Microbial enhanced oil recovery (MEOR) technology has advanced from laboratory based studies in the early 1980's to field applications in the 1990's. Researchers in the United States and Europe have examined a variety of technical approaches to MEOR including treatment of injector or producing wells. EBT in collaboration with an oil company has recently completed a technical review of this field and is designing a field demonstration project for its client.
MEOR processes involve the use of reservoir microorganisms or specially selected natural bacterial to produce specific metabolic events that lead to enhanced oil recovery. The mechanism by which MEOR processes work can be quite complex and may involve multiple biochemical processes. In selective plugging approaches, microbial cell mass or biopolymers plug high permeability zones and lead to a redirection of the water flood. In other processes, biosurfactants are produced in situ which leads to increased mobilization of residual oil. In still other processes, microbial production of carbon dioxide and organic solvents reduces the oil viscosity as the primary mechanism for EOR. In a MEOR process, conditions for microbial metabolism are supported via injection of nutrients. In some processes, this involves injecting a fermentable carbohydrate into the reservoir. Some reservoirs also require inorganic nutrients as substrates for cellular growth or for serving as alternative electron acceptors in place of oxygen or carbohydrates. In general, researchers have found that MEOR processes are applicable to 40-50% of North American oil reservoirs. Reservoir conditions which restrict MEOR applications are high total salinity (above 12%), high reservoir temperatures (above 50 C) and very low permeability. While microbes are known to grow under conditions outside of these mentioned ranges of environmental parameters, most MEOR field demonstration projects have been in reservoirs with the above conditions.
Field MEOR projects have been conducted in the United States, Australia, China, Rumania and Russia. These projects report beneficial results in most cases. Reported enhanced oil production resulting from MEOR processes vary from no impact to 13%, 19%, 36%, 50-65% and 204%. In addition to increased oil production, some projects report decreased water production, increased GOR and improved injectivity.