Coupling relationship between sandstone reservoir densification and hydrocarbon accumulation: A case from the Yanchang Formation of the Xifeng and Ansai areas, Ordos Basin

The Chang 8 member of the Xifeng Area and the Chang 6 member of the Ansai Area are taken as examples to define the relationship between the sandstone densification and accumulation from fluid inclusion identification, simulation of sandstone porosity evolution, and analysis of oil charge critical experiment. The fluid inclusion fluorescence shows that there is quartz overgrowth containing the residual asphalt and hydrocarbon inclusions existing in the sandstone reservoir of Yanchang Formation. The simulation of porosity evolution shows that the sandstone reservoir was not tight sandstone during the key accumulation period for the porosity was greater than 10%. The oil charge critical experiment indicates that the oil cannot charge into the sandstone if the porosity is less than 10% in Xifeng and Ansai, even under pressurized conditions. The results demonstrate that the Yanchang Formation of Xifeng Area and Ansai Area in the Ordos Basin is a typical “postforming” tight sandstone hydrocarbon reservoir in which the sandstone undergoes densification after oil accumulation. The compaction and cementation following the oil charging lead to the densification of sandstone.