Combination of basin modelling and carbazoles to investigate secondary oil migration pathways in the Dongying depression of the Bohai Bay Basin, China

This study investigates pathways of secondary oil migration, which lead to oil accumulations in the Dongying Depression with both geochemistry and basin modelling techniques. Modelling of oil migration pathways was conducted for the third and fourth members (Es3 and Es4) of the Shahejie Formation, including reconstructions of thermal maturation and hydrocarbon generation processes, which were supported by parameters of carbazoles and further reinforced by distributions of oil wells and fields. The lower interval of the Es3 source rock was deposited under a sub-oxic, freshwater environment, while the upper interval of Es4 source rock was deposited under an anoxic, hypersaline environment. The investigated 38 oil samples are classified into three groups based on oil-source correlation in the Dongying Depression as the Es3-derived oils, the Es4-derived oils, and mixed oils of Es3 and Es4 in their origin. The influence of maturity variations and source facies on carbazole parameters of the non-biodegraded oils can be ignored. Carbazole parameters can be used to trace migration distances of oil for each group of oil. Eight migration pathways are determined based on the analysis of carbazole parameters. Oil migration pathways inferred from basin modelling are consistent with those determined by carbazoles. Our results suggest two favourable oil accumulation areas along the migration pathways in the Es4 member of the Dongying Depression. •Classify the crude oils and carry out oil to source correlation in the Dongying Depression.•Determine oil migration pathways in the third and fourth member of the Shahejie Formation.•Trace secondary oil migration pathways by carbazoles.•Predict two favourable oil accumulation areas in the fourth member of the Shahejie Formation.