A comparative study on the geochemical characteristics of expelled and retained oil from hydrocarbon generation simulation of Australian Tasmanian oil shale Ⅰ: fraction and isotopic compositions

Abstract

Australian Lower Permian Tasmanian oil shale is rich in organic matter with relatively lower maturity, and the bio-precursor of organic matter is dominated by Tasmanite. Thus it is an ideal sample for thermal simulation experiment. In order to study the compositional characteristics and thermal evolution characteristics of expelled and retained oil, artificial simulation experiments were carried out. Results show that the peak temperature for oil generation of Tasmanian oil shale is ~340 ℃. Taking the peak temperature of 340 ℃ as a boundary, the relative content of oil fractions at each temperature showed that, the content of saturated hydrocarbon and aromatic hydrocarbon decreased with the increase of temperature before 340 ℃, but increased with the increase of temperature after the peak point. The content of polar fraction and asphaltene is opposite to that of saturated aromatic fractions. The content of saturated hydrocarbon in expelled oil is higher than that in retained oil, and the content of aromatic hydrocarbon in retained oil is obviously higher than that in expelled oil. Stable carbon isotopes of the fractions of both expelled oil and retained oil have been reversed. Aromatics appeared to have the heaviest isotope, followed by saturated hydrocarbons and non-hydrocarbons. Asphaltenes generally have the lightest isotopic values. In the whole simulation process, the carbon isotope composition of retained oil is heavier than that of expelled oil, and the aromatic carbon isotope is the most stable, indicating that it is an effective indicator of oil source comparison. If the residual hydrocarbon shale in autoclave is taken as a shale oil system after hydrocarbon generation simulation, the oil saturation index (OSI) value of the shale samples in the autoclave after thermal simulation is the highest near the peak of oil generation, suggesting that maturity is one of the important factors affecting the exploration of shale oil.

Keywords

• simulation of hydrocarbon generation and expulsion
• expelled oil
• retained oil
• group component
• carbon isotope
• tasmanian oil shale
• australia