Hydrocarbon origin and reservoir forming model of Wuyunting structure in Xihu Depression, East China Sea Basin

In recent years, the oil and gas exploration of the Wuyunting structure in the Pinghu slope belt of Xihu Depression of the East China Sea Basin has reported good commercial discoveries, but the fluid properties of wells A and B that have been drilled are quite different. Well A is a gas reservoir and well B is a reservoir. The hydrocarbon source, filling period and accumulation model of Wuyunting structure were analyzed by biomarker compound comparison, carbon isotope analysis and fluid inclusion analysis. It is believed that the Wuyunting structural oil is a normal mature crude oil, mainly derived from the local Ningbo 19 sub-sag, Pinghu Formation coal-series source rock. The upper part of Pinghu Formation is high-mature natural gas, mainly from the main source of the eastern main shoal of Ningbo 19 sub-sag, Pinghu Formation, and the middle section of Pinghu Formation. It is a normal mature natural gas, mainly derived from local source rocks. The fluorescence of the inclusions is light yellow oil and gas inclusions and colorless gas inclusions. The uniform temperature indicates that the Wuyunting structure mainly undergoes two phases of hydrocarbon charging, 2 Ma and nowadays. The Wuyunting structure is rich in oil and gas resources, and the accumulation process is complex. Based on the hydrocarbon supply mode and the transport system, it is divided into two accumulation models: "dual-source lateral late secondary type" and "single-source vertical transport late native type".