Geochemical Characteristics and Hydrocarbon Generation History of Paleocene Source Rocks in Jiaojiang Sag, East China Sea Basin

In order to understand oil and gas exploration potential of Jiaojiang sag in the East China Sea basin, hydrocarbon generation capacity and process of the Paleocene Yueguifeng (E₁y), Lingfeng (E₁l) and Mingyuefeng (E₁m) Formations were investigated using geochemical analysis and basin modeling. Results show that E₁y and E₁l mudstones are high-quality source rocks with high organic matter abundance and type Ⅱ kerogen, which is dominated by both aquatic organisms and terrestrial higher plants deposited in sub-reduced environment. E₁m mudstone interbedded with thin carbonaceous mudstone and coal is poor-quality source rock with low organic matter abundance and type Ⅲ kerogen, whose organic matter was derived from terrestrial higher plants under oxidized environment. Great subsidence and high paleo-heat flow from the Paleocene to the Eocene made it main period for increasing thermal maturity of source rocks. Controlled by burial and maturity histories, the E₁y and E₁l formations experienced two hydrocarbon generation stages, which took place in the Late Palaeocene and in the Middle to Late Eocene, respectively, and is characterized by high hydrocarbon generation potential. The E₁m Formation only had one hydrocarbon generation process at the end of Eocene, which is characterized by low hydrocarbon generation potential. The Paleocene source rocks in the Jiaojiang sag have strong hydrocarbon generation capacity, so the future oil and gas exploration should focus on hydrocarbon generation center, especially that of the E₁y Formation, and select effective traps formed before the Miocene.