羌塘盆地南部海相侏罗系古油藏例析

羌塘盆地具有良好的油气生储盖组合。盆地内已发现100多处油气显示,其中最典型的南羌塘坳陷“隆鄂尼古油藏”发现于中侏罗统布曲组,为一被断层切割的背斜构造,出露面积约10km~2。主要储层白云岩累计厚度达400.9m,孔隙度最高达15.5%,渗透率最高达283×10~3μm~2。分析结果显示油苗性质为“轻质油”,具有海相原油的特征,其烃源岩主要为中侏罗统夏里组页岩。据构造及烃源岩有机质热演化史分析,盆地内构造形成和烃类转化的高峰期同处于燕山运动晚期。该古油藏的发现,说明了羌塘盆地内确实发生过油气的生成、运移和聚集过程,特别是在盆地内三叠系一中侏罗统未出露的大量地区,具有良好的油气勘探前景。

A Case Analysis of the Jurassic Marine Destroyed Reservoirs in Southern Part of Qangtang Basin, Qinghai-Tibet Plateau

Qangtang Basin located in the north of Qinghai-Tibet Plateau is the most developed region of Triassic-Jurassic marine strata in China.There are favorable source-reservoir-cap assem- blages in the basin, in which more than 100 oil and gas seep- ages have discovered.The most typical one is the Middle Jurassic Buqu destroyed oil reservoir at Lung'erni in the south- ern part of the basin.It is an anticline cut through by faults and has an exposed area of about 10km~2.The main reservoir rock is dolostone with a cumulative thickness up to 400.9m.The porosity and permeability are high up 15.5% and 283×10~(-3) μm~2 respectively. The analysis of oil components shows that it is mainly light oil and characterized by marine-origin oil that de- rived from the Middle Jurassic Xiali shale.According to the analysis of tectonic evolution and source rock maturity,the time of trap formation is simultaneous with the peak time of hy- drocarbon generation,e.g.during late Yanshanian.The dis- covery of the destroyed Lung'erni reservoir reveals a good ex- ploration prospect because the processes of hydrocarbon gen- eration,migration and accumulation indeed once happened in the basin,especially in the wide area where the Triassic to the Middle Jurassic strata are not exposed