Effects of deep CO2 on petroleum and thermal alteration: The case of the Huangqiao oil and gas field

The crude oil of the Huangqiao region is light or condensate oil, with low densities of 0.7933-0.8255 g/cm3. Saturated hydrocarbons comprise 90.06%-97.37% the crude oil, while the aromatic, non-hydrocarbon and asphaltene fractions are very small. The n-alkanes range from C13 to C34, with highest abundances at C16 and C17. The gas chromatogram of the crude oil shows an unresolved hump or unresolved complex mixture (UCM) distribution of a complete n-alkane series, non-odd/even predominance, and major n-alkane peaks on the highest positions of the UCM distribution. This may indicate that deep mantle-derived CO2 fluid extracted and accumulated the oil now found in the reservoirs or source rocks.