Microorganisms provide a unique opportunity for improving oil recovery economically and environmentally in a technique called “Microbial Enhanced Oil Recovery MEOR”. This study highlights the importance and potential of microbiology in petroleum engineering. Biosurfactant production is one of the most efficient mechanisms in microbial enhanced oil recovery (MEOR) processes. Biosurfactants have recently attained extended attention because they have numerous benefits over chemical synthetic surfactants, including higher biodegradability, lower toxicity, higher foaming, environmental compatibility, and effective properties under harsh conditions.
The present study investigates the production of biosurfactants by indigenous bacteria isolated from Egyptian oil fields, and the use of these biosurfactants in enhancing the oil recovery. Fifty-nine Egyptian oil reservoirs were screened to investigate the potential for MEOR in Egyptian oil fields. The results showed that 8 reservoirs from the Gulf of Suez and 3 reservoirs from the Western Desert had the potential for MEOR. The bacterial isolation and identification of the collected crude oil samples from the Egyptian oil fields that have the potential for MEOR showed 11 isolated strains, which are Pseudomonas stutzeri, Clostridium spp, pseudomonas aeruginosa, pseudomonas fluorescens, Brevibacterium spp, Cellulosimicrobium spp, Pseudomonas panipatensis, Enterobacter spp, Bacillus flexus, Bacillus licheniformis, and Bacillus subtilis. The isolated strains Bacillus subtilis and Bacillus licheniformis were selected for further studies in this research because they are reported as good biosurfactants-producing bacteria under facultative or anaerobic conditions, spore forming, and non-pathogenic. The results of surface activity and bacteria growth examination also showed that the selected bacterial strains Bacillus licheniformis and Bacillus subtilis could produce effective biosurfactants that reached their maximum surface activity and reach maximum after 24 h of incubation. The results of emulsification activity examination showed that produced biosurfactants by Bacillus licheniformis and Bacillus subtilis could significantly emulsify crude oil with emulsification indices of 50% and 64%, respectively.
The contact angle measurement showed that the oil was more detached from the sandstone surface when submerged in an aqueous solution of the produced biosurfactants, where the biosurfactants produced by Bacillus subtilis and Bacillus licheniformis decreased the contact angle of the oil drop from 104.96° and 107.30° to 85.40° and 88.72° after 24 h, respectively. Similarly, the new proposed medium decreased the contact angle of the oil drop from 112.30° and 110.90° to 63.85° and 69.33° after 24 h, respectively, which could facilitate the recovery of remaining oil. High stability was observed at high temperatures for a long-time period and more than 60% of their surface and emulsification activities were maintained over a wide range of pH and salinity. The core flooding tests showed the potential of the biosurfactants produced by Bacillus licheniformis and Bacillus subtilis to recover up to 31% and 39% of additional oil over the water flooding residual oil saturation under simulated reservoir conditions, respectively. In addition to the beneficial effects of the selected indigenous bacteria in producing effective biosurfactants, the performed environmental risk assessment showed that Bacillus licheniformis and Bacillus subtilis are environmentally safe, have no potential for toxicity, and no risk could occur for MEOR.