Multiparameter cluster analysis of crude oil type in Shahejie Formation, southern slope of Niuzhuang sub-Sag

Multiple geochemical parameters of isoprenoid hydrocarbon, individual hydrocarbon carbon isotope, gonane and terpane in source rock extraction content components from the Niuzhuang sub-Sag were compared. Biomarkers such as phytane, gammacerane, homohopane series dinosterane and 4-methylsteranes were regarded as the fingerprint parameters of source rock features. According to clustering analyses, crude oils from the Shahejie Formation were classified into 3 genetic types as followed. The crude oils of type Ⅰ clustered with the source rocks from the 3rd member of the Shahejie Formation, and were featured by low contents of phytane, gammacerane, C₃₅ homohopane, dinosterane and 4-methyl αααC₂₉ steranes, showing the geochemical characteristics of source rocks in the lower part of the 3rd member of the Shahejie Formation which developed in weak oxidizing and low salinity environment. The crude oils of type Ⅱ clustered with the source rocks from the 4th member of the Shahejie Formation, and were featured by high contents of phytane, gammacerane, C₃₅ homohopane, dinosterane and 4-methyl αααC₂₉ steranes, showing the geochemical characteristics of source rocks in the upper part of the 4th member of the Shahejie Formation which developed in strong reducing and high salinity environment. The crude oils of type Ⅲ had no significant clustering relationship with the source rocks from the 3rd and 4th members of the Shahejie Formation, but the average value of main clustering parameters was in the range of the above-mentioned source rocks, indicating that the crude oils of type Ⅲ might be the mixture of type Ⅰ and Ⅱ.