Research Article| May 01, 2007 Geochemical evidence of secondary microbial methane from very slight biodegradation of undersaturated oils in a deep hot reservoir Alexei V. Milkov; Alexei V. Milkov 1BP America, 501 Westlake Park Boulevard, Houston, Texas 77079, USA Search for other works by this author on: GSW Google Scholar Leon Dzou Leon Dzou 1BP America, 501 Westlake Park Boulevard, Houston, Texas 77079, USA Search for other works by this author on: GSW Google Scholar Geology (2007) 35 (5): 455–458. https://doi.org/10.1130/G23557A.1 Article history received: 20 Nov 2006 rev-recd: 04 Jan 2007 accepted: 09 Jan 2007 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Alexei V. Milkov, Leon Dzou; Geochemical evidence of secondary microbial methane from very slight biodegradation of undersaturated oils in a deep hot reservoir. Geology 2007;; 35 (5): 455–458. doi: https://doi.org/10.1130/G23557A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A rare finding of early mature undersaturated oils with low gas/oil ratios enables us to document secondary microbial methane generation during very slight biodegradation in a deep hot reservoir in the ultradeep-water of the Gulf of Mexico. In three studied gas samples, methane is enriched in 13C (δ13C is from -63‰ to -64‰) relative to pure thermogenic methane (estimated δ13C is from -71‰ to -67‰) and pure primary microbial methane (δ13C is -68‰). Carbon dioxide in gases has δ13C values that negatively correlate with δ13C values of pure thermogenic methane. Methane is unusually enriched in heavy isotope 2H relative to associated ethane. Some extracted oils are depleted in long-chain alkyl aromatics. These lines of geochemical evidence suggest anaerobic microbial degradation of oil and subsequent reduction of resulting carbon dioxide to methane. Although specific geobiological details of secondary microbial methane generation are unclear, this process may be partially responsible for charging some of the largest gas and gas hydrate fields in the world. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.