The Coupling Relationship between Diagenetic Fluid Evolution and Hydrocarbon Accumulation in the Ordovician of Yubei Area, Tarim Basin

Although the method of homogenization temperature (Th) of fluid inclusion projecting on burial history diagram with thermal curve to obtain hydrocarbon charging times has been widely and effectively used,some uncertainty arises on the multi-cycle superimposed basins,in which one Th can appear at two or more than two depths. For the purpose of reducing the multiple solutions,63 samples of the Ordovician in Yubei area have been employed to make diagenetic observation,carbon and oxygen isotope analyses,and fluid inclusions analyses. Diagenetic sequence and two parameters of Th and trapping pressure (P_t) have been utilized to doubly constrain the times of hydrocarbon charging. When the Th of oil inclusion and its coeval aqueous inclusion,gas to liquid ratio of oil inclusion and chemical components of oil inclusion are obtained,the trapping pressure of the oil inclusion can be thermodynamically modeled by the software PVTsim. After the P_t of oil inclusion and the Th of its coeval aqueous inclusion were projected doubly on burial history diagram for each well,the hydrocarbon charging time would be determined. Then,we put all the charging times on the same geological age axis,three events of hydrocarbon charging occurred in the Ordovician of Yubei area,Tarim basin:the first event took place from 447.1 Ma to 444.0 Ma (during the Late Caledonian); the secondary event from 295.0 Ma to 274.7 Ma (during the Late Hercynian); the tertiary event from 14.7 Ma to 8.8 Ma (during the Late Himalaya). The oil pools charged by the first and the secondary event were destroyed or adjusted in the process of tectonic movement,and the oil pools charged by the tertiary event maybe the favorable exploration target.