The Lower Cambrian Qiongzhusi shale and the Upper Ordovician-Lower Silurian Wufeng-Longmaxi shale are major source rocks and important shale gas exploration targets in the Sichuan Basin. Cutting and core samples from two shale gas wells in south-western Sichuan Basin have been selected for organic matter (OM) reflectance measurement and Raman spectra analysis with the aim to determine maturity. The results were incorporated for basin modelling to construct the thermal evolution of this area. Graptolite fragments and pyrobitumens are the dominant form of OM in
Lipid biomarkers play an important role in defining oil-source rock correlations. A fundamental assumption is that composition (or ratios) of biomarkers in oil is not significantly different from that in bitumen in the source rock. In order to compare the geochemical characteristics of expelled oil and residual oil, a Permian Tasmanite oil shale was used for an artificial maturation experiment to simulate the oil generation period. The results show that the Tasmanite oil shale generated high amounts of hydrocarbons (731 mg HC/g TOC) at low maturation temperatures (340 °C). The hydrocarbon (HC) group compositions are different between the expelled oil (with more aromatic HC and saturated HC) and the residual oil (with more resin fraction and asphaltene). The Pr/Ph ratio (up to 4.01) of the expelled hydrocarbons was much higher than that in residual oil (<1.0). Maturity-related biomarkers Ts/(Ts + Tm), and αααC29-20S/(20S + 20R) and C29-αββ/(ααα + αββ), also showed complicated variations with pyrolysis temperature, especially at post peak oil generation. C27-, C28-, and C29- sterane distributions showed variations with pyrolysis temperature. Therefore, without considering the influence of maturity on the abundance of compounds, either source, maturity and/or organic matter type from the chemical characteristics may not be correct.
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