Fluid inclusions and hydrocarbon accumulation stages of the Chang 7₃ sub-member in the Zhijing-Ansai area in the Ordos Basin

Influenced by Late Cretaceous tectonic uplift, fluid inclusion techniques were employed to determine the hydrocarbon accumulation stages of the Chang 7 3 sub-member in the Zhijing-Ansai area.There were two fluorescent oil inclusions in the Chang 7 3 sub-member.The green fluorescent oil inclusions indicated the relatively low-maturity oil, the homogenization temperatures of coeval aqueous inclusions were 83.8-89.5 ℃.The blue fluorescent oil inclusions indicated the relatively high-maturity oil, the homogenization temperatures of coeval aqueous inclusions exhibited two peaks which were 90.6-109.4℃ and 110.1-137.4℃.Combining the burial-thermal history of four wells, there were three stages of hydrocarbon accumulation.A smallscale charging of the relatively low-maturity oil occurred around 131-122 Ma.During the large-scale charging of the high-maturity oil, the hydrocarbon generation of source rock peaked (c.114 to 100 Ma).Late tectonic uplift resulted in an oil adjustment stage (88-72 Ma), corresponding to the high-maturity oil charging time.