The microbial ecology of 45 high temperature (> 50 ° C) petroleum reservoirs was
investigated by isolating and characterizing bacteria that were present in their produced
fluids. Initial work was aimed at selecting a suitable high temperature petroleum
reservoir for the study of natural microbial populations. Experimental work then
focussed on establishing the physico-chemical conditions that prevail in the selected
reservoir and on developing media and enrichment conditions for the isolation of
microorganisms indigenous to the reservoir. The ability of reservoir bacteria to grow
and survive under the physical and chemical conditions found in the selected reservoir
was used to assess the likelihood of an indigenous origin for these bacteria.
The petroleum reservoir selected for study was the Alton petroleum reservoir (SW
Queensland, Australia). It was established that most of the physico-chemical conditions
in the Alton reservoir had remained unchanged since oil recovery began. The stability
of redox conditions (90 mV) in the reservoir over its operating life was identified as an
important factor in the coexistence of strict aerobic and strict anaerobic bacterial
populations within the reservoir. An important change that has occurred in the Alton
reservoir over its operating life because of oil recovery was an increase in water pH
from 6.41 to 8.42 as a result of carbon dioxide loss (1.36 atm to 0.0134 atm) from the
reservoir.
Development of novel enrichment procedures that simulated Alton reservoir conditions
led to the isolation of previously unreported aerobic and anaerobic populations of
thermophilic bacteria. The aerobic bacteria isolated were identified as either endosporeforming
heterotrophic bacteria from the genus Bacillus or nonspore-forming
heterotrophic bacteria resembling members of the genus Thermoleophilum. All aerobes
grew on carbon sources such as acetate and n-heptadecane that are normal constituents
of the reservoir. The anaerobic bacteria isolated were characterized as sheathed
fermentative bacteria from the order Thermotogales or non-sheathed fermentative
bacteria. In parallel studies, the natural microbial populations in other reservoirs were
investigated and I concluded that fermentative microorganisms were common
inhabitants of high temperature petroleum reservoirs. The isolation of fermentative
bacteria from these high temperature petroleum reservoirs established that fermentative
bacteria are a fourth major microbial group, together with hydrocarbon-oxidizers,
sulphate-reducers and methanogens, to be reported in petroleum reservoirs. The
fermentative bacteria use organic nutrients and carbohydrates, but not contemporary
crude oil as the principal nutrient source within reservoir waters.
The thermophilic bacteria isolated from Alton petroleum reservoir demonstrated growth
characteristics such as temperature (optima 50-70 ° C and range 37-85 ° C), pH (optima
6.0-9.0 and range 5.0-9.0 and salinity (optima 0-15 g per litre and range 0-30 g per
litre), that were consistent with conditions encountered in the Alton reservoir
(temperature 75 � C, pH 8.5 and TDS 2.7 g per litre). The isolated bacteria also
demonstrated a number of characteristics that might enable them to survive adverse
conditions that could be encountered in a petroleum reservoir environment. The
characteristics that contribute to aerobic bacteria surviving in and overcoming periods
of oxygen limitation include well-documented processes such as sporulation, by
Bacillus spp., and microaerophily. The characteristics that contribute to fermentative
bacteria surviving were: (1) a natural tolerance to reservoir physico-chemical
fluctuations, (2) an ability to remain viable when metabolic activity was suppressed to
very low rates by the growth-limiting conditions imposed, and (3) possible formation of
viable ultramicrobacteria (UMB). Formation of UMB (bacteria smaller than 0.3 |im) by
thermophilic bacteria has not been reported previously.
The recovery of thermophilic UMB by filtration from the Alton reservoir water
indicates that these bacteria occur in natural habitats. This study found the formation of
thermophilic UMB and their survival characteristics differed considerably from that
reported for the mesophilic, marine bacterium Vibrio sp. DWI. Unlike mesophilic
marine bacteria, thermophilic bacteria did not always respond to nutrient deprivation by
forming UMB and that these UMB did not show any increased ability to survive in the
face of adverse conditions. Although the formation of UMB as part of routine cell
growth and division was not demonstrated directly in this study, circumstantial
evidence suggests that they form part of a natural life cycle. The exact conditions that
result in UMB formation and their role in survival remain unresolved.
The capacity of nonspore-forming indigenous populations from Alton to survive sudden
shifts in environmental conditions that might result from common oilfield operations
was poor. Such operations were demonstrated to be inhibitory or lethal to Alton
reservoir bacteria. It also was concluded that such oilfield operations suppress
indigenous microbiota. However, the impacts of most oilfield operations within a
reservoir are likely to be confined to the immediate area surrounding injection and
producing wells. Minimizing the localized effects of oilfield practices on indigenous
reservoir populations will lead to the better management of undesirable microbial
activity in reservoirs such as H2S formation (souring) and facilitate development of
better microbially mediated oil recovery process. This study showed that selected
reservoir isolates possess characteristics which are suitable for in situ biotechnological
applications such as microbially enhanced oil recovery (MEOR). Characteristics
favourable for enhanced oil recovery include a capability for UMB formation, which
would enable better dispersion, and resistance to high concentrations of reservoir
components such as calcium, magnesium, strontium, heavy metals and hydrocarbons.
| Identifer | oai:union.ndltd.org:ADTP/218965 |
| Date | January 1995 |
| Creators | Grassia, Gino Sebastian, n/a |
| Publisher | University of Canberra. Applied Science |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Gino Sebastian Grassia |
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