THE GEOCHEMISTRY CHARACTERISTICS AND ACCUMULATION-HISTORY OF CRUDE OIL IN THE BONAN SUB-SAG OF THE ZHANHUA SAG, THE BOHAIWAN BASIN

The 4th member of the Shahejie Formation is the main petroleum reservoir in the Bonan sub-sag,the Zhanhua sag.At present,there are some different points of view about the distribution of the source rocks contributing to this reservoir and the history of hydrocarbon accumulation.According to some geological or geochemical data in the region of interest,including the homogenization temperature of fluid inclusion,the geochemistry characteristics of crude oil,periods of hydrocarbon generation and expulsion in source rocks of the 3th member and the 4th member of the Shahejie Formation,and the evolution of faul-tage,the history of hydrocarbon accumulation in the 4th member of the Sahejie Formation are discussed in this paper.The result shows that the process of petroleum accumulation in the 4th member of the Shahejie Formation is divided into two major phases.The first stage of the accumulation process started at the late stage of E_s²,mainly from the middle period of E_s² to the metaphase of Ed.The second stage was from the initial stage of Ng to the initial stage of Nm,mainly at the middle-late stage of Ng.The process of petro-leum accumulation was discontinuous in the late stage of Ed because of the uplift of stratum in that period.The periods of petroleum accumulation are in consonance with the period of hydrocarbon generation and expulsion in source rocks of the 3th member and the 4th member of the Shahejie Formation.Therefore,it is suggested that the relative contribution of the source rocks of the 3th member and the 4th member of the Shahejie Formation to formation of reservoir mainly depend on the spacial relation between source bed and fault or trap.