西藏尼玛盆地古近系牛堡组烃源岩地球化学特征

Geochemical Characteristics of the Paleogene Niubao Formation Source Rocks in the Nima Basin,Tibet

目前青藏高原中-新生代沉积盆地油气资源评价程度相对较低,对有机质来源及热演化过程等研究程度较低。本文以尼玛盆地古近系牛堡组为研究对象,通过对其有机质丰度、有机质类型以及有机质热演化程度的分析,发现尼玛盆地牛堡组泥岩烃源岩有机碳质量分数在0. 52%～4. 14%,平均1. 25%,属中等-很好烃源岩;有机质类型以II1型为主,三件为I型。烃源岩岩石热解峰温Tmax为424～483℃,镜质体反射率Ro为0. 72%～0. 86%,表明有机质演化达成熟-高成熟阶段。综合数据分析表明尼玛盆地牛堡组烃源岩具有较好的生烃潜力。这对认识尼玛盆地的油气勘探价值,进一步突破在青藏高原陆相第三系盆地寻找油气资源仅在伦坡拉盆地中东部概念的束缚,为整个伦坡拉盆地群开展油气勘探工作提供了很好的指导意义。

The evaluation degree of oil and gas resources in the Mesozoic-Cenozoic sedimentary basins of the Tibetan Plateau is relatively low so far.Moreover,the understanding of the source of organic matter and the degree of thermal evolution remains poor.Taking Niubao Formation of Paleogene in the Nima basin as a research object,this paper presents an analysis of its organic matter abundance,organic matte type and organic matte maturity.The results show that the total organic carbon(TOC)content lies in 0.52%~4.14%,1.25%on average,implying a medium-very good source rock.The organic matter is mainly of II 1 type,and three samples belong to I type.The pyrolysis peak temperature of rocks(T max)is 424~483℃,vitrinite reflectance(R o)is 0.72%~0.86%,suggesting the thermal evolution of organic matter had reached a mature-high mature level.Comprehensive analysis of data shows that the Niubao Formation source rock in the Nima basin has a good hydrocarbon generation potential.The above conclusions are useful for estimating the value of oil and gas exploration in the Nima basin,further breaking the yoke of the concept that petroleum-search of the Tertiary terrestrial basins in the Tibetan Plateau is confined to eastern-central part of the Lunpola basin.And it is also instructive to exploration of oil and gas in the entire Lunpola basin.