Steroselective biodegradation of hopane epimers to 25-norhopanes in petroleum

Conference · Tue Oct 01 04:00:00 EDT 1996

OSTI ID:370434

Peters, K E ^[1]; Moldowan, J M; Fago, F J ^[2]

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1. Mobil Exploration & Producing Technical Center, Dallas, TX (United States)
2. Stanford Univ., CA (United States); and others

In-reservoir microbial removal of the C-25 methyl group from the C{sub 31} to C{sub 35} 17{alpha}21{beta}(H)-hopanes generates 25-norhopanes in West Siberian and Californian crude oils. Higher hopane homologs are progressively more resistant to this demethylation. The 22R epimers of the C{sub 34} and C{sub 35} hopanes are preferentially degraded compared to 22S, while the opposite applies to the C{sub 31} and C{sub 32} hopanes. Molecular mechanics calculations show that the size and conformation of the side chain at C-21 control the susceptibility of the C-25 methyl to biodegradation. The conversion of each hopane to its corresponding 25-norhopane occurred without significant side products and was incomplete at the time of sampling. This is indicated by the match between reconstructed C{sub 31} to C{sub 35} hopane distributions for heavily biodegraded oils (hopane parent plus 25-norhopane product for each homolog) and those of related, nonbiodegraded oils. The 25-norhopane/hopane ratio improves our ability to distinguish levels of biodegradation among heavily degraded oils.

• OSTI ID: 370434
• Report Number(s): CONF-960376--
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
55 BIOLOGY AND MEDICINE
BASIC STUDIES
BIODEGRADATION
CHEMICAL COMPOSITION
MOLECULAR STRUCTURE
PETROLEUM