Experimental Investigations of Behaviour of Biosurfactants in Brine Solutions Relevant to Hydrocarbon Reservoirs

Abstract

In this study, we investigated the behaviour of rhamnolipid and Greenzyme in brine solutions relevant to hydrocarbon reservoir. Prior to this work, several studies only reported the behaviour of the biosurfactants dissolved in sodium chloride solutions of varied salinity. The results of this study are relevant to the application of the biosurfactants in enhanced oil recovery, during which the compounds are injected into reservoir saturated with formation water, typically of high salinity and complex composition. Surface tension and conductivity methods were used to determine the critical micelle concentrations of the biosurfactants, Gibbs surface excess concentrations and standard free energy at water-air interface. The results show that rhamnolipid and Greenzyme could reduce the surface tension of water from 72.1 ± 0.2 mN/m to 34.7 ± 0.4 mN/m and 47.1 ± 0.1 mN/m respectively. They were also found to be stable in high salinity and high temperature with rhamnolipid being sensitive to brine salinity, composition and pH while Greenzyme showed tolerance for high salinity. Furthermore, the Gibbs standard free energy of micellisation shows that rhamnolipid and Greenzyme have the tendency to spontaneously form micelles with rhamnolipid showing more surface adsorption. However from maximal Gibbs surface excess concentration calculations, Greenzyme monomers tend to favour aggregation more than that of rhamnolipid.

A Synergy between Controlled Salinity Brine and Biosurfactant Flooding for Improved Oil Recovery: An Experimental Investigation Based on Zeta Potential and Interfacial Tension Measurements

“…Also, our choice of dilution factor was based on the stability of biosurfactants in injected brines. Biosurfactant precipitation was observed in brines of salinity higher than 0.0083 M in previously published study carried out with the same materials [38]. The rock sample used in this study is Estaillades limestone from France.…”

“…This can be associated with the observed changes in the rhamnolipid solution (Figure 3(e)) that impeded further imbibition process. Rhamnolipid tends to precipitate in high salinity medium due to its composition [38] and this was evident in the observed change in brine solution during CSBS-R imbibition. This suggests that application of rhamnolipid in oil reservoirs to improve oil recovery may be associated with its precipitation; hence adequate compatibility test is recommended before reservoir application.…”

“…Also, the use of CSBS-G and CSBS-R increases oil recovery relative to FMB and CSB applications with CSBS-R process being characterised by fastest imbibition rate. This effect is attributable to its high surface activity that enhances oil-brine IFT reduction and increase in capillary effect [34,38].…”

“…Expectantly, application of rhamnolipid with capacity to generate lower IFT ought to result in higher recovery, but contrary was the case. This variance can be attributed to high sensitivity of rhamnolipid to high salinity as evident by its precipitation in such medium (more details are available in [38]). Core flooding is a dynamic process characterised by continuous mixing and diffusion of injected fluid with connate water saturation in the core.…”

Microbial Surfactants: The Next Generation Multifunctional Biomolecules for Diverse Applications

“…Introducing crude biosurfactants alongside with the surfactant producing microorganisms will improve performance efficiency. This is because biosurfactants are tolerant to a wide range of physicochemical and environmental changes such as high salinity (≤ 20%), pH (2-12) and temperature (30-100 °C) [62,63] as evident in reservoirs. By virtue of fitness and adaptability, the co-introduced microorganisms would keep producing biosurfactants in the formation.…”