ABSTRACT
The in situ microbiologically enhanced oil recovery (MEOR) consists of introducing relatively low concentrations of living, surfactant-producing organisms into the reservoir. The extra situm technique is a compromise between the chemical and the in situ biological process. The required surfactant is produced biologically at the surface. The in situ technique produces the required surfactant in the reservoir rock, while the extra situm method introduces the surfactant as solution already produced in a surface installation. Conflicting reports on organisms surviving or even having an optimal temperature for their growth above 250°C have been published. The effects of pressure and the mechanism responsible for such effects are not well understood. The effectiveness of the biologically produced surfactants will be equally governed by the pH of the environment. A variety of effects attributed to high salinity has been described and discussed by Krushner. An introduction of a selective substrate not acceptable to the endogenous population may favor the establishment of the introduced organisms.
