The occurrence characteristics of oil in shales matrix from organic geochemical screening data and pore structure properties: An experimental study

The occurrence characteristics of shale oil are of great significance to the movability of shale oil. In this study, the occurrence characteristics of oil in the shale matrix at Funing Formation shale in Subei Basin were quantitatively evaluated by organic geochemistry and microscopic pore structure characterization experiments. The Multiple Isothermal Stages Pyrolysis (MIS) experiment results show that the content of total oil, adsorbed oil, and free oil in the shales are 3.15–11.25 mg/g, 1.41–4.95 mg/g, and 1.74–6.51 mg/g, respectively. among which the silicon-rich shale has the best oil-bearing. The relative content of free oil shows an increasing trend in pores with pore diameters greater than 3 nm. When the relative content of free oil reaches 100%, the pore size of silicon-rich shale is about 200 nm, while that of calcium-rich shale, clay-rich shale, and siliceous mixed shale is about 10 nm. The occurrence law of adsorbed oil is opposite to that of free oil, which indicates that shale oil will occur in the pores and fractures in a free state in a more extensive pore size range (> 200 nm). This study also enables us to further understand the occurrence characteristics of shale oil under the interaction of occurrence state and occurrence space.