Artificial maturation of a Silurian hydrocarbon source rock: Effect of sample grain size and pyrolysis heating rate on oil generation and expulsion efficiency

Although artificial maturation of hydrocarbon source rocks by laboratory pyrolysis is far from representing natural maturation, it is a useful tool to investigate the process. In this study, we used routine open system pyrolysis for powder samples and Restricted System anhydrous Pyrolysis (RSP) for cm-sized Silurian shale source rock fragments to artificially mature the samples to different end-temperatures in the presence of a flowing carrier gas. Maturation experiments on rock fragments enable the simulation of physical barriers for the generated hydrocarbons that need to be overcome before expulsion from the source rock can occur. Based on the artificial maturation results in this study, oil expulsion efficiency from the Silurian shale source rock was 46% at the early oil generation stage and increased to 74% at approximately the peak oil generation stage. Furthermore, we have compared artificial maturation results from powder-form and fragment-form samples with natural-maturation series and found that artificial maturation of fragment-form samples sufficiently resembles natural maturation of the Silurian shales. It is therefore possible to simulate the early, middle and peak oil generation stages of natural maturation and expulsion efficiencies. This implies that, lab-based oil expulsion efficiencies from increasing maturity and hydrocarbon generation can be incorporated into the basin modeling. Basic analytical protocols for open-system and restricted-system pyrolysis employed to determine oil expulsion efficiency. [Display omitted] •Powder- and fragment-form Silurian shale samples were artificially matured.•Artificial maturation of fragment-form samples is more comparable to natural maturation.•Oil expulsion efficiency can be estimated at varying artificial maturation stages.•Artificial maturation-based oil expulsion efficiency estimates can be used to calibrate basin models.