25th International Meeting on Organic Geochemistry IMOG 2011

P-015
Can comprehensive analysis of degraded oil indicate the
conditions under which biodegradation occurred in an oil
reservoir?
Thomas Oldenburg 1 , Steve Larter 1,2 , Melisa Brown 1 , Ben Hsieh 1 , Ian Head 2 , Martin
Jones 2 , Caroline Aitkins 2 , Neil Gray 2
1 University of Calgary, Calgary, Canada, 2 Newcastle University, Newcastle upon Tyne, United Kingdom
(corresponding author:toldenbu@ucalgary.ca)
Most of the world petroleum reserves are
biodegraded with the largest oil reserves being found
on the flanks of foreland basins in Canada and
Venezuela. A significant fraction of the conventional
oil reserves are also biodegraded and major future oil
discoveries are likely to be mainly biodegraded, too
as they are expected in deep-water areas with low
thermal gradients and shallow exploration targets.
These petroleum reservoirs are cooler than 80ºC and
therefore ideal environments for microbial
degradation. As it became accepted only recently that
biodegradation of petroleum in reservoirs proceeds
anaerobically little is known about the processes and
the controlling factors involved in subsurface
hydrocarbon and non-hydrocarbon degradation.
A laboratory microcosm study of anaerobic
petroleum degradation under sulphate-reducing and
methanogenic conditions was undertaken over a
period of two years. The microbial communities and
hydrocarbon distribution patterns were analysed
parallel to the detailed analysis of the distribution of
polar compounds using an ultra-high resolution 12T
Fourier Transform Ion Cyclotron Resonance Mass
Spectrometer (FTICRMS). The whole degraded oil
samples were analysed for acidic components (using
electrospray ionisation (ESI) in negative mode), basic
compounds (ESI positive mode) as well as for low
A
original 302 days metha. 686 days metha.
polar and highly aromatic components such as
sulphur and aromatic hydrocarbon compounds using
Atmospheric Pressure Photoionisation (APPI)
techniques.
The forming or destruction of some polar compound
classes indicates the conditions under which oil
B
biodegradation occurs. Whereas many hydroxy and
carboxylic acid compounds are formed (Fig 1A-C) the
occurrence of e.g. some NOx classes are related to
biodegradation mechanism. This novel knowledge
received from laboratory experiments will be used to
predict the biodegradation history of natural
biodegraded oil reservoirs.
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