International Geologiical Congress - Oslo 2008

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BGB-02 Geomicrobiology: Low-temperature alteration, mineralization, and microbial interactions

 

Effects of sulfate reducing bacteria on molecular composition of gaseous fractions (C1-C5) in normal crude oils

 

Hakan Hosgörmez, Istanbul University (Turkey)
Esra Sungur, Istanbul University (Turkey)
Nihal Dogruöz, Istanbul University (Turkey)
Sedat Inan, TÜBİTAK Marmara Research Center (Turkey)
Seyis Cemil, TÜBİTAK Marmara Research Center (Turkey)
Aysin Cotuk, Istanbul University (Turkey)
Namik Yalcin, Istanbul University (Turkey)
 

 

It is still not well-known, whether and how hydrocarbons are utilized by sulfate reducing bacteria (SRB) under anaerobic conditions as a carbon source. Few previous studies reported that hydrocarbons are used by SRB and H2S and CO2 are formed, subsequently. However, which of the hydrocarbons fractions and molecules are preferred by these bacteria and how they are compositionally and isotopically affected by bacterial activity are not investigated in detail.

This study aims to investigate the effects of SRB on the molecular composition of hydrocarbons. For this purpose a set of samples of 50 ml crude oil inoculated by SRB in 100 ml sterile glass-vials were prepared. Another set of samples containing only crude oil without SRB were also prepared as control samples for comparison purposes. All these sets were stored under anoxic and dark conditions in shaker incubators (100 rpm) at 28oC for six months. After six months, amount and composition of head-space gases in glass-vials were determined both in samples with and without SRB.

Comparison of results showed that amounts of nC4, iC5, nC5 components decreased and that of C2, C3 and iC4 increased in SRB inoculated sample sets. In other words hydrocarbon compounds heavier than nC4 were altered and lighter than nC4 are formed by bacterial activity. Hereby, amount of newly formed propane is several times higher than the amounts of newly formed ethane and iC4.

Furthermore, molecular composition of C15+ hydrocarbons in both sample sets and amount of CH4 remained unchanged. Increase of CO2 in SRB inoculated samples is interpreted as another indicator for, that SRB use hydrocarbons. Hereby, only the C2-C5 compounds are affected. Furthermore, the isotopic composition of δ13C from methane, ethane, propane, butane and pentane both from samples with and without SRB will be investigated for their variations.

 

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