Abstract
Among 64 bacterial strains isolated in this study, the best two of biosurfactant-producing bacteria were selected and identified based on the phenotypic properties and molecular approach based on 16S rRNA having 100% similarity to the gram-negative Enterobacter aerogenes B19 strain bacteria and rode gram-positive strain Bacillus cereus ISU-02 in the Nucleotide database of the National Center for Biotechnology Information. The study showed that two selected isolates gave the highest positive results that were used to investigate the biosurfactant production including: interfacial reduction, foaming activity, hemolytic activity, CTAB agar plate, drop collapse assay, oil displacement test and emulsification index E24%. Both Bacillus cereus ISU-02 strain and Enterobacter aerogenes B19 strain have reduced the interfacial tension to 27.61 and 28.93, respectively. Biosurfactants produced from both isolates were tested for oil recovery using spontaneous imbibition process. Bacillus cereus ISU-02 strain gave the highest oil recovery of 66.9% for rock permeability of 843 mD, followed by Enterobacter aerogenes B19 strain with oil recovery of 34% for rock permeability 197 mD, while the lowest rate of oil recovery was 12.1% for FW with permeability of 770 mD. An additional oil rate reached to 7.9% has been recovered from the residual oil when the core plug that was treated with formation water alone was retreated with the cell free biosurfactant supernatant. Use of the new biosurfactants has improved oil recovery better than use of formation water alone or formation water with the commercial surfactant SDS.
Highlights
In most of oil fields, only a small portion of crude oil can be recovered by traditional recovery methods
Enhanced oil recovery (EOR) techniques are used to recover the residual oil from reservoir rocks after the primary or secondary stages
5 ml of produced water was added to Erlenmeyer flask size 250 ml containing 95 ml of mineral estimated media (MSM) composed of 2% of crude oil as a carbon source, 1 g/L K H2PO4, 6 g/L NaNO3, 1 g/L K 2HPO4, 0.02 g/L F eSO4, 0.5 g/L M gSO4 and 0.02 g/L Na2MoO4 at a pH of 7.0–7.2 at a pH of 7.0–7.2 (Zhao et al 2017)
Summary
In most of oil fields, only a small portion of crude oil can be recovered by traditional recovery methods. After the primary and secondary recovery, up to 66% of oil stays caught in the reservoir rocks (Nnaemeka et al 2018). Water flooding is the most important technique in the secondary recovery stage. This technique includes injecting water in hydrocarbon-bearing zones through a series of injection wells to sweep the trapped oil toward producing wells (Nikzad Amoli 2011). Enhanced oil recovery (EOR) techniques are used to recover the residual oil from reservoir rocks after the primary or secondary stages. One of EOR methods is injection of surfactants with water to improve the sweep efficiency of water flooding technique (Sheng 2010). Surfactants play an active role in enhanced spontaneous imbibition in oil
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