A Novel Approach for Investigating the Paleo-Oil Filling Orientations: Constraints by Biodegradation Evaluation Proxies and Recovered Biomarker Parameters

• Published in: Energy & fuels Vol. 38; no. 7; pp. 5751 - 5765
• Main Authors: Shi, Bingbing, Chang, Xiangchun, Liu, Tianjiao, Zhang, Guanlong, Zhang, Pengfei, Xu, Youde, Chen, Guo
• Format: Journal Article
• Language: English
• Published: American Chemical Society 04.04.2024
• Subjects: Traditional Fossil Fuels
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.4c00231

The spatial arrangement of methyl groups in biomarkers significantly impacts their polarity and thermal stability, both of which are crucial for the chromatographic effects involved in tracing the direction of oil migration. However, biodegradation can also selectively alter the isomers of these biomarkers based on the positions of their methyl groups, making it challenging to interpret migration directions in biodegraded oils using conventional tracers. Hence, it is imperative to explore novel indicators, such as the biodegradation evaluation parameter, in order to discern the directions of oil migration. However, conventional proxies for evaluating biodegradation, such as C29 25-nor-hopane/C30Hopane (25-NH/H), C2217-nor-tricyclic terpane/C23 tricyclic terpane (17-NT/TT), and the widely used modular analysis and numerical classification of oils (Manco) scale, often have limited applicability and resolution within a narrow range of biodegradation, particularly in long-distance migration scenarios. To address this issue and improve resolution across a broader spectrum of biodegraded oils, we developed a refined approach. This approach uses five homologues, each displaying different levels of resistance to biodegradation, to cover the complete range of biodegradation. Our novel approach provides significantly improved resolution compared to the conventional Manco scale, and our goal is to employ the contour plots generated by this approach to accurately determine the migration direction. To verify the accuracy of our results, we conducted validation experiments using conventional tracers. Our validation experiments included measurements of isomer ratios of pyrrolic and thiophene ring compounds, as well as typical biomarker tracers recovered from the biogenetic information derived from biodegraded oils, specifically (C23TT+C2217-NT)/(C30H+C29 25-NH). Furthermore, we examined structural morphology, density and viscosity, the quantitative grain fluorescence index, the hydrocarbon migration effective pathway index (Hmle), and pore-permeability characteristics for further validation purposes. This refined scale for evaluating biodegradation provides comprehensive insights into biodegraded oils and serves as an essential tool for understanding patterns of hydrocarbon preferential migration and identifying promising exploration targets for biodegraded oils in both the studied regions and elsewhere.