Geochemical Characteristics of Es_3~4 Source Rocks and Its Oil-source Contribution in Nanpu Sag,Bohai Bay Basin

The Nanpu sag is one of the oil-rich depressions in the Bohai Bay basin.The 4th section of the 3rd member of the Shahejie Formation(Es43) is the organic-rich source rock,playing a very important role in hydrocarbon generation in the Nanpu sag.The contribution of Es43 source rocks to petroleum reservoir has been discussed in this paper by evaluating source rocks and analyzing the geochemical features.The results show that the Es43 source rocks have good generation condition with high organic carbon and good type of kerogen.The Es43 source rocks are classified into two types.The first type source rock is mature,deposited in a reducing environment,and originated from ordinary aquatic organisms and higher plants;the second type source rock is immature,deposited in a oxidation environment,and originated from primarily higher plants with minor contribution for oil accumulation.Oil-source correlation shows that the oil in the Shahejie Formation in the Gaoliu area sourced from the type I source rock.