The geochemical characteristics of the Paleogene lacustrine source rock and Cenozoic oil in the eastern Huanghekou Sag, Bohai Bay Basin, China: An oil–source rock correlation

Abstract

Oil source correlations were conducted through bulk carbon isotope composition, source-related biomarkers, and maturity-related parameters to characterize the differences between two Paleogene lacustrine source rocks the Shahejie third (Es3) and fourth (Es4) members, utilizing seven Cenozoic crude oils. Es3 is dominated by type II1 sapropel kerogen, and Es4 is dominated by type II2 humic kerogen. The Es4 source rock has high gammacerane content, low Pr/Ph, high C30 steranes, high dinosteranes, and low β-/γ- and α-/γ-methyltrimethyltridecylchroman (MTTC), indicating a transgression in a saline lake during sedimentation. The low abundance of short-chain n-alkanes, high carbon peak number, abundant perylene, cadalene, and retene indicate that the Es4 input included significant amounts of ferns and gymnosperms. In contrast, the Es3 source rock was deposited in a moderately deep freshwater lake and had relatively more angiosperm and algal input with high oleanane to C30 hopane and high 1,2,7-/1,2,6- trimethylnaphthalene (TMN) ratios. The oils have relatively high sulfur content except oil O1. The larger population of oils were derived from the Es4 system, and were mixed with the low sulfur oil produced by Es3. The oil maturity parameters are generally higher than those seen in the two source where sampled, indicating that the oils were generated from source kitchens of higher thermal maturity in the east and south. The results of this study will contribute to the understanding of the evolution of Paleogene sedimentary environments and regional oil and gas exploration.