Genetic types and distribution characteristics of crude oils from Shahejie Formation in Bonan Subsag, Zhanhua Sag, Jiyang Depression

According to the characteristics of saturated hydrocarbon chromatography, GS/MS and biomarker index, combined with the geochemical features of crude oil, the hydrocarbon genetic types and distribution laws of the Bonan Subsag in the Zhanhua Sag have been analyzed based on the comparison of geochemical features of source rocks from different layers of the Shahejie Formation. The research shows that there are 2 suits of hydrocarbon source rocks in the Bonan Subsag, the 3rd member and the 4th member of the Shahejie Formation. The source rocks in the 4th member of the Shahejie Formation can be further divided into evaporate and sub-evaporate ones. All of the source rocks are obviously different in gammacerane content, Pr/Ph ratio and maturity parameters. Oil source correlation indicates that there are 5 types of oil and they have certain laws in distribution. The crude oils of types Ⅰ and Ⅱ in the 3rd member of the Shahejie Formation both originate from the source rocks in the 3rd member of the Shahejie Formation; however, they are obviously different in maturity and distribution. The crude oils of type Ⅰ in the 3rd member of the Shahejie Formation locate in the middle and upper sections of the 3rd member of the Shahejie Formation in the depression, with relatively lower maturity. The crude oils of type Ⅱ in the 3rd member of the Shahejie Formation locate in deeper formations, with relatively higher maturity. The crude oils of type Ⅰ in the 4th member of the Shahejie Formation distribute sporadically, and originate from the evaporate source rocks in the 4th member of the Shahejie Formation. The crude oils of type Ⅱ in the 4th member of the Shahejie Formation come from the sub-evaporate source rocks in the 4th member of the Shahejie Formation, and are mainly self-generated and self-reserved. Mixed oil and gas come from source rocks in both of the 3rd and 4th members, and locate far away from source center influenced by faults, mainly in step-fault zones.