OIL AND GAS MIGRATION PERIODS AND ACCUMULATION PROCESS IN CENTRAL ANTICLINAL ZONE IN THE XIHU SAG, THE EAST CHINA SEA BASIN

By means of inclusion thermometry and authigenic illite dating data,the oil and gas migration and accumulation model in the central anticlinal zone in the Xihu Sag of the East China Sea Basin has been studied.Fluid inclusions in reservoirs in the central anticlinal zone can be divided into salt water inclusion and organic inclusion.Homogenization temperatures of inclusions can be devided into three periods and their accordingly geologic periods are Middle Miocene,Later Miocene and Pliocene to Quaternary respectively.Isotope ages of authigenic illite in reservoir are 23.5～26.5 Ma,18.31～21.86 Ma and 12.58～13.63 Ma from north to south.This shows that the time of oil and gas accumulation in the northern part is earlier than ones in the middle and southern parts.The research result shows that there are three phases of oil and gas accumulation in the central anticlinal zone and the late-accumulation phase is the most important.Multiple phases of hydrocarbon generation,multiple recharging,multiple accumulation and multiple source rocks are fundamental oil and gas accumulation models in the zone.