Petroleum Generation History of Lower Tertiary Source Rocks from the Bozhong Depression of the Bohaiwan Basin

There are mainly two sets of source rocks in the Bozhong Depression of the Bohaiwan Basin: Es 3 source rock and Ed 2 source rock. Since the source rocks in the most area of the depression are buried with a great depth, little work on petroleum generation pattern and history of the source rocks have been done. In this paper, a petroleum generation modeling method which is based on hydrocarbon generation kinetics was applied to investigate petroleum generation history of the source rocks from the depression center and the slope area. The results have shown that the Es 3 source rock from the depression center was matured to the main stage of oil generation and the main stage of gas generation occurred over stage of 20～14 Ma and 15～10 Ma, respectively. The Ed 2 source rock from the depression center passed its oil window during 10～5 Ma, and has a present maturation level of gas peak generation stage. In the slope area of the depression, the situation is quite different. The Es 3 and Ed 2 source rocks entered the main stage of oil generation during 10～5 my and after 2 my, respectively, and the current maturation level of the Es 3 source rock is still in the main stage of gas generation. With the combination of reservoir-cap features, and trapping, migration and accumulation conditions in this depression, it was believed that the oil and gas pools discovered around and inside the depression was related to petroleum generation from the source rocks after 10 my, and the source areas include Es 3 source rocks from the slope area and Ed 2 source rock throughout the depression. The Es 3 source rock from the depression center has a contribution to natural gas accumulation in oil and gas pools.