Oil & Gas Geology ›› 2011, Vol. 32 ›› Issue (2): 175-181,228.doi: 10.11743/ogg20110203

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Characteristics and poolforming patterns of the Triassic immature oil in Wenmingzhai area, the Dongpu Depression

  

  • Online:2011-04-28 Published:2011-09-26

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 3rd 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 3rd and 4th members of Shahejie Formation in Puwei area. The poolforming pattern is that hydrocarbons generated by young source rocks accumulate in old reservoirs.