Oil-source correlation study of the Paleogene red beds in the Boxing sag of the Dongying depression, eastern China
We present a correlation study of the oil occurrence in the Paleogene red beds of the Boxing sag of the Dongying depression, eastern China. The reservoir includes the lower 4th Member of the Shahejie Formation (Es4 l) and 1st Member of the Kongdian Formation (Ek1). Sixteen source rock samples and 17 oil sand samples from the Boxing sag were collected and the biomarkers were analyzed to perform oil-source correlation. The results show that three oil types characterize the petroleum stored in the Paleogene red beds of the Boxing sag. The oil in Es4 l is classified as Type A oil and is derived from the Es3 l (lower 3rd Member of the Shahejie Formation) source rock, which was deposited in a freshwater-brackish lacustrine environment. The oil in Ek1 of the eastern sag (well Bo-8) is originated from the Es4 u (upper 4th Member of the Shahejie Formation) source rock, characterized by saline-hypersaline lacustrine environment, and classified as Type B oil. The oil within Ek1 is a mixture of oil generated from both Es3 l and Es4 u source rocks and classified as Type C oil. The distribution of the different oil types in the Paleogene red beds in the Boxing sag is controlled by faults that connect the source rocks with the reservoir bed, which are here named “oil-source faults”. The Paleogene red beds in the footwall blocks of these “oil-source faults” are the most promising oil and gas exploration target.