Page 424 - Fundamentals of Enhanced Oil and Gas Recovery

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10.6 MICROBE SELECTION FOR MEOR

For a successful MEOR, it is mandatory to choose the right candidate of micro-
organisms to fulfill the desired objective by adequately production of target biopro-
ducts. Biochemical production by different microorganisms will be debated in details
in sections 10.1 to 10.5. Acquiring a thorough knowledge about the physicochemical
condition of the reservoir is of great importance in choosing the right microorgan-
isms. The right candidate not only should be capable to adapt itself to the reservoir
condition, but also should produce the desired bioproducts in adequate volumes.
Majority of the successful MEOR field trials have used anaerobic bacteria [23]. Lazar
et al. [108] mentioned four different sources suitable to isolate microorganisms benefi-
cial for MEOR processes:
1. Formation waters;
2. Sediments from formation water purification plants;
3. Sludge from biogas operations; and
4. Effluents from sugars.
Both pure and mixed cultures have been used in field trials. Youssef et al. [6] men-
tioned the improvement in the technology of MEOR as using mixture cultures adapted
to the nutrients and reservoir condition such as temperature and pressure and also incor-
porating larger volumes of nutrients [105 108,110,111,113,114].Adetunji [84] specified
that mixed cultures have exhibited higher efficiency in enhancing oil recovery. There
have been several different microorganisms used in field trials. Some of them are listed in
the following:
1. Bacillus. This bacterium commonly produces biosurfactants, bioalcohols, and bio-
gases [395,396].
2. Clostridium. This bacterium commonly produces bioacids and biogases. The pro-
cess of methane production is referred to as methanogenesis [25,395,396]. This
bacterium has been proved to be effective in both sandstone and carbonate reser-
voirs [25,395,397]. For the carbonate reservoirs, matrix acidizing to improve the
permeability as well as gas generation for displacing oil have been successful
mechanisms incorporating this bacterium. For the sandstone reservoirs, clostridium
utilization has been successful to lower the oil viscosity.
3. Pseudomonas. This bacterium produces biosurfactants and biopolymers and is effec-
tive in permeability profile modification [396].
4. SRB: These bacteria result in biodegradation of oil large molecules to reduce the
oil viscosity. In addition, they produce methane through methanogenesis [25].
Among the mentioned microorganisms, Bacillus and more frequently Clostridium
are the most common ones. These microorganisms have exhibited higher percentage
of success in field trials [24].