西藏尼玛盆地古近系牛堡组烃源岩生烃潜力及分子地球化学特征

Hydrocarbon Potential and Molecular Organic Geochemistry of Niubao Formation in Nima Basin,Central Tibet

位于西藏中部的尼玛盆地面积约3000km2,与之毗邻的伦坡拉盆地是西藏获得工业油流的唯一沉积盆地,尼玛盆地沥青的发现表明尼玛盆地是具有生、排烃历史的含油气盆地。应用有机岩石学与有机地球化学方法,对尼玛盆地南部牛堡组烃源岩进行了系统研究。结果表明,牛堡组有机质丰度较高、有机质母质主要为藻类,另有少量高等植物的输入,主要为腐泥型(Ⅰ型)和腐殖腐泥型(Ⅱ1)型;主要形成于缺氧,盐度较高的咸水湖泊环境,有机质成熟度中等,在生油窗内,经历了2～3级的生物降解作用。因此,结合其它有机地球化学参数,认为牛堡组烃源岩具有较好的生油潜力,对于尼玛盆地油气勘探具有重要意义。

The Tertiary Nima Basin in center Tibet covers an area of about 3000 km2 and is closely similar to the nearby Lunpola Basin from which commercial oils have been produced. The Paleocene-Eocene Niubao Formation is one of the most important hydrocarbon source formations. Although it has good petroleum preservation conditions, the Nima Basin received little petroleum study so far. The comprehensive organic petrology and organic geochemistry studies of hydrocarbon potential and molecular organic geochemistry in the Niubao Formation indicated that algae together with a few inputs from higher plants are the main contributions of its organic matters. The organic matters, which are classified as oil-prone type I and type Ⅱ1 , were formed in the anoxie high salinity environments.