Abstract
For microbial enhanced oil recovery (MEOR), different mechanisms have been introduced. In some of these papers, the phenomena and mechanisms related to biosurfactants produced by certain microorganisms were discussed, while others studied the direct impacts of the properties of microorganisms on the related mechanisms. However, there are only very few papers dealing with the direct impacts of microorganisms on interfacial properties. In the present work, the interfacial properties of three bacteria MJ02 (Bacillus Subtilis type), MJ03 (Pseudomonas Aeruginosa type), and RAG1 (Acinetobacter Calcoaceticus type) with the hydrophobicity factors 2, 34, and 79% were studied, along with their direct impact on the water/heptane interfacial tension (IFT), dilational interfacial visco-elasticity, and emulsion stability. A relationship between the adsorption dynamics and IFT reduction with the hydrophobicity of the bacteria cells is found. The cells with highest hydrophobicity (79%) exhibit a very fast dynamic of adsorption and lead to relatively large interfacial elasticity values at short adsorption time. The maximum elasticity values (at the studied frequencies) are observed for bacteria cells with the intermediate hydrophobicity factor (34%); however, at longer adsorption times. The emulsification studies show that among the three bacteria, just RAG1 provides a good capability to stabilize crude oil in brine emulsions, which correlates with the observed fast dynamics of adsorption and high elasticity values at short times. The salinity of the aqueous phase is also discussed as an important factor for the emulsion formation and stabilization.
Highlights
For most of the oil reservoirs, just a small percentage of the original oil in place can be extracted via the natural pressure of the reservoir, combined with gravitational drainage and supported by external forces like pumps
Microorganism Growth Conditions The cultures were grown at 35 ◦C in Luria Bertani medium (LB), which is composed of tryptone, 10 g/L; yeast extract, 5 g/L; NaCl, 5 g/L; on a rotary shaker at 160 rpm; the cells, at the start of their stationary phase, were subsequently harvested by centrifugation at 8000× g
The results of the BATH tests illustrate a wide hydrophobicity range between 2 and 79% for the selected bacteria (Table 1), which is suitable for investigating the effect of hydrophobicity of bacteria cells on the interfacial properties
Summary
For most of the oil reservoirs, just a small percentage (less than 20%) of the original oil in place can be extracted via the natural pressure of the reservoir, combined with gravitational drainage and supported by external forces like pumps. Extensive studies have been performed to find methods of enhanced oil recovery (EOR), and even a 1% improvement can be an important achievement for large scale oil reservoirs Most of these methods are not yet economically feasible or environmentally friendly [1] for practical applications in the field, and successful projects are often case study dependent. Dorobantu et al showed that the hydrophobic strain, Acinetobacter venetianus RAG-1, stabilizes both oil in water and water in oil emulsions without affecting the IFT [15]. Kang et al showed that the presence of two different strains, A. venetianus RAG-1 and R. erythropolis 20S-E1-c, has negligible effects on the oil/water IFT, changing IFT values only from 52 mN/m to 49 ± 1.5 mN/m and 48.5 ± 1.2 mN/m, respectively [17]. Colloids Interfaces 2021, 5, 49 elasticity values of the related solutions, as key factors in the discussed mechanism, are investigated in this work
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