Research on thermal evolution and hydrocarbon expulsion history of source rocks in low-exploration basins：a case study on Jiaojiang Sag, East China Sea Basin

In low-exploration basins, especially offshore ones, wells are rare and usually locate in the higher positions. The source rocks in basin centers are buried deeply and are not drilled. Therefore, it is the key for basin/sag evaluation to study the thermal evolution and hydrocarbon expulsion history of source rocks in basin centers. Case studies have been carried out in the Jiaojiang Sag of the East China Sea Basin. Based on the measured temperature and R_o data collected from wells locating in the sag edge or the higher positions, by means of forward modeling method, the lithosphere structure and thermal history of the Jiaojiang Sag have been recovered, and the thermal history of Paleocene source rocks in the whole sag have been modeled. The results show that the maximum R_o of Paleocene source rocks in the sag is 2.8%, indicating over-mature state. The total amount of oil expulsion is a little bit more than that of gas expulsion, and the amount of hydrocarbon expulsion is 33×10⁸ m³ oil equivalent. Hydrocarbon expulsion mainly took place before Miocene. In the future exploration, the prospects with good traps and were formed before Miocene in the central uplifts should be focused on.