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After conventional oil recovery operations, more than half of the crude oil still remains in a form, which is difficult to extract. Therefore, exploring and developing new enhanced oil recovery (EOR) technologies have always been priority research in oilfield development. Microbial enhanced oil recovery (MEOR) is a promising tertiary oil recovery technology that has received widespread attention from the global oil industry in recent years due to its environmental friendliness, simplicity of operation, and cost-effectiveness. This review presents the: principle, characteristics, classification, recent development, and applications of MEOR technology. Based on hundreds of field trials conducted worldwide, the microbial strains, nutrient systems, and actual effects used in these technologies are summarized, with an emphasis on the achievements made in the development and application of MEOR in China in recent years. These technical classifications involve: microbial huff and puff recovery (MHPR), microbial flooding recovery (MFR), microbial selective plugging recovery (MSPR), and microbial wax removal and control (MWRC). Most of them have achieved good results, with a success rate of approximately 80%. These successful cases have accumulated into rich experiential indications for the popularization and application of MEOR technology, but there are still important yet uncertain factors that hinder the industrialization of this technology. Finally, based on the extensive research and development of MEOR by the authors, especially in both laboratory and industrial large scales, the main challenges and future perspectives of the industrial application for MEOR are presented. [ABSTRACT FROM AUTHOR]

The article reviews the usage of microbial surface active compounds (SAC) in reducing the negative environmental impact of water insoluble pollutants. Topics discussed include bioremediation of oil spills which consists of volatile organic compounds and polycyclic aromatic hydrocarbons, bioremediation of oil contaminated soil, microbial enhanced oil recovery with bioemulsifiers, bioremediation of heavy metals with biosurfactants, removal of chlorinated compounds and detergent pollution control.

Aims Microbial enhanced oil recovery (MEOR) is dedicated to enhancing oil recovery by harnessing microbial metabolic activities and their byproducts within reservoir rocks and fluids. Therefore, the investigation of microbial mobility and their extensive distribution within crude oil is of paramount importance in MEOR. While microscale models have been valuable for studying bacterial strain behavior in reservoirs, they are typically limited to 2D representations of porous media, making them inadequate for simulating actual reservoir conditions. Consequently, there is a critical need for 3D models and dependable visualization methods to observe bacterial transport and metabolism within these complex reservoir environments. Methods and results Bacterial cellulose (bc) is a water-insoluble polysaccharide produced by bacteria that exhibits biocompatibility and biodegradability. It holds significant potential for applications in the field of MEOR as an effective means for selective plugging and spill prevention during oil displacement processes. Conditionally cellulose-producing strain, FY-07-G, with green fluorescent labeling, was engineered for enhanced oil recovery. 3D micro-visualization model was constructed to directly observe the metabolic activities of the target bacterial strain within porous media and to assess the plugging interactions between cellulose and the medium. Additionally, X-ray computed tomography (X-CT) technology was employed for a comprehensive analysis of the transport patterns of the target strain in oil reservoirs with varying permeabilities. The results indicated that FY-07-G, as a microorganism employing biopolymer-based plugging principles to enhance oil recovery, selectively targets and seals regions characterized by lower permeability and smaller pore spaces. Conclusions This work provided valuable insights into the transport and metabolic behavior of MEOR strains and tackled the limitation of 2D models in faithfully replicating oil reservoir conditions, offering essential theoretical guidance and insights for the further application of oil-displacing bacterial strains in MEOR processes. [ABSTRACT FROM AUTHOR]

Recently, nanofluids and microorganisms -as environmentally friendly agents- have indicated superb potential in the enhanced oil recovery process. Herein, the interface properties of nanofluid and rock surfaces were surveyed by a synergistic combination of nano and biomaterials. The stability of the synthesized TiO 2 nanofluid with the aid of steric and electrostatic methods (at 25 and 80 °C) was studied by sedimentation tests, particle size distribution, and zeta potential analysis. The growth rate of bioproducts from three bacteria (Acinetobacter, Bacillus, and Klebsiella) in different carbon sources was optimized. The high stability of nanofluid was achieved by the use of sodium dodecyl sulfate surfactant and pH = 8 for 30-day at temperatures of 25 °C and 80 °C as the base fluid. The optimal growth media for bacteria is a 3-day incubation at 37 °C in a shaking incubator with whey as the carbon source. Finally, the simultaneous use of nano (0.005 wt%) and biomaterials (0.01 wt%) showed the highest wettability alteration, transforming it from strongly oil-wet to water-wet at an optimal concentration of materials. Overall, the findings of this study can help to reduce environmental concerns and operating expenses. [Display omitted] • Use of Nano and biomaterials simultaneously for EOR at temperatures of 25 and 80 °C. • Three bacteria were screened in various culture media for MEOR applications. • Preparation of a stable nanofluid via the steric and electrostatic methods. • Whey is a better carbon source for biosurfactant production. • The synergistic of nano and biomaterials revealed an 80% wettability alternation. [ABSTRACT FROM AUTHOR]

Heavy oil has hindered crude oil exploitation and pollution remediation due to its high density and viscosity. Bioemulsifiers efficiently facilitate the formation and stabilization of oil-in-water emulsions in low concentrations thus eliminating the above bottleneck. Despite their potential benefits, various obstacles had still impeded the practical applications of bioemulsifiers, including high purification costs and poor adaptability to extreme environments such as high temperature and oxygen deficiency. Herein, thermophilic facultative anaerobic Geobacillus thermodenitrificans NG80–2 was proved capable of emulsifying heavy oils and reducing their viscosity. An exocelluar bioemulsifier could be produced by NG80–2 using low-cost lignocellulose components as carbon sources even under anaerobic condition. The purified bioemulsifier was proved to be polysaccharide-protein complexes, and both components contributed to its emulsifying capability. In addition, it displayed excellent stress tolerance over wide ranges of temperatures, salinities, and pHs. Meanwhile, the bioemulsifier significantly improved oil recovery and degradation efficiency. An eps gene cluster for polysaccharide biosynthesis and genes for the covalently bonded proteins was further certificated. Therefore, the bioemulsifier produced by G. thermodenitrificans NG80–2 has immense potential for applications in bioremediation and EOR, and its biosynthesis pathway revealed here provides a theoretical basis for increasing bioemulsifier output. [Display omitted] • NG80-2 produces glycoprotein emulsifier anaerobically from lignocellulose biomass. • The bioemulsifier exhibited excellent capability of heavy oil viscosity reduction. • A novel eps cluster for bioemulsifier synthesis was identified and characterized. • The protein fractions of bioemulsifier showed outstanding emulsifying activity. • The bioemulsifier significantly improved oil degradation and recovery efficiency. [ABSTRACT FROM AUTHOR]

Biosurfactant is an important amphiphilic microbial product, which plays an important role in microbial enhanced oil recovery (MEOR) by reducing crude oil-water interfacial tension (IFT), emulsification and wettability alternation. Compared with chemical surfactants, biosurfactants have the advantages of lower toxicity and higher biodegradability, but the relatively low yield also limits their applications. In this study, the influence of hydrocarbon carbon sources on the production of biosurfactants by Bacillus licheniformis L20 was investigated, and the variable of unit biosurfactant concentration was proposed to optimize the biosurfactant production medium. The highest concentration was obtained in LB/MSS-K medium, which was up to 1.225 g/L. The biosurfactant produced by Bacillus licheniformis L20 in that medium was characterized as lipopeptide via using FTIR. This biosurfactant shown stable emulsifying properties for different hydrocarbons and crude oils, but it can not reduce the oil-water IFT significantly. However, after mixed biosurfactant with chemical anionic surfactants (1,3-diacylglycerols-2-sulfate) and nonionic surfactant (fatty alcohol-polyoxyethylene ether), the anionic surfactant/biosurfactant mixed system can reduce the crude oil-water IFT to 0.109 mN/m. In addition, the emulsification stability of the biosurfactant mixed system were determined, the results shown that the emulsion formed by the nonionic surfactant/biosurfactant mixed system or the anionic surfactant/biosurfactant mixed system can remain stable under a wide range of temperature, pH and NaCl concentration, respectively. Furthermore, the performance of chemical surfactant/biosurfactant mixed system were evaluated, the results shown that anionic surfactant/biosurfactant mixed system and nonionic surfactant/biosurfactant mixed system can increase the oil recovery rate by 24.12% and 21.67% respectively after water flooding, while the biosurfactant used alone was only 19.58%. Thus, the results obtained from this work shown that anionic surfactant/biosurfactant mixed system have good prospect of application in ex-situ MEOR. • Effect of hydrocarbon carbon sources on biosurfactants production was investigated. • Interfacial activity of anionic or nonionic/biosurfactant mixed system was studied. • These mixed system led to higher oil recovery rate than biosurfactant used alone. [ABSTRACT FROM AUTHOR]

The microbial enhanced oil recovery (MEOR) process has been identified as a promising alternative to conventional enhanced oil recovery methods because it is eco-friendly and economically advantageous. Despite its various advantages, the technique is not widely applied because the reservoir conditions such as temperature, pressure, and salinity are extremely harsh for microbial survival. In this study, an accurate microbiological model incorporating the environmental effects has been developed. The efficiency of the MEOR process based on selective plugging by microbial biopolymer generation has been examined in multi-layered systems with high permeability contrast. The MEOR is applied to multi-layered reservoirs of different environmental conditions. When the MEOR is applied to a high temperature reservoir, there is an optimum injection temperature that can greatly improve the oil production. Oil productivity in a high-pressure reservoir is estimated to decrease by 15% when the pressure effect is considered. We simulated different salinity conditions and showed that oil recovery decreased with increasing salinity and only was affected by injected water salinity. The oil recovery obtained by the developed model included all three environmental effects and provided estimates 21% lower than that of a previous model that did not account for the environmental effects. • Modelling the growth rate of microorganisms according to temperature, pressure, and salinity conditions. • Analysis of MEOR effect based on biological clogging at various reservoir temperatures. • Analysis of the effect of pressure on microbial growth and MEOR. • Comparison of effects according to injection salinity when the MEOR is applied. • The importance of modelling considering environmental conditions in MEOR. [ABSTRACT FROM AUTHOR]