Distribution and Composition of Biomarkers in Crude Oils from Different Sags of Beibuwan Basin

Key words: 
• Beibuwan Basin /
• crude oil /
• biomakers /
• 4methylsteranes /
• oleanane /
• diahopanes /
• diasteranes

Abstract: Various biomarkers in some typical oils from different sags, Beibuwan Basin, have been analyzed, in this paper. The results show that the crude oils from Weixinan Sag and Wushi Sag in the northern basin have relatively lower Pr/Ph ratio, low abundance of oleanane and various rearranged configuration biomarkers, but higher abundance of C26+ long chain tricyclic terpanes with normal pattern in C23 highest peak and C30 4methyl steranes, indicating that their source rocks were deposited under relatively deep and reduced environment with significant algae input. Bun for the crude oils from Fushan Sag and Maichen Sag in the southern basin, it is characteristic of relatively higher Pr/Ph ratio, higher abundance of oleanane and various rearranged configuration biomarkers, but lower abundance of C26+ long chain tricyclic terpanes with steplike decreasing pattern of C19—C26 and C30 4methyl steranes, showing that their source rocks were deposited under relatively shallow and oxidized environment with significant organic matter input from angiosperms. It implies that for northern sags and southern sags in Beibuwan Basin, there are some obvious differences in the depositional environment and organic matter input.