Abstract
Surfactin, which is an anionic bio-surfactant, can be effective for enhanced oil recovery because it decreases interfacial tension between oil and water. However, it forms precipitation by binding with divalent cations. This study examined the countermeasure to prevent surfactin from forming precipitation for applying it to enhanced oil recovery. Alcohols, chelating agents, a cationic surfactant and an ion capturing substance were selected as the candidates for inhibiting surfactin from forming precipitation. Citric acid and trisodium citrate were selected as promising candidates through the measurements of turbidity of the mixture of the candidate, surfactin and calcium ions. Those chemicals also had a function as a co-surfactant for surfactin. However, the permeability of the Berea sandstone core into which the solution containing surfactin and trisodium citrate was injected was decreased significantly, whereas citric acid could be injected into the core without significant permeability reduction. Citric acid was therefore selected as the best inhibitor and subjected to the core flooding experiments. High enhancement of oil recovery of 9.4% (vs. original oil in place (OOIP)) was obtained and pressure drop was not increased during the injection of surfactin and citric acid. Those results suggest that citric acid has a dual role as the binding inhibitor and co-surfactant for surfactin.
Highlights
Surfactant is used for enhanced oil recovery (EOR) because it has capabilities to reduce interfacial tension (IFT) between oil and water and improves the replacement efficiency of oil [1]
The turbidity of the solution containing citric acid, trisodium citrate extremely low lowas ascompared comparedwith withthat that of citric acid, trisodium citrateororpentasodium pentasodiumtriphosphate triphosphate was was extremely of the solution containing other candidates. These results indicate that those three candidates successfully prevented the surfactin from forming precipitation of surfactin calcium
These results suggest that the citric acid is an effective additive for applying surfactin to enhanced enhanced oil recovery techniques in oil reservoirs containing divalent cations
Summary
Surfactant is used for enhanced oil recovery (EOR) because it has capabilities to reduce interfacial tension (IFT) between oil and water and improves the replacement efficiency of oil [1]. A lot of field trials of surfactant EOR have been performed in many countries and great enhancement of oil recovery has been reported in almost all the field trials [2,3,4,5,6,7,8,9,10,11]. Anionic surfactant is the most popular surfactant for EOR because it has the highest capability to reduce IFT between oil and water in the three types of surfactant. Different types of anionic surfactant are used for EOR around the world [12]; it still has several challenges in order to be more effectively used for EOR.
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