Study on the Geochemical Genesis and Differences of Ordovician Oil and Gas Reservoirs

The study of fluid inclusions in petroliferous basins is an effective method to understand hydrocarbon migration and accumulation. In this paper, the fluid inclusions in the Ordovician carbonate rock samples taken from the TS3, TP18, YQ8 and YJ2-3 wells in Tahe Oilfield are analyzed by experiments, the purpose is to explore the accumulation period of the Ordovician oil and gas reservoirs in the Tahe area and the reasons for the differences between different blocks.The results show that the Ordovician Yingshan Formation and the Yifangfang Formation in the Tahe area are rich in fluid inclusions, and there are only a single phase of oil, gas and brine in the phase. There are also two phases of oil, gas and water mixed with each other. According to the fluorescence characteristics and homogenization temperature of hydrocarbon inclusions, combined with the burial history-thermal evolution history of the study area, it is determined that the Tahe oil and gas reservoir is filled in the fourth stage, in the middle of the Caledonian period (454-446 Ma), and in the late Hercynian-Indosinian period (255-217 Ma), late Yanshanian period(143-99 Ma), Himalayan period (25-5 Ma).Among them, the middle of Caledon is mainly filled with low-mature oil, with a small amount of mature oil; the late high-mature oil in the late Hercynian is filled with some mature oil; the late Yanshan is mainly filled with high mature oil; during the Himalayan period, as the depth of burial continues to increase, the cracking of the accumulated hydrocarbons has occurred, mainly the migration of gas hydrocarbons. The four wells selected in this study belong to different tectonic units, after analysis, the author believes that the difference between single wells is on the one hand the influence of hydrocarbon thermal evolution and the other is influenced by tectonic movement.