Demethylated hopanes in crude oils and their applications in petroleum geochemistry |
| |
| Authors: | John K Volkman Robert Alexander Robert Ian Kagi Garry Wayne Woodhouse |
| |
| Institution: | Petroleum Geochemistry Group, School of Applied Chemistry, Western Australian Institute of Technology, South Bentley, Western Australia, 6102, Australia |
| |
| Abstract: | Analyses of some Australian crude oils show that many contain varying concentrations of A/ B-ring demethylated hopanes. These range from C26 to C34 and have been identified from their retention times and mass spectral data as 17α(H)-25-norhopanes. Comparison of hopane and demethylated hopane concentrations and distributions in source-related, biodegraded oils suggests that demethylated hopanes are biotransformation products of the hopanes. Further, it appears that the process occurs at a late stage of biodegradation, after partial degradation of steranes has occurred. Demethylated hopanes are proposed as biomarkers for this stage of severe biodegradation. The presence of these compounds in apparently undegraded crude oils is thought to be due to the presence of biodegraded crude oil residues which have been dissolved by the undegraded crude oil during accumulation in the reservoir sands. The timing of hopane demethylation, relative to the degradation of other compounds, has been assessed and the progressive changes in crude oil composition with increasing extent of biodegradation have been identified. The use of demethylated hopanes as maturity parameters for severely biodegraded crude oils, and the applicability of established biomarker maturity parameters to such oils, are also discussed. |
| |
| Keywords: | Author to whom correspondence should be addressed |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
