塔河油田奥陶系原油有机地球化学特征及其油藏成因

Characteristics of Molecular Geochemistry and Genesis of Crude Oils from Tahe Oilfield of Tarim Basin

塔河油田是我国迄今为止发现的早古生界最大的海相碳酸盐岩型油气田,其油气地球化学特征及成因备受关注,但目前仍然存在诸多争议。通过系统采样和高精度GC—MS分析,精细研究了塔河油田原油的生物标记化合物分布特征,进行了油源对比并探讨了其成因。研究表明:塔河油田原油其具有相似的成因类型,其母质类型为菌藻类;浮游绿藻和宏体褐藻对原油的生成有重要贡献;原油为成熟—高成熟原油形成于海相还原环境;中上奥陶统烃源岩为塔河油田的主力烃源岩,下奥陶统和寒武系烃源岩也对塔河原油的形成做出了重要贡献;原油具有多期成藏的特征,且早期油藏遭受了一定程度的生物降解。这些研究结果为同类油气田的评价、勘探、开发提供了科学依据。

Tahe oilfield locates in the southwest part of Akekule uplift of Shaya uplift in Tarim basin. So far Tahe Oilfield is the largest marine limestone oilfield of China. In spite of abundant geological and geochemical research efforts are carried in the oilfield but some kinds of doubtful points are not resolved for example the main source rocks, parent material and hydrocarbon accumulation period. Oil samples come from new developed oil-wells of Tahe oil-field. According to the systems analysis and high precision GC-MS analysis, this paper studied the distributional characteristics biomarkers, oil and source rock correlation, and genetic type of oils. The geochemical characteristics of saturated hydrocarbon we can know that the oils from Tahe oilfield have higher maturity, kerogen type is homonemeae, the oils form from marine reducing environment, and the oils suffer some kind of biodegradation. The predominance of C29 sterane is related to pelagic green algae and macro body brown algae. The detection of Dinoflagellate sterane and 4- methyl sterane show the contribution of dinoflagellate and bacteria. Trieyclic terpane and tetracyclic terpane parameters show that they are marine crude oils. The maturity of oils from Triassic and Carboniferous are higher than Ordovician crude oils. The distributional characteristics of pentacyclic triterpane indicate the contribution of homonemeae. Gammacerane/αβ-C30-hopane and the content of 〉 C30-hopane show that the oils originated from salinity marine environment. C29-sterane 20S/（20S ＋20R） and [313/（（xct ＋ 1313） are 0.47-0.52 and 0.49-0.58 indicate that the oils are mature crude oils. The main source rocks of Tahe oilfield is a controversial problem. According to the relative content of CzT-, C2sand C29-sterane This paper discussed the source rock of Tahe oilfield. The results show that middle and upper ordovician source rocks are chief source rocks, and also lower Ordovieian and Cambrian source rocks have some kinds of contribution to high-maturity oil. The oil reservoirs have characteristics of hydrocarbon accumulation multi-period. Above the study result will offer scientific reference for the exploration and develop of this kind of oilfield.