Enrichment culture has been carried out to develop microorganisms for MEOR. In the 1st report, it was reported that 49 samples were collected and 41 samples developed cultures with kerosene as substrates at 30°C, It was also reported that the growth rate, pH and IFT as well as the salt tolerance were used as representatives of the function of bacteria for selection, and 8 cultures were finally selected.
In the 2nd report, 4 cultures out of 8 reported in the 1st report were chosen for isolation and 4 isolated bacteria were used for investigating the influence of concentration of metal ions generally present in the water of oil field.
In these studies, bacteria obtained show functional characteristics for EOR at some degree but not outstandingly. This may be attributed to the unsatisfactory nature of kerosene as substrates.
In the present study, the yeast extract was added to the liquid medium as well as kerosene and the effect was investigated for 4 bacteria used in the previous study, from the viewpoint of functional characteristics for MEOR. Results are summarised as follows;
1. Growth became more active for all bacteria and the concentration reached 10
8-10
9 cells/m
l in 1 to 2 days. The growth rate increased 3.8 to 9.1 times to that in culture with only kerosene as substrate.
2. The maximum concentration was 7×10
8 to 5×10
9 cells/m
l, which was insignificantly higher than that in case of kerosene only.
3. The pH of the liquid mediums at the end of the culture was 7 to 8.5.
4. IFT between kerosene and liquid medium after 2 week culture decreased from several 10 mN/m to 1mN/m. Particularly 2-F shows IFT less than 0.1mN/m, which implies the useful character for MEOR.
From results summarised above, it may be concluded that the adding the yeast extract to the liquid medium with kerosene is effectve for MEOR.
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