The role of water in the laboratory thermal advancement of immature type I kerogen from the Cretaceous Qingshankou Formation in China

To understand variations in geochemistry, organic petrology, and chemical composition of crude oil and byproducts, an immature sample from the Cretaceous Qingshankou Formation in the Songliao Basin, China, was analyzed by anhydrous and hydrous pyrolysis (AHP/HP) at a wide range of temperatures ranging from 300 °C to 450 °C. The geochemical parameters: TOC, S(2), HI, and T(max) obtained from Rock–Eval pyrolysis showed both a decrease and an increase as thermal maturity progressed under HP and AHP conditions. Gas chromatography (GC) analysis showed the presence of n-alkanes in the C(14) to C(36) range in both expelled and residual byproducts, a Delta-shaped configuration although many samples had a gradually reducing (tapering) trend toward the high range. Gas chromatography-mass spectrometry (GC–MS) analysis revealed both an increase and a decrease in biomarker and very small changes in aromatic compound variations with increasing temperature during pyrolysis. To be more specific, C(29)T(s) biomarker increased with temperature for the expelled byproduct, while the opposite trend was observed for the residual one. Next, The T(s)/T(m) ratio initially increased and then decreased with temperature while the C(29)H/C(30)H ratio fluctuated for the expelled byproduct but increased for the residual. Moreover, the GI and C(30) rearranged hopane to C(30) hopane ratio remained unchanged whereas the C(23) tricyclic terpane/C(24) tetracyclic terpane ratio and the C(23)/C(24) tricyclic terpane ratio showed varying trends with maturity alike the C(19)/C(23) and C(20)/C(23) tricyclic terpane. Ultimately, based on organic petrography observations, increasing the temperature resulted in higher bitumen reflectance (%Bro, r) and optical and structural alterations in the macerals. The findings of this study provide valuable insights for future exploration endeavors in the studied region. Moreover, they contribute to our understanding of the significant role of water in the generation and expulsion of petroleum and associated byproducts, thereby facilitating the development of updated models in this field.