kaijiang are formed,which drive the basin to migrate westwards.The basin with deep depression and high salinity is formed and isolated from open sea.A formation association dominated by dolostone,anhydrite and halilith is massively deposited.Locally,there exists glauberite and polyhalite.The dolostone reservoirs develop dissolved pores in addition to inter-crystal pores,and the over-lying anhydrite and salt rocks are good regional cover rocks.