南八仙油田下油砂山组地层物源分析

Analysis for the Sources of N 1 2 Oil-bearing Member of Neogene in Nanbaxian Oilfield of Qaidam Basin

利用录井、钻井等的相关资料较为深入的分析了南八仙油田下油砂山组(N12)地层中的重矿物、成分成熟度、砂砾岩厚度分布以及泥岩氧化色。矿物鉴定资料表明南八仙油田由北东至南西向稳定重矿物含量逐渐增高,而且呈现出以"锆石+石榴石+电气石+绿帘石+榍石+金红石"的主要组合形式;ZTR指数范围为0.15～0.36;成分成熟度指数均值为0.77,成熟度低,且均呈现出由北东至南西向,由南东至北西向增大的趋势;砂岩厚度由北东、南东至南西、北西向逐渐变薄;研究区泥岩氧化色在研究层位分布区域广,且沿北东至南西向逐渐减少;下油砂山组(N12)物源主要来自北东方向的祁连山系古老变质岩区,部分来自南东方向构造高点,同时也表明柴达木盒地在该期处于萎缩期。

The study area is located in the northeast of Qaidam Basin.Mineral identification data show that the stable heavy mineral content increased gradually from north east to south west,and presents a form of zircon+garnet+tourmaline +epidote+sphene+rutile ; ZTR index ranges from 0.15to 0.36 ; The average of compositional maturity index is 0.77.It proves that the maturity is low,the ZTR index and maturity index increase from north east to the south west,from south east to north west.Sandstone thickness is more and more thinner from the north east,south east to the south,west and north west.And the oxidation color of mudstone presents wide distribution in the research area,and the content of its oxidation color reduce gradually from the north east to the south west.The result shows that there are two sources for N 1 2 oil-bearing formation,one is the metamorphic rock area of the Qilian Mountain in the north-east of Nanbaxian Oilfield and the other is the area of the south-east of the structure high side of Nanbaxian Oilfield.Besides,it shows that Qaidam Basin is in a fade period during the N 1 2 .And this research is beneficial for studying the process of deposit and for evaluation and exploration of Qaidam Basin.