THE TERTIARY OIL SOURCE CORRELATION IN QAIDAM BASIN

Qaidam Basin is a typical Tertiary inland salt lake containing oils and gases.There is a complete sequence of oil maturation: from immature to highmature.Under such background, the oil source correlation, concerning the evaluation of resource volumes in different stages of hydrocarbon generation, is of great importance. According to the analysing data of 35 rock samples and 23 oils and on the basis of the comprehensive geochemical study, the paper discussed the oil souce beds of different ages via biomarkers, the correlation of oils and source rocks in different layers as well as in different evolution stages. GC/ MS analysis was undertaken by Finnigan-Mat YSQ-45 GC-MS-computer system. The methods of oil source correlation include: 1. carbon isotopic composition 2.bulk distribution of cyclic biogenetic compounds 3.distribution of steranes with different carbon numbers 4.combination of source indicators with maturity indicators to discriminate source rocks 5.fingerprint types of oils and rocks The results revealed that methods 1 and 2 can distinguesh the oils of Tertiary sources from those of Jurassic sources. As for the Tertiary oil-source correlation, methods 4 and 5 should be used because the hydrocarbon precusors are stable. The present study suggests that the Tertiary possessed good source rocks; the sterane carbon number distribution of source rocks shows " V" ?shaped fingerprint and C₂₇ predominance. Relatively, the Eocene- Oilgocene source rocks are better than the Miocene rocks, their boundary value of ( C₂₇+ C₂₈) / C₂₉ is 1.6. Our study, in which the oil source correlation was investigated through the whole hydrocabon generation process proved that the hydrocarbons generated in different stages, i.e., crude oils of different maturity, can be correlated to their source rocks.It was confirmed that crude oils found in Qaidam Basin by now are mostly low-mature.However, the mature and high-mature hydrocarbons are rarely found.That means, the basin is still of great resource potential.