柴达木台南地区第四系细粒沉积岩相与沉积模式研究

柴达木盆地台南地区第四系涩北组为坳陷湖盆中央低缓穹窿状继承性发育地貌环境下的湖泊沉积,沉积地层为弱固结粉细砂岩、泥岩。应用高压氮气特殊取心资料进行岩相研究,研究结果表明,台南涩北组细粒级岩相可划分为7种类型,垂向上有5种组合,进而可划出砂坝、滩砂、泥坪3种水体能量不同的沉积微相。这3种微相有序分布,砂坝在中央低缓穹窿高部位处、枯水面附近集中发育;滩砂于翼部、枯水面以下集中发育;砂坝常镶嵌在滩砂中;泥坪集中于向斜部位,且在湖平面相对上升期全区分布。这3种微相易于区分储层与非储层,并能突出储层非均质性,砂坝物性明显好于滩砂,滩砂非均质性强于砂坝,泥坪既是生物气的物质来源,又形成天然气的渗流屏障。

Research on the Quaternary fine-fraction lithofacies and sedimentation model in Tainan Area,Qaidam Basin

The lacus sediments in Sebei Formation of Quaternary in Tainan Area,Qaidam Basin is developed along one of the growing low-uplifting dome in the center of the depression basin.The sediments are weakly cemented as siltstone and mudstone.Data from core that was cored under sealing high-pressure nitrogen environment were adopted in this study.It is proved that 7 types of lithofacies and 5 types of lithofacies group could be classified in the Sebei Formation of Quaternary in Tainan Area.Accordingly,3 types of microfacies(called energy units sometimes) could be acquired,which are sandbar,mat-stone and mat-mud.These 3 types of microfacies distributed orderly.Sandbars concentrated on the higher position of the dome and close to the low water surface of lacustrine.Mat-stones concentrated on the flank of the dome and under the low water surface of the lacustrine.Sandbars set among mat-stones often.Mat-mud concentrated in the trough bend and could extend to the entire area when the lake surface moved upward relatively.The physical property of sandbars is better than that of mat-stones,and the heterogeneity of mat-stones are better than that of sandbars.Mat-mud acted not only as the biogenesis-gas generating rock but also as the infiltrating barrier wall of the natural gas.