Distinctive microbial communities imply the main mechanism in a MEOR trial in high pour-point reservoir

Abstract

Based on preliminary research in laboratory, a microbial enhanced oil recovery (MEOR) field trial was carried out in three production wells in Liaohe high pour-point oil reservoir. The three wells are located closely in the same block, share similar geological characteristics. Since all of them held a lower bottom temperature which accounted for serious wax precipitation underground, the microbial agents were injected to remove the waxy blockage for enhancing oil recovery. The results of the pilot showed two of the wells were effective while another well had little effect. In order to identify the functional bacteria and reveal the main mechanism of MEOR in high pour-point oil reservoirs, combined the MEOR field trial, laboratory comparative study on the positive wells and the negative well was carried out. First of all, the microbial communities in the three pilot wells were analyzed by 16S rRNA gene clone library. The results showed the original microorganisms in the two effective wells were highly similar and significantly different from those in the non-effective well. After MEOR treatment, the exogenous surfactant-producing bacteria (ESPB) and the nitrate reducing bacteria (NRB) including Lysinibacillus, Acinetobacter junnii, Sulfurihydrogenibium were abundantly stimulated and shared in the effective wells, which are thought to be the functional microorganisms in this study. Secondly, the oil components were characterized by chromatography and mass spectroscopy, the results indicated resins in the effective well samples were degraded by 5.53%–5.81% after the MEOR treatment, however, the saturated hydrocarbons exhibited little change as well as the oil pour-point. Finally, further comparative analysis for the effluents’ physical characteristics demonstrated the bio-emulsification rather than biodegradation played an important role in improving oil mobility and was the main mechanism in this trial.