四川盆地三叠纪蒸发岩盆地形成环境及白云岩储层

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

四川盆地中、下三叠统嘉陵江组二段—中三叠统雷口坡组厚达1 500 m以上,主要为白云岩、硬石膏岩和石盐岩,夹少量石灰岩地层组合,其中白云岩是盆地内天然气主产层之一。嘉陵江初期,四川盆地周边山系不断隆升,基底下陷东倾,周期性干热气候促使盆地由开放陆棚向局限盆地转变。嘉陵江早中期,干热气候使盆内海水浓缩,在建南及万县等地形较低处沉积白云岩—硬石膏岩地层。嘉陵江中期—雷口坡期,江南古陆急剧隆升、向西北挤压,七矅山、泸州—开江水下隆起相继形成,迫使盆地不断向西迁移,形成深坳陷高含盐盆地,并与外海隔绝,广泛沉积以白云岩—硬石膏岩—石盐岩为主的地层组合,局部见钙芒硝岩和杂卤石岩。白云岩储层除发育晶间孔外,亦有溶蚀孔隙,其上覆膏盐层是良好的区域盖层。

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.