| Hydrocarbons exploration in the Tarim basin, northwest China has been a focus for a long time by the petroleum industry of China. However, influenced greatly by the structural settings of the entire Tarim basin, the Tazhong region had experienced complex evolvement process that characterized by"multi-phase basin forming, multi-phase reconstruction, multi-set of source rocks, multi-phase generation & expulsion, together with migration, accumulation and dissipation of hydrocarbons, etc., which led to the forming process of hydrocarbon reservoirs being extremely complex. Therefore, it is very necessary to study the movement of hydrocarbons with multi-phase filling features during geological periods. Also, a number of questions related to the mechanisms and characteristics of hydrocarbon generation, migration, accumulation and preservation should be investigated systematically to detail the dynamic process for forming hydrocarbon accumulations. And it is not only the significant content of comprehensive research on petroleum geology, but also has become the bottleneck breaking through theoretical investigation in the worldwide petroleum exploration.Guided by the research methods of petroleum accumulation system, by integrating the up-to-date approach and progression of tectonics, geochemistry, petroleum geology, et al., the eopaleozoic multi-source petroleum accumulation system with separate source rocks, reservoirs and capping rocks had been studied by virtue of the advanced measuring and testing techniques in this paper. The research contents include source rocks, migration pathway and the characteristics of petroleum migration and accumulation during the geological periods.The results indicate that the oil/source correlation and analysis of several organic geochemical parameters, together with the hydrocarbon generation conditions, which including the organic phase (faices), organic matter abundance, thermal maturity and expulsion evolvement of source rocks, verified the conclusion that the present hydrocarbons located within the Tazhong region mainly came from the Lianglitake formation, middle-upper Ordovician source rocks dominated by marlite. And the effective source rocks are mainly located within the middle-upper Ordovician formation.The existence of two effective fluid-conduit systems has been confirmed during the geological historical period, while the first type is being controlled mainly by faults that connected oil source rocks and reservoirs, and the other type being dominated mainly by unconformities. Based on the comprehensive study of several maturity parameters and migration indexes, such as the saturated hydrocarbons, the arene and nitrogen compounds, together with the features of microelements within the hydrocarbon inclusions, it is considered that petroleum migration within the pathway systems in the early and late stages are different in different areas. The detailed migration directions are as follows: 1) The migration and accumulation in the late stage. Vertical migration dominated the oil and gas distributions within the northern slope of the structural belt Tazhong-10, which transported the middle-upper Ordovician hydrocarbons to accumulate within the Silurian reservoirs. However, in the Tazhong-â… fault zone (such as Tazhong-16 well field), the middle-upper Ordovician hydrocarbons mainly migrated laterally along the unconformities located between Silurian and Ordovician formations, and accumulated in the structural high part. 2) The migration and accumulation in the early stage. The characteristics of microelements and element groups within single inclusion and group inclusions provide evidences for the direction of early hydrocarbon migration, i.e., early hydrocarbon migrated from northwest to southeast. The abundance of microelements within inclusions in the northern slope of structural belt Tazhong-10, however, is always higher than one within the Tazhong-â… fault zone (such as Tazhong-16 well field).Combined with the study on periods of hydrocarbon accumulation within the Silurian and Ordovician reservoirs of the Tazhong region, two models of hydrocarbon migration have been established, i.e., hydrocarbon migration models of the middle-upper Ordovician mobile oil pools and the Silurian oil pools.Based on the above study, it is the potential for exploration within the Silurian formation of the northern slope of the structural belt Tazhong-10 and the middle-upper Ordovician formation of the Tazhong-â… fault zone.
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