Abstract:

It is generally believed that light oil is often found at the lower part or the central of an oil pool while heavy oil is more often located at the upper part or the periphery.However,the oil density distribution in the Chepaizi Uplift of Junggar basin proves otherwise:light oil is on top of heavy oil.Oil-source correlation and research on the regional structures,source rock evolution and preservation conditions indicate that multiple types of the Permian and Jurassic source rocks have generated and expulsed hydrocarbon sin several stages in the study area.Multiphase structural activities and sedimentation formed cap rocks of different sealing capacities.It is multiphase reservoiring and different sealing conditions in each reservoirng phase that caused the inverted sequence of light and heavy oil in the Chepaizi uplift.And later injection and certain preservation conditions are consi-dered necessary for forming light oil pool in the Neogene Shawan Formation of the uplift.It is suggested that exploration of the area shall take the possibility of "light oil on top of heavy oil" into consideration.

Key words: distribution of inverted sequences, light and heavy oil, accumulation mechanism, Chepaizi Uplift, Junggar Basin