Abstract:

Abstract: Experimental analyses of group composition, carbon isotope and saturated hydrocarbon chromatogrammass spectrum were carried out on the crude oil and oil sand extract samples from the Triassic in Wenmingzhai area and the source rocks in the lower 3^rd member of Shahejie Formation in Puwei area, Dongpu depression. The saturated hydrocarbon content of the crude oil and oil sand extract is in the range from 39.44% to 51.01%. Their carbon isotope of group composition ranges from-28.92‰ to-26.54‰ (PDB), and the fractionation effect of the carbon isotope among aromatic hydrocarbon, nonhydrocarbon and asphaltenes is relatively insignificant. The Pr/Ph ratio is less than 0.5, indicating the predominance of Phytane. The values of sterane C₂₉ 20R/(20R+20S) and C₂₉ αββ / (ααα+αββ) are 0.29-0.34 and 0.25-0.34 respectively. The C₂₇content is slightly predominant in the sterane’s series, while the diasteranes content is extremely low. The gammacerance content is relatively high and the gammacerance to C₃₀ hopanes ratio is 0.70-0.81, indicating the geochemical characteristics of immature oil formed in a sedimentary environment with high water salinity. Oilsource correlation reveals that the immature oil in the Triassic reservoirs in Wenmingzhai area are sourced from the mudstone in the 3^rd and 4^th members of Shahejie Formation in Puwei area. The poolforming pattern is that hydrocarbons generated by young source rocks accumulate in old reservoirs.