Page 177 - Primer on Enhanced Oil Recovery

Microbial enhanced oil recovery (MEOR) 167

suppresses the development of microbiological activity and processes. The overall
salinity of water in the reservoir should not exceed 130 g/l, and the content of
sodium chloride below 5 10%. The content of SO4 in the reservoir and injected
waters should not exceed 80 mg/l in order to prevent the development of sulfate
reduction. The oil reservoir must be sufficiently washed to achieve a large area of
water-oil contact.

13.2 Implementation technology

Most of the developed microbiological methods of enhanced oil recovery are based
on the introduction into the reservoir as bioreagent production waste from other bio-
production applications. In this regard, the capital costs of the process consist of the
cost of shipping and injection of materials. The implementation process of microbi-
ological stimulation does not require any special equipment. Usually, the volume of
the injected liquids must be at least 0.1% of the pore volume in the area of imple-
mentation. After the bioreagent is injected, the wellhead is sealed for an incubation
period (1 2 weeks), then the area is put into operation, e.g. oil production.
Control over the process is carried out using field research methods of the oil
volume and composition in the production wells and also by hydrodynamic studies
and geophysical methods. In order for the microbiological processes in the reservoir
to not slow down it is necessary inject periodically microorganisms and nutrient
substances into the formation. The cycles of nutrient flooding are determined on the
basis of laboratory and field studies.
To improve microbiological methods of enhanced oil recovery and obtain an
integrated effect, it is advisable to combine them with other reservoir stimulation
technologies. It is well known that hydrocarbons in oil are fully reduced organic
compounds and can be oxidized by microorganisms mainly in the presence of free
oxygen, i.e. in aerobic conditions. In the anaerobic zone, in the absence of oxygen,
certain groups of fermenting microorganisms consume carbon dioxide, forming
hydrogen and methane. With an increase in the concentration of oxygen and carbon
dioxide, their metabolism rate increases to a certain maximum peak value. With a
further increase in the oxygen concentration, their metabolism rate does not change
significantly. Combining microbiological and gas formation stimulation methods
(air and/or CO 2 injections) or their alternation, a synergistic effect can be obtained.
For a detailed study of the processes, identifying the dominant mechanisms of stim-
ulation integrated methods, additional, field related, the reservoir focused research
is strongly recommended. The greatest efficiency is achieved in cases where, when
combining methods, their mutual influence on the oil immobilization mechanism is
synergetic and well balanced.
The source of energy for microbial cells, as it is well known, are the components
of organic polymers and surfactants. Sufficient availability of nutrients significantly
accelerate the processes of cell colonies growth and it increases volume of meta-
bolic products. At the same time, for the success of biochemical decomposition