Hydrocarbon enrichment varies dramatically in such structural belts as Xie Fengqiao

Fu Xingchang

and Caixue in the southwestern margin of Jianghan basin.The extent of hydrocarbon enrichment is found to be related to the uplift and erosion processes in the Late Eogene and the potentiality of secondary hydrocarbon generation.Evidences

such as the late mature of source rocks

crude with the same source but different maturities

and the fluid-inclusion anaysis

all suggest a possibility of secondary hydrocarbon generation in the study area.The oil reservoirs that were formed before the rise of basin were partly or entirely destroyed with the rise of the basin

structures that could capture the secondary hydrocarbon generation have relatively high hydrocarbon enrichment.Xie Fengqiao structure had captured and preserved the primary and secondary hydrocarbons

thus its enrichment level is the highest.Caixue and Fu Xingchang belts suffered from great loss of their primary hydrocarbons in the process of rise of the basin.However

Caixue belt has a higher enrichment of hydrocarbons for having received a supply of second hydrocarbon generation

while Fu Xingchang

without the process of secondary hydrocarbon generation

has a lower oil saturation and poor enrichment of hydrocarbons.