Growth of sulfate reducing bacteria (SRB) in crude oil, with variable amounts of enrichment
medium was studied. Gullfaks, Snorre and Grane crude oil were used as carbon and
energy source. In Gullfaks crude oil anaerobic cultures with 2 to 95 % v/v brine were
inoculated with a mixed culture of SRB and incubated at 30 C for 4 weeks. The cultures
were amended with volatile fatty acids (VFA) to enhance growth of SRB. Cultures were
analyzed for growth of SRB and H2S production. Growth of SRB was observed in cultures
with 6 % water and more, and H2S production was observed in cultures with 10 % water
and more. In cultures without VFA H2S production was not observed. In Snorre and Grane
crude oil anaerobic cultures with 2 to 10 % v/v enrichment medium were inoculated with a
mixed culture of SRB and incubated at 30 C for 4 weeks. Half of the cultures were
amended with VFA to enhance growth of SRB; the other half contained only crude oil as
carbon and energy source. In cultures grown on crude oil from Snorre, with or without VFA,
no growth of SRB or sulfide production was observed. In contrast, growth of SRB and H2S
production was observed in all cultures with crude oil from Grane, regardless the water
amount and whether acids were added or not. Chemical analysis of the crude oil showed
major differences in oil composition with regards to the lighter oil components. Snorre oil
contained 23 % Wt of oil compounds lighter than C10, while Gullfaks and Grane oil
contained 9.7 and 2.9 % Wt respectively. The light oil fraction also contains the most water
soluble components, including benzene and toluene known to be toxic to many bacteria,
including SRB. Since a typical export specification for crude oil is less than 0.5 % water, the
results from Gullfaks and Snorre (light crude oil) showed that growth of SRB in transport
pipelines was strongly inhibited under these conditions. In cultures with crude oil from
Grane, a heavier crude oil, growth of SRB was observed even at 2 % water content.
Keywords: Crude oil, Gullfaks, Snorre, Grane, water content, anaerobic growth, SRB, H2S,
chemical oil analysis