Page 173 - Primer on Enhanced Oil Recovery

Microbial enhanced oil recovery (MEOR) 163

Figure 13.1 Bacteria culture liquid injection and oil permutations for microbial enhanced oil
recovery.

Thus, the following processes occur, as in stages from injection to production
well, during systemic nutrient flooding of an oil reservoir:
as a result of aerobic hydrocarbon-oxidizing microorganisms activity intermediate oxida-
2
tion products are formed. Those including acetate (CH 3 COO ) and carbon dioxide (CO 2 ),
further from the injection well, in the anaerobic zone, as a result of the activities of other
groups of microorganisms fermenters,
at the last stage, hydrogen and methane are released.
In microbiological processes evolution, the products of one bacteria population
serve as a nutrition for the next population. In this regard, the compounds formed
directly in different zones of the reservoir, have a significant impact on the physico-
chemical properties of all constituent in the oil-water-porous rock system. Acids
and alcohols, for example, dissolve carbonate rocks, prevent scaling and thus contri-
butes to an increase in porosity and higher rock permeability. Solvents are directly
involved in the oil thinning and small droplets extraction from the pores. Moreover,
solvents also change rock wettability.
During digestion of oil by microorganisms some gases are released. The gases
have a multifactorial effect on reservoir fluids: increase pressure, change pH and
viscosity of water, compressibility of oil and saturation pressure. The changes go