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

Key words: 
• Tahe oilfield /
• Shaya uplift /
• biomarkers /
• maturity /
• oil and source rock correlation

Abstract: 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 C29 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. Tricyclic 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C30hopane and the content of >C30hopane show that the oils originated from salinity marine environment. C29sterane 20S/(20S+20R) and ββ/(αα+ββ) 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 C27, C28 and C29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 Ordovician 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.