HYDROCARBON VERTICAL MICRO-MIGRATION AND ITS GEOCHEMICAL EFFECTS IN SICHUAN BASIN

According to the characteristics of the hydrocarbons in the well profiles,the hydrocarbon vertical micro-migrating tracks can be revealed and then proceed to trace to the source of hydrocarbon anomalies near surface.This is an important method of studying the near-surface hydrocarbon anomaly patterns and forming mechanism.In the oil and gas wells in Sichuan Basin,the percentage of naphthenic hydrocarbon gradually decreased while the normal alkane and isoalkane increased from deep to surface.Moreover,the ultraviolet derivative values of 280 nm and 210 nm decreased.These clearly indicate the direction of hydrocarbon vertical migration and show that the surface hydrocarbon anomalies have relation with deep reservoir.In a gas well in west Sichuan area,the hydrocarbon chromatogram of C₁—C₅ and the 3D fluorescence chromatogram of the near-surface sample are similar to that of the reservoir sample,showing the both ha-ving the same source.