OIL EXPLORATION POTENTIAL OF THE XINGOUZUI FORMATION IN ZIFUSI SAG

The Zifusi Sag, located in the southeast of the Jiangling Depression, has experienced three phases of tectonic evolution since the basement formed, i.e. the first phase from Late Jurassic to Eocene when Xingouzui Formation deposited, the second phase from the Eocene Jingsha Formation to the Oligocene Jinghezhen Formation, and the third phase from Neogene to Quaternary. The sag is characterized by the alternation of uplifts and depressions in a northwest direction. Source rocks are found in the Paleogene brine lake deposits of the upper Shashi Formation and lower Xingouzui Formation. The source rock II of the Lower Xingouzui Formation has the highest hydrocarbon generation potential, with the source rock I, which is mainly distributed in the center of the sag, as the second. In the Lower Xingouzui Formation, there exists a synchronous source rock-reservoir-seal system, while in the Jingsha Formation, the hydrocarbon generated in the lower part but accumulated in the upper. Crude oil from source rocks migrated through fractures and deltaic sandbodies towards the structural zones on both sides of the sag. The co-existence of autochthonous oil system in Lower Xingouzui Formation and the allochthonous oil system in the Jingsha-Qianjiang Formation formed the basic feature of oil and gas accumulation in the Zifusi Sag. Based on the above, it is predicted that the west part of the Jingzhou anticline, which is located in the north of the sag, is the most favorable target for oil exploration, and the east part of the Jingzhou anticline and the west part of the sag subordinate.