Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/5314
AuthorsEtiope, G.* 
Feyzullayev, A.* 
Milkov, A. V.* 
Waseda, A.* 
Mizobe, K.* 
Sun, C. H.* 
TitleEvidence of subsurface anaerobic biodegradation of hydrocarbons and potential secondary methanogenesis in terrestrial mud volcanoes
Issue DateNov-2009
Series/Report no.9/26 (2009)
DOI10.1016/j.marpetgeo.2008.12.002
URIhttp://hdl.handle.net/2122/5314
KeywordsMud volcanoes
Methane
Secondary methanogenesis
Anaerobic biodegradation
Isotopically enriched CO2
Subject Classification03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases 
AbstractThe assessment of gas origin in mud volcanoes and related petroleum systems must consider postgenetic processes which may alter the original molecular and isotopic composition of reservoir gas. Beyond eventual molecular and isotopic fractionation due to gas migration and microbial oxidation, investigated in previous studies, we now demonstrate that mud volcanoes can show signals of anaerobic biodegradation of natural gas and oil in the subsurface. A large set of gas geochemical data from more than 150 terrestrial mud volcanoes worldwide has been examined. Due to the very low amount of C2+ in mud volcanoes, isotopic ratios of ethane, propane and butane (generally the best tracers of anaerobic biodegradation) are only available in a few cases. However, it is observed that 13C-enriched propane is always associated with positive б13 CCO2 values, which are known indicators of secondary methanogenesis following anaerobic biodegradation of petroleum. Data from carbon isotopic ratio of CO2 are available for 134 onshore mud volcanoes from 9 countries (Azerbaijan, Georgia, Ukraine, Russia, Turkmenistan, Trinidad, Italy, Japan and Taiwan). Exactly 50% of mud volcanoes, all releasing thermogenic or mixed methane, show at least one sample with б13 CCO2>+5‰ (PDB). Thermogenic CH4 associated with positive carbon isotopic ratio of CO2 generally maintains its б13C-enriched signature, which is therefore not perturbed by the lighter secondary microbial gas. There is, however, high variability in the б13 CCO2 values within the same mud volcanoes, so that positive б13 CCO2 values can be found in some vents and not in others, or not continuously in the same vent. This can be due to high sensitivity of б13 CCO2 to gas–water–rock interactions or to the presence of differently biodegraded seepage systems in the same mud volcano. However, finding a positive б13 CCO2 value should be considered highly indicative of anaerobic biodegradation and further analyses should be made, especially if mud volcanoes are to be used as pathfinders of the conditions indicative of subsurface hydrocarbon accumulations in unexplored areas.
Appears in Collections:Papers Published / Papers in press

Files in This Item:
File Description SizeFormat 
Etiope-Feyzullayev-etal-MPG-evidence-biodegradation.pdfmain article935.57 kBAdobe PDFView/Open
Show full item record

Page view(s)

92
Last Week
0
Last month
checked on Jun 22, 2017

Download(s)

23
checked on Jun 22, 2017

Google ScholarTM

Check

Altmetric