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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]

Abstract Background Surfactin, a representative biosurfactant of lipopeptide mainly produced by Bacillus subtilis, consists of a cyclic heptapeptide linked to a β-hydroxy fatty acid chain. The functional activity of surfactin is closely related to the length and isomerism of the fatty acid chain. Results In this study, the fatty acid precursor supply pathway in Bacillus subtilis 168 for surfactin production was strengthened through two steps. Firstly, pathways competing for the precursors were eliminated with inactivation of pps and pks. Secondly, the plant medium-chain acyl-carrier protein (ACP) thioesterase (BTE) from Umbellularia californica was overexpressed. As a result, the surfactin titer after 24 h of cultivation improved by 34%, and the production rate increased from 0.112 to 0.177 g/L/h. The isoforms identified by RP-HPLC and GC–MS showed that the proportion of nC14-surfactin increased 6.4 times compared to the control strain. A comparison of further properties revealed that the product with more nC14-surfactin had higher surface activity and better performance in oil-washing. Finally, the product with more nC14-surfactin isoform had a higher hydrocarbon-emulsification index, and it increased the water-wettability of the oil-saturated silicate surface. Conclusion The obtained results identified that enhancing the supply of fatty acid precursor is very essential for the synthesis of surfactin. At the same time, this study also proved that thioesterase BTE can promote the production of nC14-surfactin and experimentally demonstrated its higher surface activity and better performance in oil-washing. These results are of great significance for the MEOR application of surfactin. Graphic abstract

Background: Surfactin, a representative biosurfactant of lipopeptide mainly produced by Bacillus subtilis, consists of a cyclic heptapeptide linked to a β-hydroxy fatty acid chain. The functional activity of surfactin is closely related to the length and isomerism of the fatty acid chain. Results: In this study, the fatty acid precursor supply pathway in Bacillus subtilis 168 for surfactin production was strengthened through two steps. Firstly, pathways competing for the precursors were eliminated with inactivation of pps and pks. Secondly, the plant medium-chain acyl-carrier protein (ACP) thioesterase (BTE) from Umbellularia californica was overexpressed. As a result, the surfactin titer after 24 h of cultivation improved by 34%, and the production rate increased from 0.112 to 0.177 g/L/h. The isoforms identified by RP-HPLC and GC–MS showed that the proportion of nC14-surfactin increased 6.4 times compared to the control strain. A comparison of further properties revealed that the product with more nC14-surfactin had higher surface activity and better performance in oil-washing. Finally, the product with more nC14-surfactin isoform had a higher hydrocarbon-emulsification index, and it increased the water-wettability of the oil-saturated silicate surface. Conclusion: The obtained results identified that enhancing the supply of fatty acid precursor is very essential for the synthesis of surfactin. At the same time, this study also proved that thioesterase BTE can promote the production of nC14-surfactin and experimentally demonstrated its higher surface activity and better performance in oil-washing. These results are of great significance for the MEOR application of surfactin. [ABSTRACT FROM AUTHOR]

Surfactants are a group of amphiphilic chemical compounds (i.e., having both hydrophobic and hydrophilic domains) that form an indispensable component in almost every sector of modern industry. Their significance is evidenced from the enormous volumes that are used and wide diversity of applications they are used in, ranging from food and beverage, agriculture, public health, healthcare/medicine, textiles, and bioremediation. A major drive in recent decades has been toward the discovery of surfactants from biological/natural sources—namely bio-surfactants—as most surfactants that are used today for industrial applications are synthetically-manufactured via organo-chemical synthesis using petrochemicals as precursors. This is problematic, not only because they are derived from non-renewable resources, but also because of their environmental incompatibility and potential toxicological effects to humans and other organisms. This is timely as one of today's key challenges is to reduce our reliance on fossil fuels (oil, coal, gas) and to move toward using renewable and sustainable sources. Considering the enormous genetic diversity that microorganisms possess, they offer considerable promise in producing novel types of biosurfactants for replacing those that are produced from organo-chemical synthesis, and the marine environment offers enormous potential in this respect. In this review, we begin with an overview of the different types of microbial-produced biosurfactants and their applications. The remainder of this review discusses the current state of knowledge and trends in the usage of biosurfactants by the Oil and Gas industry for enhancing oil recovery from exhausted oil fields and as dispersants for combatting oil spills.

Rhamnolipids (RMLs) have more effectiveness for specific uses according to their homologue proportions. Thus, the novelty of this work was to compare mono‐RMLs and di‐RMLs physicochemical properties on microbial enhanced oil recovery (MEOR) applications. For this, RML produced by three strains of Pseudomonas aeruginosa containing different homologues proportion were used: a mainly mono‐RMLs producer (mono‐RMLs); a mainly di‐RMLs producer (di‐RMLs), and the other one that produces relatively balanced amounts of mono‐RML and di‐RML homologues (mono/di‐RML). For mono‐RML, the most abundant molecules were Rha‐C10C10 (m/z 503.3), for di‐RML were RhaRha‐C10C10 (m/z 649.4) and for Mono/di‐RML were Rha‐C10C10 (m/z 503.3) and RhaRha‐C10C10 (m/z 649.4). All RMLs types presented robustness under high temperature and variation of salinity and pH, and high ability for oil displacement, foam stability, wettability reversal and were classified as safe for environment according to the European Union Directive No. 67/548/EEC. For all these properties, it was observed a highlight for mono‐RML. Mono‐RML presented the lowest surface tension (26.40 mN/m), interfacial tension (1.14 mN/m), and critical micellar concentration (CMC 27.04 mg/L), the highest emulsification index (EI24 100%) and the best wettability reversal (100% with 25 ppm). In addition, mono‐RML showed the best acute toxicity value (454 mg/L), making its application potential even more attractive. Based on the results, it was concluded that all RMLs homologues studied have potential for MEOR applications. However, results showed that mono‐RML stood out and have the best mechanism of oil incorporation in micelles due their most effective surface‐active physicochemical features. [ABSTRACT FROM AUTHOR]

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.

Utilization of low-cost, environmental-friendly microbial enhanced oil recovery (MEOR) techniques in thermal recovery-processed oil reservoirs is potentially feasible. However, how exogenous microbes facilitate crude oil recovery in this deep biosphere, especially under mesophilic conditions, is scarcely investigated. In this study, a thermal treatment and a thermal recurrence were processed on crude oil collected from Daqing Oilfield, and then a 30-day incubation of the pretreated crude oil at 37 °C was operated with the addition of two locally isolated hydrocarbon-degrading bacteria, Amycolicicoccus subflavus DQS3-9A1T and Dietzia sp. DQ12-45-1b, respectively. The pH, surface tension, hydrocarbon profiles, culture-dependent cell densities and taxonomies, and whole and active microbial community compositions were determined. It was found that both A. subflavus DQS3-9A1T and Dietzia sp. DQ12-45-1b successfully induced culture acidification, crude oil bioemulsification, and residual oil sub-fraction alteration, no matter whether the crude oil was thermally pretreated or not. Endogenous bacteria which could proliferate on double heated crude oil were very few. Compared with A. subflavus, Dietzia sp. was substantially more effective at inducing the proliferation of varied species in one-time heated crude oil. Meanwhile, the effects of Dietzia sp. on crude oil bioemulsification and hydrocarbon profile alteration were not significantly influenced by the ploidy increasing of NaCl contents (from 5 g/L to 50 g/L), but the reconstructed bacterial communities became very simple, in which the Dietzia genus was predominant. Our study provides useful information to understand MEOR trials on thermally processed oil reservoirs, and proves that this strategy could be operated by using the locally available hydrocarbon-degrading microbes in mesophilic conditions with different salinity degrees.

Crude oil is a major energy source that is exploited globally to achieve economic growth. To meet the growing demands for oil, in an environment of stringent environmental regulations and economic and technical pressure, industries have been required to develop novel oil salvaging techniques. The remaining ~70% of the world’s conventional oil (one-third of the available total petroleum) is trapped in depleted and marginal reservoirs, and could thus be potentially recovered and used. The only means of extracting this oil is via microbial enhanced oil recovery (MEOR). This tertiary oil recovery method employs indigenous microorganisms and their metabolic products to enhance oil mobilization. Although a significant amount of research has been undertaken on MEOR, the absence of convincing evidence has contributed to the petroleum industry’s low interest, as evidenced by the issuance of 400+ patents on MEOR that have not been accepted by this sector. The majority of the world’s MEOR field trials are briefly described in this review. However, the presented research fails to provide valid verification that the microbial system has the potential to address the identified constraints. Rather than promising certainty, MEOR will persist as an unverified concept unless further research and investigations are carried out.

The microbial enhanced oil recovery (MEOR) method is an eco-friendly and economical alternative technology. The technology involves a variety of uncertainties, and its success depends on controlling microbial growth and metabolism. Though a few numerical studies have been carried out to reduce the uncertainties, no attempt has been made to consider temperature, pressure, and salinity in an integrated manner. In this study, a new modeling method incorporating these environmental impacts was proposed, and MEOR analysis was performed. As a result, accurate modeling was possible to prevent overestimating the performance of MEOR. In addition, oil recovery was maximized through sensitivity analysis and optimization based on an integrative model. Finally, applying MEOR to an actual reservoir model showed a 7% increase in oil recovery compared to waterflooding. This result proved the practical applicability of the method.

Abstract A novel concept of microbial enhanced oil recovery (MEOR) under nonisothermal conditions was developed based on temperature-dependent biokinetics. The model specified the use of temperature-triggered Dextran (a biopolymer) produced by Leuconostoc mesenteroides (a microbe). The effects of environmental temperature on microbial growth and biopolymer production were validated and calibrated using the cardinal temperature model and experimental results. Various biokinetic parameters and a permeability reduction factor were also obtained to within approximately 2% error of those previously reported sandpack experiment. Based on the developed nonisothermal biokinetic model and the permeability reduction factor, thermally active MEOR was analyzed for a high-temperature reservoir. The results suggested the influences of injection parameters, such as injected nutrient concentration, rate, and temperature, on oil recovery factor. Higher nutrient concentrations resulted in increased Dextran production, thereby increasing oil recovery by selective plugging. On the other hand, injection rate and temperature were related to Dextran distributions. Higher injection rates led to lower Dextran concentrations with wider distributions. The injection temperature controlled the location of trapped Dextran in porous media, thereby influencing oil recovery. Through the optimization process, the injection design was determined with a rate of 30 m3∙day−1, temperature of 5 °C, and nutrient mole fraction of 0.009. The suggested optimal injection design resulted in the largest oil recovery (39%) for a highly heterogeneous layered reservoir. Highlights • Utilization of Leuconostoc mesenteroids for biokinetic modeling with experimental data with Dextran. • Validation of temperature effect on microbial growth comparing two analytical model. • Investigation of the reservoir and injection temperature effects on selective plugging mechanism of MEOR. • Sensitive analysis of injection design parameter such as injection nutrient concentration, rate, temperature. • Optimized injection design through the objective function to maximize oil recovery. [ABSTRACT FROM AUTHOR]

A facultative strain Luteimonas huabeiensis sp. nov. HB-2 isolated from Baolige Oilfield of China was examined for its growth, biosurfactant production, hydrocarbon degradation and the effects on interfacial properties of oil recovery system. Specifically, the effects on reduction of fluid surface tension and oil viscosity, and on increase in emulsification activity for crude oil were evaluated. This was attributed to the combination of the strain's activities including the production of biosurfactants (cyclic lipopeptides) and the degradation of crude oil. The produced biosurfactants can effectively reduce the interfacial tension of oil-water and viscosity of crude oil. Meanwhile, the long-chain hydrocarbons (C 20 -C 35 ) of crude oil also can be degraded by bacteria resulting in the increase in shorter chain (C 10 -C 19 ). These activities demonstrated the suitability of strain HB-2 for application in microbial enhanced oil recovery (MEOR). This was confirmed by a laboratory-based core column flooding evaluation, showing an average increase of 11% in oil recovery, which was followed by an oilfield test involving two water injection wells and eight oil production wells over 16 months, resulting in a remarkable increase in the average single well oil production from 0.48 ton/day (without MEOR) to 1.77 ton/day with the highest reaching 9.5 ton/day by MEOR. [ABSTRACT FROM AUTHOR]

Microbial enhanced oil recovery (MEOR) is a type of enhanced oil recovery (EOR) technology, generally employed as a tertiary stage where oil recovery using primary and secondary traditional methods is not feasible anymore. Amongst several potential biological agents useful for MEOR, biosurfactants (biologically produced amphiphilic surfactants) play key roles. They are mostly equivalent to or better than their chemical counterparts in several aspects including; better environmental compatibility, production from renewable waste substrates, maintaining activity at harsh environmental conditions, lower or no environmental toxicity. Biosurfactants are still not cost-competitive when compared to chemical surfactants. Different strategies like the use of cheaper raw materials, optimization of media components, fermentation processes and downstream processes, use of hyperproducers are currently explored to improve biosurfactant production economics. Biosurfactant mediated MEOR (BS-MEOR) could be applied by either in-situ or ex-situ techniques. In-situ BS-MEOR could be applied by injecting biosurfactant producing microorganisms in the oil well with or without additional nutrients. Generally followed by shut-in phase and subsequently monitoring microbial activities, metabolites production and oil recovery from the producer wells. Whereas for ex-situ BS-MEOR applications, the biosurfactant is produced outside the oil well and injected directly for enhancing oil recovery. This review highlights the biosurfactant production and economics, general protocols for applications from lab-to-field scale, different successful trials along with pros and cons of both in-situ and ex-situ BS-MEOR applications. [ABSTRACT FROM AUTHOR]

Microbial enhanced oil recovery (MEOR) applies biotechnology to improve residual crude oil production from substratum reservoir. MEOR includes in-situ MEOR and ex-situ MEOR. The former utilizes microbial growth and metabolism in the reservoir, and the latter directly injects desired active products produced by microbes on the surface. Taking biosurfactant-producing strainPseudomonas aeruginosaWJ-1 for research objects, in-situ enhanced oil recovery and ex-situ enhanced oil recovery by biosurfactant-producing strain WJ-1 were comparatively investigated in sand-pack columns.The results showed thatP.aeruginosaWJ-1 really proliferated in sand-pack columns, produced 2.66 g/L of biosurfactant, altered wettability, reduced oil-water interfacial tension (IFT) and emulsified crude oil under simulated in-situ process. Results also showed that higher biosurfactant concentration, lower IFT, smaller average diameters of emulsified crude oil were obtained in in-situ enhanced oil recovery experiment than those in ex-situ enhance oil recovery experiment. Similar wettability alteration was observed in both in-situ and ex-situ enhanced oil recovery experiment. The flooding experiments in sand-pack columns revealed that the recovery of in-situ was 7.46%/7.32% OOIP (original oil in place), and the recovery of the ex-situ was 4.64%/4.49% OOIP. Therefore, in-situ approach showed greater potential in enhancing oil recovery in contrast with ex-situ approach. It is recommended that the stimulation of indigenous microorganisms rather than injection of microbial produced active products should be applied when MEOR technologies were employed. [ABSTRACT FROM PUBLISHER]

This paper studies theGeobacillus stearothermophilusSL-1 that is widely distributed in oil reservoirs. We also carried out the emulsification stability experiment of paraffin. The particle size distributions of oil-emulsified droplets from the emulsified bacteria and their metabolites were determined by laser particle size analyzer. Using the glass model of the dimensional microscopic visualization, the oil displacement mechanism and effect of the emulsified bacteria on the remaining oil in the simulated reservoir environment were studied. The results show that the emulsified bacteria and their products can effectively emulsify the crude oil, and can form the large emulsion of a big viscosity with the crude oil during oil displacement, which is helpful to increase the flow resistance of the hyperosmotic channel, improve the ratio of oil to water, and enlarge the volume of the injected liquid. The microbial fermentation has a better effect to enhance the recovery than the metabolites or the microbial cell alone, and the oil recovery was enhanced by about 19%. This study has provided new insights and theoretical basis for microbial oil displacement. [ABSTRACT FROM AUTHOR]

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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]

This study used an exogenous lipopeptide-producing Bacillus subtilis to strengthen the indigenous microbial enhanced oil recovery (IMEOR) process in a water-flooded reservoir in the laboratory. The microbial processes and driving mechanisms were investigated in terms of the changes in oil properties and the interplay between the exogenous B. subtilis and indigenous microbial populations. The exogenous B. subtilis is a lipopeptide producer, with a short growth cycle and no oil-degrading ability. The B. subtilis facilitates the IMEOR process through improving oil emulsification and accelerating microbial growth with oil as the carbon source. Microbial community studies using quantitative PCR and high-throughput sequencing revealed that the exogenous B. subtilis could live together with reservoir microbial populations, and did not exert an observable inhibitory effect on the indigenous microbial populations during nutrient stimulation. Core-flooding tests showed that the combined exogenous and indigenous microbial flooding increased oil displacement efficiency by 16.71%, compared with 7.59% in the control where only nutrients were added, demonstrating the application potential in enhanced oil recovery in water-flooded reservoirs, in particular, for reservoirs where IMEOR treatment cannot effectively improve oil recovery. [ABSTRACT FROM AUTHOR]

A screening for biosurfactant-producing bacteria was conducted with 217 strains that were isolated from environmental samples contaminated with crude oil and/or petroleum derivatives. Although 19 promising biosurfactant producers were detected, strain TSBSO 3.8, which was identified by molecular methods as Bacillus amyloliquefaciens , drew attention for its production of a high-activity compound that presented an emulsification activity of 63% and considerably decreased surface (28.5 mN/m) and interfacial (11.4 mN/m) tensions in Trypticase Soy Broth culture medium. TSBSO 3.8 growth and biosurfactant production were tested under different physical and chemical conditions to evaluate its biotechnological potential. Biosurfactant production occurred between 0.5% and 7% NaCl, at pH values varying from 6 to 9 and temperatures ranging from 28 to 50°C. Moreover, biosurfactant properties remained the same after autoclaving at 121 °C for 15 min. The biosurfactant was also successful in a test to simulate microbial enhanced oil recovery (MEOR). Mass spectrometry analysis showed that the surface active compound was a surfactin, known as a powerful biosurfactant that is commonly produced by Bacillus species. The production of a high-efficiency biosurfactant, under some physical and chemical conditions that resemble those experienced in an oil production reservoir, such as high salinities and temperatures, makes TSBSO 3.8 an excellent candidate and creates good expectations for its application in MEOR. [ABSTRACT FROM AUTHOR]

Two indigenous bacterial consortia, IMP-100 and IMP-200, proved to have a functional effect on heavy crude oil recovery, indicating a potential implementation in Microbial Enhanced Oil Recovery (MEOR). Growth kinetics of the indigenous bacterial population was performed under anaerobic conditions at 70 °C and 33 g L −1 of salinity. It was found that both extremophile consortia were able to grow under the latter conditions. Moreover, they synthesized metabolites that altered the surface properties of the supernatants derived from cell cultures, a useful property in oil recovery processes. Ex situ fermentations in the presence of crude oil-impregnated calcite rocks demonstrated that both bacterial consortia enhance crude oil recovery by 8.5% and 13%. In order to identify possible phenomena responsible for incremental oil recovery, emulsification index ( E 24 ), surface tension, cell adhesion to hydrocarbons, and crude oil viscosity were characterized. The results demonstrate that IMP-(100, 200) consortia were able to recover heavy crude oil from calcite rocks, possibly due to a decrease in crude oil viscosity, induced by the presence of metabolites and/or the interaction between bacteria and oil hydrocarbons. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hyperthermophilic, alkalophilic, halophilic bacteria enriched from oil well. [•] Bacterial consortium enhanced oil recovery at 96°C in core flood studies. [•] 96°C is the highest temperature reported for Microbial Enhanced Oil Recovery. [•] Microbial metabolites aiding oil recovery at 96°C were identified. [ABSTRACT FROM AUTHOR]

Biostimulation of petroleum reservoir to improve oil recovery has been conducted in a large number of oilfields. However, the roles and linkages of organic nutrients, inorganic salts and oxygen content during biostimulation have not been effectively elucidated. Therefore, we investigated the relationships between carbon source, nitrogen source, phosphorus source, oxygen content, and microbial stimulation, oil emulsification, and oil degradation. The organic nutrients (molasses) accelerated microbial growth, and promoted oil emulsification under aerobic conditions. The added molasses also promoted metabolites production (CO, CH and acetic acid) and microbial anaerobic hydrocarbon degradation under anaerobic conditions. (NH)HPO improved gases production by neutralizing the acidic production and molasses. NaNO could also improve gases production by inhibiting sulfate-reducing bacteria to adjust pH value. Oxygen supply was necessary for oil emulsification, but bountiful supply of oxygen aggravated oil degradation, leading the entire ranges of alkanes and some aromatic hydrocarbons were degraded. Core-flooding experiments showed an oil displacement efficiency of 13.81 % in test with air package injected, 8.56 % without air package injection, and 4.77 % in control test with air package injection and 3.61 % without air package injection. The results suggest that the combined effect of organic nutrients, inorganic salts and oxygen content determines microbial growth, while production of metabolites, oil emulsification and biodegradation alter the reservoir biochemical characters and influence oil recovery during stimulation. [ABSTRACT FROM AUTHOR]

Enterobacter cloacae strain JD, which produces water-insoluble biopolymers at optimal temperature of 30 °C, and a thermophilic Geobacillus strain were used to construct an engineered strain for exopolysaccharide production at high temperatures by protoplast fusion. The obtained fusant strain ZR3 produced exopolysaccharides at up to 45 °C with optimal growth temperature at 35 °C. The fusant produced exopolysaccharides of approximately 7.5 g/L or more at pH between 7.0 and 9.0. The feasibility of the enhancement of crude oil recovery with the fusant was tested in a sand-packed column at 40 °C. The results demonstrated that bioaugmentation of the fusant was promising approach for MEOR. Mass growth of the fusant was confirmed in fermentor tests. [ABSTRACT FROM AUTHOR]

Microbial enhanced oil recovery (MEOR) refers to the process of using bacterial activities for more oil recovery from oil reservoirs mainly by interfacial tension reduction and wettability alteration mechanisms. Investigating the impact of these two mechanisms on enhanced oil recovery during MEOR process is the main objective of this work. Different analytical methods such as oil spreading and surface activity measurements were utilized to screen the biosurfactant-producing bacteria isolated from the brine of a specific oil reservoir located in the southwest of Iran. The isolates identified by 16S rDNA and biochemical analysis as Enterobacter cloacae (Persian Type Culture Collection (PTCC) 1798) and Enterobacter hormaechei (PTCC 1799) produce 1.53 g/l of biosurfactant. The produced biosurfactant caused substantial surface tension reduction of the growth medium and interfacial tension reduction between oil and brine to 31 and 3.2 mN/m from the original value of 72 and 29 mN/m, respectively. A novel set of core flooding tests, including in situ and ex situ scenarios, was designed to explore the potential of the isolated consortium as an agent for MEOR process. Besides, the individual effects of wettability alteration and IFT reduction on oil recovery efficiency by this process were investigated. The results show that the wettability alteration of the reservoir rock toward neutrally wet condition in the course of the adsorption of bacteria cells and biofilm formation are the dominant mechanisms on the improvement of oil recovery efficiency. [ABSTRACT FROM AUTHOR]

A considerable portion of oil reserves in Mexico corresponds to heavy oils. This feature makes it more difficult to recover the remaining oil in the reservoir after extraction with conventional techniques. Microbial enhanced oil recovery (MEOR) has been considered as a promising technique to further increase oil recovery, but its application has been developed mainly with light oils; therefore, more research is required for heavy oil. In this study, the recovery of Mexican heavy oil (11.1°API and viscosity 32,906 mPa s) in a coreflood experiment was evaluated using the extremophile mixed culture A7, which was isolated from a Mexican oil field. Culture A7 includes fermentative, thermophilic, and anaerobic microorganisms. The experiments included waterflooding and MEOR stages, and were carried out under reservoir conditions (70°C and 9.65 MPa). MEOR consisted of injections of nutrients and microorganisms followed by confinement periods. In the MEOR stages, the mixed culture A7 produced surface-active agents (surface tension reduction 27 mN m−1), solvents (ethanol, 1738 mg L−1), acids (693 mg L−1), and gases, and also degraded heavy hydrocarbon fractions in an extreme environment. The interactions of these metabolites with the oil, as well as the bioconversion of heavy oil fractions to lighter fractions (increased alkanes in the C8–C30 range), were the mechanisms responsible for the mobility and recovery of heavy oil from the porous media. Oil recovery by MEOR was 19.48% of the residual oil in the core after waterflooding. These results show that MEOR is a potential alternative to heavy oil recovery in Mexican oil fields. [ABSTRACT FROM AUTHOR]

Abstract: The success of biotechnological processes for oil recovery depends on adequate understanding of the system components: microorganisms, oil and porous media. Nine oil samples were collected from a carbonate oil reservoir in Cordoba Platform, Veracruz, Mexico. Geochemical characterisation demonstrated heavy oils with: API gravity of 10.7 to 14.5°, 3 to 5% sulphur, 36.58 to 54.06% aromatic hydrocarbons and −23.98 to −24.24 (‰) δ13C isotopic values in total oil. Additionally, the pristane/phytane ratio (Pr/Ph)<1 indicated an anoxic depositional environment. Results showed that native microbiota could have contributed to the biogeochemical transformation of the oil in the reservoir. Anaerobic, thermophilic, halotolerant and fermentative enrichment cultures were obtained from the nine oil samples (A1–A9). Metabolites such as CO2, CH4, ethanol, acetone, acetate and biosurfactants were detected. Mixed culture from the A7 sample showed the highest activity among all the mixed cultures screened, growing under 50 to 80°C, 5 to 35gL−1 NaCl and 0.8 to 14.2MPa pressure. Its kinetic parameters were μmax =0.321h−1 and Ks=0.54gL−1. These results were used to determine the conditions for oil recovery assays. A7 culture enhanced recovery of up to 12% of heavy oil (11.16°API) in oil impregnated carbonate granular porous media. Analysis of the V3 region of the 16S rRNA gene of the A7 culture showed that the predominant taxon was Thermoanaerobacter. Phylogenetic approximations demonstrated that similitude percentage of 99.9% corresponded to Thermoanaerobacter ethanolicus, 99.6% to Thermoanaerobacter pseudethanolicus and 98.9% to Thermoanaerobacter brockii and Thermoanaerobacter finii. [Copyright &y& Elsevier]

Abstract: A hydrocarbon-degrading strain, Rhodococcus ruber Z25, was isolated from the formation brine in Daqing Oilfield, China. The strain Z25 was able to grow under facultative anaerobic condition and produce biosurfactant while hydrocarbon was used as sole carbon source. The biosurfactant of R. ruber Z25 showed a perfect emulsification activity and was able to lower the interfacial tension to approximately 1.0mN/m and achieved a CMC value of 57mg/L. The biodegradation experiments of the crude oil by the strain Z25 under aerobic and anaerobic conditions exhibited positive effects in improving the physical properties of the crude oil, including mobility enhancement, cloud point reduction and wax degradation. Waterflooding experiments were done to investigate the MEOR potential of the strain and varied oil recovery efficiencies from 8.88% to 25.78% were achieved. The main MEOR mechanisms of the strain Z25 included hydrocarbon degradation, improvement of oil mobility, wettability alteration and selective plugging. These results revealed that strain Z25 exhibited a tremendous potential for MEOR application. [Copyright &y& Elsevier]

Abstract: Microbial enhanced oil recovery (MEOR) is a petroleum biotechnology for manipulating function and/or structure of microbial environments existing in oil reservoirs for prolonged exploitation of the largest source of energy. In this study, an Enterobacter cloacae which is capable of producing water-insoluble biopolymers at 37°C and a thermophilic Geobacillus strain were used to construct an engineered strain for exopolysaccharide production at higher temperature. The resultant transformants, GW3-3.0, could produce exopolysaccharide up to 8.83gl−1 in molasses medium at 54°C. This elevated temperature was within the same temperature range as that for many oil reservoirs. The transformants had stable genetic phenotype which was genetically fingerprinted by RAPD analysis. Core flooding experiments were carried out to ensure effective controlled profile for the simulation of oil recovery. The results have demonstrated that this approach has a promising application potential in MEOR. [Copyright &y& Elsevier]

The article presents a study which examines the use of crude oil in Streptococcus sp. BT-003 cultivation in order for it to produce organic acid, bio-gas and polysaccharide. It mentions that the use of crude oil has reduced the viscosity of crude oil from 8000-15000 mPa.s to 50-250 mPa.s. It has also increased the content of organic acid from 8-15 times and reduced the content of paraffin and resin from 60-95%. In addition, the interfacial tension between water and crude oil was also reduced.

A field experiment was performed to monitor changes in exogenous bacteria and to investigate the diversity of indigenous bacteria during a field trial of microbial enhanced oil recovery (MEOR). Two wells (26–195 and 27–221) were injected with three exogenous strains and then closed to allow for microbial growth and metabolism. After a waiting period, the pumps were restarted and the samples were collected. The bacterial populations of these samples were analyzed by denaturing gradient gel electrophoresis (DGGE) with PCR-amplified 16S rRNA fragments. DGGE profiles indicated that the exogenous strains were retrieved in the production water samples and indigenous strains could also be detected. After the pumps were restarted, average oil yield increased to 1.58 and 4.52 tons per day in wells 26–195 and 27–221, respectively, compared with almost no oil output before the injection of exogenous bacteria. Exogenous bacteria and indigenous bacteria contributed together to the increased oil output. Sequence analysis of the DGGE bands revealed that Proteobacteria were a major component of the predominant bacteria in both wells. Changes in the bacteria population in the reservoirs during MEOR process were monitored by molecular analysis of the 16S rRNA gene sequence. DGGE analysis was a successful approach to investigate the changes in microorganisms used for enhancing oil recovery. The feasibility of MEOR technology in the petroleum industry was also demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: These experiments aim to investigate the microbial enhanced oil recovery (MEOR) technique in fractured porous media using etched-glass micromodels. Three identically patterned micromodels with different fracture angle orientation of inclined, vertical and horizontal with respect to the flow direction were utilized. A non-fractured model was also used to compare the efficiency of MEOR in fractured and non-fractured porous media. Two types of bacteria were employed: Bacillus subtilis (a biosurfactant-producing bacterium) and Leuconostoc mesenteroides (an exopolymer-producing bacterium). The results show that higher oil recovery efficiency can be achieved by using biosurfactant-producing bacterium in fractured porous media. Further investigation on the effect of the mentioned bacteria on oil viscosity, porous media permeability and wettability suggests that the plugging of matrix-fracture interfaces by an exopolymer is the main reason for the low performance of the exopolymer-producing bacterium. Oil viscosity reduction as well as the reduction of IFT was also found to be the reason for better microbial recovery efficiencies of biosurfactant-producing bacterium in the fractured models. [Copyright &y& Elsevier]

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]

Green enhanced oil recovery (GEOR) is an eco-friendly EOR technique involving the injection of specific green fluids to improve macroscopic and microscopic sweep efficiencies, boosting residual oil production. The environmentally friendly surfactant-polymer (SP) flood is successfully tested in a sandstone reservoir. However, the applicability of the SP method does not extend to carbonate reservoirs yet and requires comprehensive investigation. This work aims to explore the oil recovery competency of a green SP formulation in carbonate through experimental and modelling studies. Numerous formulations of SP with ketone, alcohol, and organic acid are selected based on phase behavior and interfacial tension (IFT) reduction capabilities to examine their potential for enhancing residual oil production from carbonate cores. A blending of nonionic green surfactant alkyl polyglucoside (APG), xanthan gum (XG) biopolymer, and butanone recovered 22% tertiary oil from the carbonate core. This formulation recovered more than double residual crude than that of the APG, XG, and acetone. Similarly, a combination of APG, XG, acrylic acid, and butanol increased significantly more oil than the APG, XG, and acrylic acid formulation. The APG, XG, and butanone mixture is efficient with regards to boosting tertiary oil recovery from the carbonate core. [ABSTRACT FROM AUTHOR]