THE GENERATION AND CHARACTERISTICS OF SOURCE ROCKS IN NANPU OIL-RICH DEPRESSION,BOHAI BAY BASIN

In recent years,oil-gas exploitation has significant progress and Nanpu depression is found as one of the most oil-rich depressions in Bohai bay Basin.Through the exhaustive research,organic-rich source rocks are identified within Shahejie Formation(Es),especially the TOC(total organic carbon)get the peak abundance in Es34 formation and values commonly exceed 5%.During the early Eocene period when major faulted depression movement occurred,lacustrine basin occupied the largest area and water depth arrived at the highest level in history;wide-spread gray,black mudstone,calcareous mudstone and oil shales prevailed over the stage,which were characteristic of magnificent thickness.The second important hydrocarbon source rocks are fine-grain dark mudstone which develop within Es33 formation.Generally,hydrocarbon source rocks verified in the Es~3_3 member are responsible for the most of hydrocarbon generation that is estimated up to 70%.Although Es_1 member is not comparative with Dongying(Ed) formation in thickness,yet on account of the higher evolution degree,the two source rocks approximately provide nearly 15% oil production separately.