Department of Chemical and Petroleum Engineering,Sharif University of Technology
Rock samples from the Asmary outcrop formation of the Ahwaz oil rich zone with a porosity of 16\% and permeability of 1 md and MIS crude oil with an API value of 42.5 and moderate asphaltene content of 3\%, were used to study the effect of the incubation time and flow rate of the displacing fluid in MEOR operations. Five species of rod shaped, gram positive, thermophile and facultative bacteria were isolated and purified from the crude. Due to the high sweep efficiency prevailing in the core flooding system, the effect of the displacing brine flow rate on the oil recovery efficiency was found not to be significant. On the other hand, a 100\% increase in incubation time from 7 to 14 days resulted in an increase from 3\% to 4\% in the total cumulative production. Application of a cyclic operation was not effective in promoting the efficiency of the MEOR operation, probably due to the stronger effect of flooding on the removal of valuable metabolites, as compared to undesired ones, before the stationary phase of the microbial kinetics. While qualitative measurements did not show a strong change in the water-rock contact angle, more than a 4-fold increase in capillary number occurred after microbial treatment, implying that reduction of interfacial tension was the stronger mechanism of oil recovery in this work.