Page 178 - Primer on Enhanced Oil Recovery

168 Primer on Enhanced Oil Recovery

reactions, the presence of compounds of trace elements such as K, Na, Ca, Mg, etc.
is vitally important. Those elements and their compounds are usually present in the
reservoir connate water. It is vitally important that all this is well understood and
taken into the account when other physicochemical methods of reservoir stimulation
are used. The best outcome, highest oil extraction, are achieved when all methods,
such as injection of polymer solutions, surfactants, alkalies, mycelial solutions in
combination with bio-effects are used. Even higher results are achieved at the well
calculated and executed periodic sequential stimulation with various solutions for
the full synergistic effect.
It should be stressed again that microbiological methods of enhanced oil recov-
ery as compared with traditional physicochemical reservoir stimulation methods are
low-cost, are simple in implementation and can be applied in deposits with hard-to-
recover oil reserves. Biotechnologies not only contribute to a significant increase in
oil recovery, but also reduce the impact of water influx on operational performance.
Along with this, microbiological methods allow solving the issues of creating
waste-free technologies and improving the environmental situation of the developed
fields. This all provides solid foundation for the further MEOR development and
expansion of MEOR applications.

13.3 Implemented projects

The first commercial microbiological effects on the reservoir began in the middle
of the last century. One of the main factors ensuring the effectiveness of biotechno-
logical methods is the correctly chosen nutrient substrates and the environment for
the microorganisms. Microbiological effects on the reservoir can be divided into
methods based on the activation of aerobic processes and methods based on the
activation of anaerobic processes. However, aerobic methods simultaneously stimu-
late the development of anaerobic and vice versa. For this reason, there can be no
purely aerobic or anaerobic processes, there are processes in which this or that type
of processes prevails.
Currently, the following technologies are being developed, based on the forma-
tion of metabolic products directly in the reservoir:

a culture of microorganisms is introduced into the formation together with a nutrient
substrate;
only a nutrient substrate is introduced into the reservoir to activate the native reservoir
microflora.
The most widespread technology is “molasses fermentation”. It is based on the
introduction into the reservoir of molasses and microorganisms that can ferment
hydrocarbon substances. The result of microbial activity in this case is production
of bio-methane and CO 2 In this case the preference is given to the injection of
mixed cultures of aerobic and anaerobic microorganisms. Various materials, such
as yeast brew, whey, aerated solutions of nitrides and phosphorus salts, are nutrients