Long-Term Pore-Scale Experiments on MEOR by Surfactant-Producing Microorganisms Reveal the Altering Dominant Mechanisms of Oil Recovery

Abstract

During microbial-enhanced oil recovery (MEOR), surfactant-producing microorganisms are reported to improve displacement efficiency. However, the sweep efficiency could be improved by emulsified droplets or be reduced by low-IFT (interfacial tension)-induced fingering flow. Therefore, whether sweep efficiency can be improved by surfactant-producing microorganisms is currently unclear. To reveal the EOR mechanisms by surfactant-producing microorganisms, a 2D micro-model was used to conduct a long-term pore-scale experiment. In the results, 19.4% of the original oil in place (OOIP) was recovered, and surfactant-producing microorganisms can improve not only displacement efficiency (16.9% of the OOIP in the main stream) but also sweep efficiency (27.7% of the OOIP in the margin). Furthermore, the sweep efficiency was improved during flooding and shut-in periods. For instance, 19.5% of the OOIP in margins migrated to the main stream during the 1st shut-in period. Regarding mechanisms of sweep, it was improved by Jamin’s effect during the flooding period, while during the shut-in period, the oil migration was attributed to the spontaneously spreading biomass and their wettability altering the biosurfactant. This long-term experiment revealed that the dominant oil recovery mechanisms were altering with declining oil saturation, based on which sweep efficiency contributed to oil recovery only at oil saturation higher than 40.5%. While at lower oil saturation, only displacement efficiency could be improved.