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Environmental protection requirements and the need to increase the proportion of oil recovered by secondary methods have led to the rise in popularity of microbial enhanced oil recovery (MEOR) techniques. Usually, MEOR requires the use of indigenous strains of microorganisms residing in wells, as they are adapted to local conditions. However, for some wells and fields, such as the Boca de Jaruco field in Cuba, information about the oilfield microorganisms and their properties is extremely limited. One of the properties crucial for the successful implementation of MEOR in fields is the ability of indigenous strains to produce biosurfactants. The aim of the present study is to evaluate the ability of six bacterial isolates obtained from the Boca de Jaruco field in Cuba to produce biosurfactants. The isolates capable of utilizing oil as their sole carbon source were identified as Bacillus subtilis (strains CC21, CC23, CC31, and CC32), Bacillus licheniformis (strain CC33), and Aeromonas veronii (strain CC22). It was determined that all isolates can tolerate temperatures between 30 and 60 °C, salinity ranging from 0.5 to 10.0% NaCl, and pH levels between 6 and 9. Regarding their ability to produce biosurfactants, assessed using the drop collapse method, oil-spreading method, emulsification activity test, and surface tension measurement, the isolates ranked as follows: A. veronii CC22 > B. subtilis CC21 = B. subtilis CC31 > B. subtilis CC23 = B. subtilis CC32 > B. licheniformis CC33. The biosurfactants produced were stable in the presence of 1.7 to 20.0% NaCl, irrespective of temperature (30 or 70 °C). However, substituting 20% of the NaCl with CaCl2 resulted in destabilization of the biosurfactants produced by all investigated isolates, with destabilization levels averaging up to 32% at 70 °C. [ABSTRACT FROM AUTHOR]

Rhamnolipids are a class of anionic glycolipid surfactants produced through microbial metabolism. As a widely researched biosurfactant, rhamnolipids possess several advantages over traditional chemical surfactants, including non-toxicity, eco-friendliness, biodegradability, and biocompatibility, particularly in the context of microbial oil recovery applications. This class of surfactants enhances oil recovery by reducing the interfacial tension between oil and water, emulsifying residual oil, and modifying the wettability of rock surfaces. Furthermore, rhamnolipids maintain stability in high-temperature and high-salinity environments. However, rhamnolipids derived from different fermentation substrates exhibit variations in structure, composition, and properties, resulting in distinct displacement effects and mechanisms of action. This study focuses on two types of rhamnolipids: typical rhamnolipid and high-yield rhamnolipid, which are fermented using glycerol and rapeseed oil, respectively. Based on the characteristics of the target heavy oil reservoir, micromodels were designed and manufactured to conduct microfluidic experiments. The results obtained from imaging and video recording were analyzed qualitatively and quantitatively to explore the differences in effects and mechanisms between the two rhamnolipid systems. Results indicate that typical rhamnolipid increased recovery by 4.41% through delayed mechanisms involving wettability modification and residual oil emulsification. Conversely, high-yield rhamnolipid demonstrates an immediate effect by reducing interfacial tension, resulting in a recovery increase in 5.68%. According to the observed experimental phenomena and analytical trends, the conclusions evaluate the production increase, clarify the differences in mechanisms of action, and enhance the microscopic understanding of these surfactants. These findings provide directions for future investigations and serve as a reference for the design of related schemes. [ABSTRACT FROM AUTHOR]

Microbial enhanced oil recovery (MEOR) is a promising technology for oil field extraction. This study investigated a co-culture system of Pseudomonas aeruginosa and Bacillus subtilis to increase MEOR efficacy. We analyzed bacterial growth, biosurfactant production, and crude oil emulsified performance under different inoculation ratios. Compared to single cultures, the co-culture system showed superior growth and functional expression, with an optimal inoculation ratio of 1:1. Quantitative assessments of the cell numbers and biosurfactant production during the co-culture revealed that rapid B. subtilis proliferation in early stages significantly stimulated P. aeruginosa growth. This interaction increased cell density and rhamnolipid production by 208.05% and 216.25%, respectively. The microscopic etching model displacement results demonstrated enhanced emulsification and mobilization of crude oil by the co-culture system, resulting in 94.48% recovery. A successful field application in a block-scale reservoir increased cumulative oil production by 3.25 × 103 t. An analysis of microbial community structure and function in different phases revealed that after co-culture system injection, Pseudomonas became the dominant genus in the reservoir community, with an average abundance of 24.80%. Additionally, the abundance of biosurfactant-producing and hydrocarbon-degrading bacteria increased significantly. This research and the application of the P. aeruginosa and B. subtilis co-culture system provide novel insights and strategies for MEOR. [ABSTRACT FROM AUTHOR]

Biosurfactants produced by bacteria possess remarkable emulsification properties for crude oil, significantly enhancing oil mobility and recovery rates. This study aimed to isolate and screen biosurfactant-producing bacteria for oil enhancing recovery. A total of 93 bacterial strains were isolated from marine sediments, with three high-yield biosurfactant-producing strains identified: Pseudomonas aeruginosa N33, Bacillus paralicheniformis Nian2, and Stenotrophomonas nematodicola T10. The fermentation conditions, such as pH, carbon source, nitrogen source, and C/N ratio, were optimized to maximize the yield and activity of biosurfactants. Further evaluations were performed to assess the stability of the bio-surfactant activity and its emulsification properties. The results indicated that all three strains produced biosurfactants that retained their oil displacement activity in the presence of Na+ and Mg2+, but showed a significant reduction in their activities in the presence of Ca2+. The biosurfactants maintained their original activity after treatment at 120 °C for 3 h. Additionally, the biosurfactants produced by all three strains demonstrated excellent oil emulsification capabilities. Static oil-washing and dynamic displacement experiments revealed static oil recovery rates of 28.1%, 23.4%, and 7.1%, respectively, for N33, Nian2, and T10, and dynamic oil displacement recovery rates of 95.0%, 74.1%, and 69.0%, respectively. This research provides valuable microbial resources for enhancing oil recovery via microorganisms and lays a foundation for practical application. [ABSTRACT FROM AUTHOR]

The exploitation of nature and the increase in manufacturing production are the cause of major environmental concerns, and considerable efforts are needed to resolve such issues. Oil and petroleum derivatives constitute the primary energy sources used in industries. However, the transportation and use of these products have huge environmental impacts. A significant issue with oil-related pollution is that hydrocarbons are highly toxic and have low biodegradability, posing a risk to ecosystems and biodiversity. Thus, there has been growing interest in the use of renewable compounds from natural sources. Biosurfactants are amphipathic microbial biomolecules emerging as sustainable alternatives with beneficial characteristics, including biodegradability and low toxicity. Biosurfactants and biosurfactant-producing microorganisms serve as an ecologically correct bioremediation strategy for ecosystems polluted by hydrocarbons. Moreover, synthetic surfactants can constitute additional recalcitrant contaminants introduced into the environment, leading to undesirable outcomes. The replacement of synthetic surfactants with biosurfactants can help solve such problems. Thus, there has been growing interest in the use of biosurfactants in a broad gamut of industrial sectors. The purpose of this review was to furnish a comprehensive view of biosurfactants, classifications, properties, and applications in the environmental and energy fields. In particular, practical applications of biosurfactants in environmental remediation are discussed, with special focus on bioremediation, removal of heavy metals, phytoremediation, microbial enhanced oil recovery, metal corrosion inhibition, and improvements in agriculture. The review also describes innovating decontamination methods, including nanobioremediation, use of genetically modified microorganisms, enzymatic bioremediation, modeling and prototyping, biotechnology, and process engineering. Research patents and market prospects are also discussed to illustrate trends in environmental and industrial applications of biosurfactants. [ABSTRACT FROM AUTHOR]

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]

With oilfields enter the late stage of development, which is difficult to extract residual oil in the reservoirs. Microbial oil displacement is favored as an efficient and clean stimulation method. As an important mechanism of the technology, biosurfactants are being studied and applied. Differ from traditional synthetic surfactants, biosurfactants are more practical, economically valuable and environmentally friendly. This article describes the three action mechanisms of biosurfactants and introduces the current research status and technological achievements of glycolipids, lipopeptides, fatty acids, polymers, and phospholipids. Compare the advantages and limitations of each the above, introduce the field application method and effect, and prospect the future development direction of this technology and provide reasonable suggestions. The results show that biosurfactants have obvious advantages, which can change oil water interfacial tension, emulsify crude oil, and achieve wetting reversal, improving crude oil recovery rate. It has enormous development potential in oilfield production, further on-site testing is needed for technology in the future. It is necessary to enhance its compatibility in different types of formations, especially to achieve good results in special reservoirs. By controlling the oil displacement cost, it can achieve the goal of reducing costs, increasing efficiency, and further improving crude oil recovery. [ABSTRACT FROM AUTHOR]

Abstract Microbial enhanced oil recovery (MEOR) is a cost effective and efficient method for recovering residual oil. However, the presence of wax (paraffin) in residual oil can substantially reduce the efficiency of MEOR. Therefore, microbial dewaxing is a critical process in MEOR. In this study, a bacterial dewaxing agent of three spore-forming bacteria was developed. Among these bacteria, Bacillus subtilis GZ6 produced the biosurfactant surfactin. Replacing the promoter of the surfactin synthase gene cluster (srfA), increased the titer of surfactin in this strain from 0.33 g/L to 2.32 g/L. The genetically modified strain produced oil spreading rings with diameters increasing from 3.5 ± 0.1 to 4.1 ± 0.2 cm. The LadA F10L/N133R mutant was created by engineering an alkane monooxygenase (LadA) using site-directed mutagenesis in the Escherichia coli host. Compared to the wild-type enzyme, the resulting mutant exhibited an 11.7-fold increase in catalytic efficiency toward the substrate octadecane. When the mutant (pIMPpladA2mu) was expressed in Geobacillus stearothermophilus GZ178 cells, it exhibited a 2.0-fold increase in octadecane-degrading activity. Cultures of the two modified strains (B. subtilis GZ6 (pg3srfA) and G. stearothermophilus GZ178 (pIMPpladA2mu)) were mixed with the culture of Geobacillus thermodenitrificans GZ156 at a ratio of 5:80:15. The resulting composition increased the rate of wax removal by 35% compared to the composition composed of three native strains. This study successfully developed a multi-strain bacterial agent with enhanced oil wax removal capabilities by genetically engineering two bacterial strains.

Microbial enhanced oil recovery (MEOR) is a promising method for improving oil recovery from challenging reservoirs such as those found in Kazakhstan. MEOR relies on the activities of microorganisms to modify the properties of the reservoir, such as reducing the oil viscosity, increasing the reservoir permeability, and generating by-products that mobilize the oil. Implementing MEOR in Kazakhstan could lead to significant economic benefits for the country by increasing oil production and royalties from fossil fuel exports. Oil production in Kazakhstan has seen fluctuations in recent years, with 2018 recording a production level of 1.814 million barrels per day. Among regions, Atyrau region contributed the most to oil production with 23.4 million tons of oil. Following Atyrau, the Mangystau region produced 8.2 million tons, and Aktobe produced 2.4 million tons. Overall, the use of MEOR in Kazakhstan's oil fields could offer a promising solution for enhanced oil recovery, while minimizing environmental impact and cost. While specific data on the current use of MEOR in field conditions in Kazakhstan might be limited, the fact that studies are underway suggests a growing interest in applying this technology in the country's oil fields. It is exciting to think about the potential benefits these studies could bring to Kazakhstan's oil industry once their findings are implemented in field operations. These studies have significant implications for Kazakhstan's oil production in the future. [ABSTRACT FROM AUTHOR]

Indigenous microbial enhanced oil recovery (IMEOR) is a promising alternative way to promote oil recovery. It activates oil recovery microorganisms in the reservoir by adding nutrients to the injected water, utilizing microbial growth and metabolism to enhance recovery. However, few studies have focused on the impact of injected nutrients on reservoir microbial community composition and potential functions. This limits the further strategic development of IMEOR. In this study, we investigated the effects of nutrition on the composition of the reservoir bacterial community and functions in the Qizhong block of Xinjiang Oilfield, China, by constructing a long core microbial flooding simulation device. The results showed that the microbial community structure of the reservoir changed from aerobic state to anaerobic state after nutrient injection. Reducing the nutrient concentration increased the diversity and network stability of the reservoir bacterial community. At the same time, the nitrogen metabolism function also showed the same change response. Overall, these results indicated that nutrition significantly affected the community structure and function of reservoir microorganisms. Injecting low concentrations of nutrients may be more beneficial to improve oil recovery. This study is of great significance for guiding IMEOR technology and saving costs at the field site. [ABSTRACT FROM AUTHOR]

Microbial enhanced oil recovery (MEOR) is a cost effective and efficient method for recovering residual oil. However, the presence of wax (paraffin) in residual oil can substantially reduce the efficiency of MEOR. Therefore, microbial dewaxing is a critical process in MEOR. In this study, a bacterial dewaxing agent of three spore-forming bacteria was developed. Among these bacteria, Bacillus subtilis GZ6 produced the biosurfactant surfactin. Replacing the promoter of the surfactin synthase gene cluster (srfA), increased the titer of surfactin in this strain from 0.33 g/L to 2.32 g/L. The genetically modified strain produced oil spreading rings with diameters increasing from 3.5 ± 0.1 to 4.1 ± 0.2 cm. The LadA F10L/N133R mutant was created by engineering an alkane monooxygenase (LadA) using site-directed mutagenesis in the Escherichia coli host. Compared to the wild-type enzyme, the resulting mutant exhibited an 11.7-fold increase in catalytic efficiency toward the substrate octadecane. When the mutant (pIMPpladA2mu) was expressed in Geobacillus stearothermophilus GZ178 cells, it exhibited a 2.0-fold increase in octadecane-degrading activity. Cultures of the two modified strains (B. subtilis GZ6 (pg3srfA) and G. stearothermophilus GZ178 (pIMPpladA2mu)) were mixed with the culture of Geobacillus thermodenitrificans GZ156 at a ratio of 5:80:15. The resulting composition increased the rate of wax removal by 35% compared to the composition composed of three native strains. This study successfully developed a multi-strain bacterial agent with enhanced oil wax removal capabilities by genetically engineering two bacterial strains. [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 cost-effective and eco-friendly for oil exploitation. Genetically modified biosurfactants-producing high-yield strains are promising for ex-situ MEOR. However, can they survive and produce biosurfactants in petroleum reservoirs for in-situ MEOR? What is their effect on the native bacterial community? Methods and results A genetically modified indigenous biosurfactants-producing strain Pseudomonas aeruginosa PrhlAB was bioaugmented in simulated reservoir environments. Pseudomonas aeruginosa PrhlAB could stably colonize in simulated reservoirs. Biosurfactants (200 mg l−1) were produced in simulated reservoirs after bio-augmenting strain PrhlAB. The surface tension of fluid was reduced to 32.1 mN m−1. Crude oil was emulsified with an emulsification index of 60.1%. Bio-augmenting strain PrhlAB stimulated the MEOR-related microbial activities. Hydrocarbon-degrading bacteria and biosurfactants-producing bacteria were activated, while the hydrogen sulfide-producing bacteria were inhibited. Bio-augmenting P. aeruginosa PrhlAB reduced the diversity of bacterial community, and gradually simplified the species composition. Bacteria with oil displacement potential became dominant genera, such as Shewanella, Pseudomonas , and Arcobacter. Conclusions Culture-based and sequence-based analyses reveal that genetically modified biosurfactants-producing strain P. aeruginosa PrhlAB are promising for in-situ MEOR as well. [ABSTRACT FROM AUTHOR]

Bio‐enhanced oil recovery (BEOR) is an advanced and innovative approach in the oil industry that could be a potential solution to increase oil production from existing reservoirs using technologies based on biological methods. Nevertheless, there has been a lack of comprehensive reviews that elucidate the various aspects and potential of different BEOR methods and processes. This review summarizes the recent progress of various methods employed in BEOR, exploring their applications and highlighting their distinct advantages. BEOR employs different techniques, including microorganisms and biomicrobes microbial enhanced oil recovery (MEOR), enzymes, biopolymers, bionanomaterials, alkaline, and biosurfactants to increase oil recovery. Microorganisms contribute significantly to BEOR through metabolic processes that result in the production of gases and acids. The role of enzymes is to enhance the fluid flow and thereby facilitate oil production. Biosurfactants reduce the interfacial tension (IFT) between oil and water and mobilize the trapped oil. Biopolymers are obtained from biological sources such as plants, microorganisms, and algae. Biopolymers can interact with oil, which is well‐used in the process of EOR. Bionano processes represent a fusion of biology and nanotechnology, integrate the advantages of both microorganisms and nanoparticles, and provide a synergic effect for EOR. The BEOR revealed an attractive potential to be an effective approach to maximizing the oil recovery considering environmental, economic productivity, and sustainability issues. Also, this review encourages further studies and development in this field for fully exploiting BEOR's capacity and meeting the ever‐increasing needs of energy resources with a sustainable viewpoint. [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue of the journal Processes that explores advancements in unconventional oil and gas recovery. Unconventional reservoirs, such as tight gas/oil reservoirs, shale gas/oil reservoirs, and coalbed methane, are examined due to their unique characteristics and their role in meeting global energy demands. The issue includes research and reviews on topics such as reservoir characterization, fluids in porous media, productivity evaluation, enhanced oil/gas recovery, and machine learning and data science applications. The studies presented offer new insights into the dynamics of unconventional reservoirs and propose innovative solutions to the challenges they present. The research is multidisciplinary and utilizes advanced laboratory tests and computational tools, aiming to provide valuable insights and practical solutions for industry professionals and researchers in the field of unconventional oil and gas recovery. [Extracted from the article]

The microbial communities associated with alkaline–surfactant–polymer (ASP)-flooded reservoirs have rarely been investigated. In this study, high-throughput sequencing was used to analyse the indigenous microbial communities in two different blocks, the water flooding after the alkaline–surfactant–polymer flooding block and the alkaline–surfactant–polymer flooding block, and to ascertain the optimal stage for the implementation of indigenous microbial oil recovery technology. The different displacement blocks had significant effects on the indigenous microbial community at the genus level according to an alpha diversity analysis and community composition. In water flooding after alkaline–surfactant–polymer flooding, the dominant genus of Pseudomonas exceeded 30%, increasing to 52.1% in alkaline–surfactant–polymer flooding, but alpha diversity decreased. Through a co-occurrence network analysis, it was found that the complexity of the water flooding after alkaline–surfactant–polymer flooding was higher than that of alkaline–surfactant–polymer flooding. This means that the water flooding ecosystem after alkaline–surfactant–polymer flooding was more stable and less susceptible to external environmental influences. In addition, there were significant differences in the functional redundancy of microbial communities in different blocks. In summary, the optimal stage for implementing local microbial oil recovery technology may be water flooding after alkaline–surfactant–polymer flooding. [ABSTRACT FROM AUTHOR]

The formation of hydrogen sulfide (H2S) in petroleum reservoirs by anaerobic microbial activity (through sulfate-reducing microorganisms, SRMs) is called biogenic souring of reservoirs and poses a risk in the petroleum industry as the compound is extremely toxic, flammable, and corrosive, causing devastating damage to reservoirs and associated surface facilities. In this paper, we present a workflow and the tools to assess biogenic souring from a pragmatic engineering perspective. The retention of H2S in the reservoir due to the reactions with iron-bearing rock minerals (e.g., siderite) is shown in a theoretical approach here and supported with literature data. Cases are provided for two fields under secondary (waterflooding) and tertiary flooding with microbial enhanced oil recovery (MEOR). The use of the Monte Carlo method as a numerical modeling tool to incorporate uncertainties in the measured physical/chemical/biochemical data is demonstrated as well. A list of studies conducted with different chemicals alone or in combination with various biocides to mitigate biogenic souring provides an overview of potential inhibitors as well as possible applications. Furthermore, the results of static and dynamic inhibition tests using molybdate are presented in more detail due to its promising mitigation ability. Finally, a three-step workflow for the risk assessment of biogenic souring and its possible mitigation is presented and discussed. [ABSTRACT FROM AUTHOR]

The editorial discusses the challenges posed by hydrophobic organic pollutants, such as hydrocarbons and microplastics, to the environment and human health. Physicochemical methods have been used to remove these pollutants, but they often result in toxic byproducts. Biosurfactants, eco-friendly surface-active molecules produced by microorganisms, offer a sustainable alternative for bioremediation. The editorial highlights the effectiveness of biosurfactants in enhancing the biodegradation of organic pollutants and emphasizes the need for further research to improve biosurfactant screening and production for large-scale environmental applications. [Extracted from the article]

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Microbial enhanced oil recovery (MEOR) is a promising method for improving oil recovery from challenging reservoirs such as those found in Kazakhstan. MEOR relies on the activities of microorganisms to modify the properties of the reservoir, such as reducing the oil viscosity, increasing the reservoir permeability, and generating by-products that mobilize the oil. Implementing MEOR in Kazakhstan could lead to significant economic benefits for the country by increasing oil production and royalties from fossil fuel exports. Oil production in Kazakhstan has seen fluctuations in recent years, with 2018 recording a production level of 1.814 million barrels per day. Among regions, Atyrau region contributed the most to oil production with 23.4 million tons of oil. Following Atyrau, the Mangystau region produced 8.2 million tons, and Aktobe produced 2.4 million tons. Overall, the use of MEOR in Kazakhstan’s oil fields could offer a promising solution for enhanced oil recovery, while minimizing environmental impact and cost. While specific data on the current use of MEOR in field conditions in Kazakhstan might be limited, the fact that studies are underway suggests a growing interest in applying this technology in the country’s oil fields. It is exciting to think about the potential benefits these studies could bring to Kazakhstan’s oil industry once their findings are implemented in field operations. These studies have significant implications for Kazakhstan’s oil production in the future.

The application of Microbial Enhanced Oil Recovery relies heavily on the microorganisms in oil wells. However, due to the difficulties in separating bacteria from oil samples, studies on bacterial communities in oil samples are limited. In this study, oil and produced water samples from the same well were collected from the western oilfield of the Ordos Basin, and DNA extraction was effective. Full-length 16S rRNA genes were sequenced using PacBio to study the impact of water flooding on the microbial community structure and the potential biochemical functions of bacteria in a low-permeability reservoir. The results showed that water flooding decreased the temperature and salinity while increasing the dissolved oxygen in the tested oil well. It has influence on the reservoir community. Nitrate-reducing bacteria such as Bradyrhizobium and Methylovirgula are enriched in the reservoir. Nitrate and nitrite can be used as electron acceptors by denitrification to produce N2, which can inhibit the growth of sulfate-reducing bacteria. Additionally, bacteria strains such as Flexistipes and Marinobacter can use hydrocarbons as energy source to degrade crude oil and change its properties. The study demonstrated the presence of a large number of advantageous bacteria in low-permeability reservoirs after water flooding, providing a biological foundation for the application of microbial enhanced oil recovery.

Microbial enhanced oil recovery (MEOR) is a promising technology for oil field extraction. This study investigated a co-culture system of Pseudomonas aeruginosa and Bacillus subtilis to increase MEOR efficacy. We analyzed bacterial growth, biosurfactant production, and crude oil emulsified performance under different inoculation ratios. Compared to single cultures, the co-culture system showed superior growth and functional expression, with an optimal inoculation ratio of 1:1. Quantitative assessments of the cell numbers and biosurfactant production during the co-culture revealed that rapid B. subtilis proliferation in early stages significantly stimulated P. aeruginosa growth. This interaction increased cell density and rhamnolipid production by 208.05% and 216.25%, respectively. The microscopic etching model displacement results demonstrated enhanced emulsification and mobilization of crude oil by the co-culture system, resulting in 94.48% recovery. A successful field application in a block-scale reservoir increased cumulative oil production by 3.25 × 103 t. An analysis of microbial community structure and function in different phases revealed that after co-culture system injection, Pseudomonas became the dominant genus in the reservoir community, with an average abundance of 24.80%. Additionally, the abundance of biosurfactant-producing and hydrocarbon-degrading bacteria increased significantly. This research and the application of the P. aeruginosa and B. subtilis co-culture system provide novel insights and strategies for MEOR.

In response to the problems of reduced formation pressure, insufficient reservoir energy, and serious water flooding of oil wells in the southern part of Block 6 of Chunfeng Oilfield (Xinjiang, China) due to high cycles of steam stimulation, based on the geological conditions and reasons for high water cut in the block, nitrogen foam profile control and microbial oil recovery technology were proposed. A comprehensive treatment technology for high water content wells with microbial technology as the main focus and plugging and adjustment technology as the auxiliary was formed. The actual application effect of this technology was tested. The resistance factor and residual resistance factor of nitrogen foam were 540 and 270, respectively, which were higher than those of contrast foam. The core pressure value was greater than that of the contrast foam with good plugging property. By using this technology, the water content of the oil wells in the southern block of the rear row decreased and the oil production increased with a maximum oil increase of 847 ton. Microbial oil recovery experiments found that microbial strains could reduce the viscosity with the maximum decrease of 78.3%. The cumulative total oil production after expanding the experimental wells of microbial oil recovery technology was 3,286 ton. To sum up, the nitrogen foam profile control and microbial oil recovery technologies proposed in the study could effectively improve the recovery efficiency in super heavy oil reservoirs in southern Pai 6 block. The innovation of the research was the combination of nitrogen foam profile control and microbial oil recovery technology, which enriched the current research on the treatment of high water cut wells in super heavy oil reservoirs and provided new ideas and technical guidance for the treatment of high water cut wells in super heavy oil reservoirs. It had positive significance in improving the recovery of high water cut wells in super heavy oil reservoirs. [ABSTRACT FROM AUTHOR]

The adsorption of asphaltene on the rock surface and the changes in its wettability are very relevant issues in flow assurance and oil recovery studies, and for carbonate reservoirs, they are even more important. During microbial enhanced oil recovery (MEOR) processes, wettability alteration is considered a crucial mechanism leading to improved oil recovery. Therefore, it is essential to understand the mechanisms of surface wettability changes by bacteria and biosurfactants and find new and reliable methods to prevent asphaltene adsorption. Hence, the main aim of this research was to investigate the effect of a mixture of thiobacillus thiooxidans and thiobacillus ferooxidans microorganisms with an optimum effective temperature of around 30 °C (referred to as mesophilic bacteria), as well as a mixture of two moderate thermophiles Sulfobacillus thermosulfidooxidans for operating temperatures around 50 °C (referred to as moderately thermophilic bacteria) on the adsorption of asphaltene samples isolated from two different crude oils onto main reservoir minerals (i.e., quartz and dolomite). The results indicated that after two weeks of mineral aging in moderate thermophilic bacteria, the adsorption of asphaltene on both minerals increased between 180 and 290%. Fourier-transform infrared spectroscopy (FTIR) analysis for quartz and dolomite samples demonstrated that after aging in bacterial solution, bonds related to the adsorption of bacterial cells and biosurfactant production appear, which are the main factors of change in wettability. Alteration in wettability towards hydrophilicity expands hydrogen bonds on the surface, thus improving asphaltene adsorption due to polar interaction. Asphaltene 1 changed the contact angle of dolomite from 53.85° to 90.51° and asphaltene 2 from 53.85° to 100.41°. However, both strains of bacteria caused a strong water-wetting effect on the dolomite rock samples. The influence of moderate thermophilic bacteria on surface wettability is more significant than that of mesophilic bacteria, which may be caused by the high protein content of these bacteria, which expands hydrogen bonding with the surface. Adsorption of asphaltenes on dolomite rocks previously aged with bacteria showed that the wetted rock samples retained their water-wet state. This study highlights the dual impact of the used microorganisms. On one hand, they significantly reduce contact angles and shift wettability towards a strongly water-wet condition, a crucial positive factor for MEOR. On the other hand, these microorganisms can elevate the adsorption of asphaltenes on reservoir rock minerals, posing a potential challenge in the form of formation damage, particularly in low-permeability reservoirs. [ABSTRACT FROM AUTHOR]

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]

Primary oil recovery is the first stage of hydrocarbon production in which a reservoir uses its natural energy to force hydrocarbon to its wellbore. Secondary oil recovery comes to play when hydrocarbons can no longer be further produced by natural means. The purpose of secondary recovery is to maintain reservoir pressure so as to displace hydrocarbons toward the wellbore. Both primary and secondary recovery processes cannot displace more than 50% of the available hydrocarbons in a reservoir. The remaining hydrocarbons are further recovered through Tertiary/Enhanced Oil Recovery techniques. According to literature, microbial enhanced oil recovery has been identified as a tertiary method used to improve the efficiency of hydrocarbon production from reservoirs. Microbial enhanced oil recovery is a feasible reservoir technology, which has not been widely used in the oil and gas industry owing to the attainment of the requisite reservoir conditions such as temperature within which microbes can thrive. Literature has shown that thermotolerant microbes can withstand optimum temperatures of 50–90°C, while deep and ultra-deep hydrocarbon reservoir temperatures are often above 100°C. This study identifies some isolated thermotolerant microbes from a sandstone reservoir that can withstand temperatures as high as 110°C via conventional methods and molecular analysis. The identified thermotolerant petroleum microbes: Bacillus amyloliquefaciens (A) and Bacillus nealsonii (B) were used to enhance oil recovery from a reservoir. The results showed that the microbial species A and B at a confined pressure of 3.0 MPa and temperature of 27°C, gave 46.4% and 48.6% oil recoveries, respectively, which is comparably higher than the value (26.9%) obtained for the water flooded samples. At temperatures of 80, 90, 100, 110 and 120°C, the oil recovery results show that the recovery factor (55.2%–64.1%) of species B were higher compared to the range (46.7–57.5%) recorded for species A. At the onset of the core flooding experiments, there was an initial increment in oil recovery factor as the temperature increased from 80 to 110°C, whereas, it remained constant within 110–120°C. This trend coincides with the drop in the thermal resistance exhibited by the microbes when exposed to such conditions. The cumulative oil production from the commercial Eclipse simulation closely matched those of the experiment results, whereas, the slight difference can be attributed to the adjustment of the simulation input parameters. The experimental results show that species B can be used to enhance oil recovery at reservoir temperature conditions above 100°C.

Performance evaluation of microorganisms that have emulsifying and degrading effects on crude oil has been extensively conducted in the laboratory. However, the ultimate goal of microbial enhanced oil recovery is field application, so the pilot simulation experiments are crucial. In this study, a micro-visualization model and the real cores were chosen to investigate the actual recovery efficiency and the mechanism of the consortium bacteria B-ALL, which has been proven to have good emulsification and degradation effects in lab studies in porous media. At the same time, the cast thin sections and rate-controlled porosimetry were combined to analyze the pore throat structure of the displacement core. It was found that the recovery efficiency was positively correlated with the microbial injection volume as well as the incubation time. For the microscopic model with high pores and high permeability, the efficiency of secondary water flooding can be increased by 44.77% after six days of incubation with two pore volume microbes. For the real tight cores, the maximum secondary water flooding efficiency under the same condition was 6.98%. Through visual modeling, microorganisms increase the oil washing efficiency mainly by emulsification and changing the wettability. The generated oil droplets will play a role in plugging and improving the wave efficiency. However, tight reservoirs have the characteristics of large pores and small throats, and curved and necking throats are developed, greatly reducing permeability. The microbial recovery efficiency was lower under shorter cultivation times. This study provides a practical basis for the application of consortium bacteria in tight oil fields to enhance recovery. [ABSTRACT FROM AUTHOR]

Currently, microbial enhanced oil recovery (MEOR) is of great interest because of its potential high efficiency and low environmental impact. Biosurfactants, in the purified form or contained in the bacterial cultural media, are one of the promising directions in MEOR because they are more stable in response to different environmental factors than life microorganisms are. However, the extraction and purification of biosurfactants, as well as their working concentrations and efficacy in real oilfield conditions remain a challenge. In the present work, cultural media of two novel bacterial isolates (Bacillus pumilus and Peribacillus simplex) were used in a model experiment with sand pack columns to enhance the recovery of heavy oil from Romashkino oilfield (Russia). Using FTIR and TLC methods, it was demonstrated that both cultural media contained lipopeptides. In the genome of both bacterial isolates, genes srfAA, fenD and bamC encoding synthesis of surfactin, fengycin, and bacillomycin, respectively, were revealed. The oil recovery efficacy of cell-free cultural media after 24 h of cultivation was 34% higher and 16% lower as compared with synthetic surfactant for B. pumilus and P. simplex, respectively. It can be concluded that the high-cost step of biosurfactants separation and purification may be excluded, and cell free cultural media of the isolates may be directly used in field conditions to enhance the recovery of heavy oils. [ABSTRACT FROM AUTHOR]

Microbial Enhanced Oil Recovery (MEOR) is an option for recovering oil from depleted reservoirs. Numerous field trials of MEOR have confirmed distinct microbial community structure in diverse production wells within the same block. The variance in the reservoir microbial communities, however, remains ambiguously documented. In this study, an 8 m long core microbial flooding simulation device was built on a laboratory scale to study the dynamic changes of the indigenous microbial community structure in the Qizhong Block, Xinjiang oil field. During the MEOR, there was an approximate 34% upswing in oil extraction. Based on the 16S rRNA gene high-throughput sequencing, our results indicated that nutrition was one of the factors affecting the microbial communities in oil reservoirs. After the introduction of nutrients, hydrocarbon oxidizing bacteria became active, followed by the sequential activation of facultative anaerobes and anaerobic fermenting bacteria. This was consistent with the hypothesized succession of a microbial ecological "food chain" in the reservoir, which preliminarily supported the two-step activation theory for reservoir microbes transitioning from aerobic to anaerobic states. Furthermore, metagenomic results indicated that reservoir microorganisms had potential functions of hydrocarbon degradation, gas production and surfactant production. Understanding reservoir microbial communities and improving oil recovery are both aided by this work. [ABSTRACT FROM AUTHOR]

This comprehensive review examines iturin, a cyclic lipopeptide originating from Bacillus subtilis and related bacteria. These compounds are structurally diverse and possess potent inhibitory effects against plant disease-causing bacteria and fungi. Notably, Iturin A exhibits strong antifungal properties and low toxicity, making it valuable for bio-pesticides and mycosis treatment. Emerging research reveals additional capabilities, including anticancer and hemolytic features. Iturin finds applications across industries. In food, iturin as a biosurfactant serves beyond surface tension reduction, enhancing emulsions and texture. Biosurfactants are significant in soil remediation, agriculture, wound healing, and sustainability. They also show promise in Microbial Enhanced Oil Recovery (MEOR) in the petroleum industry. The pharmaceutical and cosmetic industries recognize iturin's diverse properties, such as antibacterial, antifungal, antiviral, anticancer, and anti-obesity effects. Cosmetic applications span emulsification, anti-wrinkle, and antibacterial use. Understanding iturin's structure, synthesis, and applications gains importance as biosurfactant and lipopeptide research advances. This review focuses on emphasizing iturin's structural characteristics, production methods, biological effects, and applications across industries. It probes iturin's antibacterial, antifungal potential, antiviral efficacy, and cancer treatment capabilities. It explores diverse applications in food, petroleum, pharmaceuticals, and cosmetics, considering recent developments, challenges, and prospects. [ABSTRACT FROM AUTHOR]

During microbial-enhanced oil recovery (MEOR), surfactant-producing microorganisms are reported to improve displacement efficiency. However, the sweep efficiency could be improved by emulsified droplets or be reduced by low-IFT (interfacial tension)-induced fingering flow. Therefore, whether sweep efficiency can be improved by surfactant-producing microorganisms is currently unclear. To reveal the EOR mechanisms by surfactant-producing microorganisms, a 2D micro-model was used to conduct a long-term pore-scale experiment. In the results, 19.4% of the original oil in place (OOIP) was recovered, and surfactant-producing microorganisms can improve not only displacement efficiency (16.9% of the OOIP in the main stream) but also sweep efficiency (27.7% of the OOIP in the margin). Furthermore, the sweep efficiency was improved during flooding and shut-in periods. For instance, 19.5% of the OOIP in margins migrated to the main stream during the 1st shut-in period. Regarding mechanisms of sweep, it was improved by Jamin's effect during the flooding period, while during the shut-in period, the oil migration was attributed to the spontaneously spreading biomass and their wettability altering the biosurfactant. This long-term experiment revealed that the dominant oil recovery mechanisms were altering with declining oil saturation, based on which sweep efficiency contributed to oil recovery only at oil saturation higher than 40.5%. While at lower oil saturation, only displacement efficiency could be improved. [ABSTRACT FROM AUTHOR]

After polymer flooding, substantial oil and residual polymers remain in reservoirs, leading to plugging and reduced recovery. MEOR (Microbial Enhanced Oil Recovery) aims to release trapped oil by utilizing microorganisms and their byproducts. The microorganisms can use residual HPAM (hydrolyzed polyacrylamide) as an energy source for polymer degradation, addressing reservoir plugging issues and improving oil recovery. However, microorganisms are sensitive to environmental conditions. This paper presents a detailed update of MEOR, including microbial products, mechanisms, and merits and demerits. The effect of the displacement fluid and conditions on microorganisms is thoroughly demonstrated to elucidate their influencing mechanism. Among these factors, HPAM and crosslinkers, which have significant biological toxicity, affect microorganisms and the efficiency of MEOR. Limited research exists on the effect of chemicals on microorganisms' properties, metabolism, and oil displacement mechanisms. The development of microbial consortium, their metabolic interaction, and oil displacement microprocesses are also discussed. In addition, prior studies lack insights into microorganisms' interaction and mechanisms using chemicals. Finally, field trials exist to examine the microbial consortium's efficiency and introduce new technologies. This review mainly explores the influencing factors on microorganisms, and confirms the credibility of MEOR after polymer flooding, providing a scientific basis for improving the theory of MEOR. [ABSTRACT FROM AUTHOR]

The combination of strains of different species and genera may enhance the effects of single bacteria, surpass the tolerance upper limit, and optimize the viscosity reduction and degradation. In this study, six strains were isolated in low permeability layers of the Ordos Basin and were combined to verify the effect of the consortium strains. The selected single strains have good emulsifying and viscosity-reducing effects, but their degradation components are different. SC4561 (Bacillus cereus), SC4551 (Bacillus sp.), and H-1 (Brevibacillus sp.) form consortium A, and SC4534 (2) (Bacillus sp.), SC4542 (Bacillus licheniformis), and A-3 (Bacillus licheniformis) form consortium B. The performance of the mixed strains was evaluated by the analysis of change in emulsification rate, crude oil composition, viscosity, and the tolerance (temperature, salinity, and pH) through GC-MS, rotational rheometer, and other methods. The results showed that the temperature tolerance of the consortium strains was improved by 5-7°C. Consortium B had higher emulsibility ( E 24 was higher than 40% in average) and viscosity degradation (above 35%), and the crude oil in consortium B has almost no wall adhesion. The components of crude oil that consortia use were still diverse, including both long- and short-chain hydrocarbons. However, the proportion of long-chain n-alkanes is further reduced compared with that of single bacteria, and the highest ratio was reduced by 23.81% (B-ALL). At the same time, they also had effects on aromatic hydrocarbons with complex structures (phenanthrene and phenanthrene). This research confirms the enhanced effect of consortium bacteria on single bacteria, facilitating the implementation of microbial enhanced oil recovery technology in the future. [ABSTRACT FROM AUTHOR]

A complex microbial community exists in oil reservoirs after the application of chemical enhanced oil recovery (EOR) technologies, where the dynamic interactions of microorganisms are thought to be critical to petroleum composition, recovery, and production technologies but are poorly understood. Here, we used the 16S rRNA gene to construct co-occurrence networks for bacterial and archaeal communities associated with water-, polymer-, and alkaline surfactant polymer (ASP)-flooded oil reservoirs. Nonmetric multidimensional scaling analysis showed that bacterial and archaeal community structures differed significantly (p < 0.01) among the oil reservoirs with different EOR compositions. The microbial co-occurrence pattern in water-flooded reservoirs was more complex, with more nodes, edges, and average degrees (i.e., average links per node in the network) than in the polymer- and ASP-flooded reservoirs. However, the archaeal co-occurrence pattern maintained a more robust structure than that of bacteria under the application of polymer and ASP flooding technologies, suggesting that the application of different enhanced oil recovery techniques has diverse effects on the bacterial and archaeal co-occurrence patterns in reservoirs. The pH and [HCO 3 −] were significantly correlated with the variations in bacterial and archaeal network structures. Our findings provide new insights into the response of microbes to diverse EOR processes by regulating their interactions in deep oil reservoirs. Revealing the effects of water, polymer, and ASP flooding on the co-occurrence patterns of bacteria and archaea in oil reservoirs, which may facilitate the implementation of microbial enhanced oil recovery technology in the future. [Display omitted] • Microbial co-occurrence pattern in water flooded were more complex than in EOR flooded oil reservoirs. • Archaeal maintained more robust structure compared with bacteria under the application of polymer and ASP flooding technologies • pH and HCO 3 - explained major variations in bacterial and archaeal network structure in oil reservoirs. [ABSTRACT FROM AUTHOR]

This paper investigates the relevant mechanisms of microbial propagation and oil displacement, summarizes the characteristics of different microbial enhanced oil recovery technologies, and on this basis, introduces the research progress of microbial enhanced oil recovery in complex oil and gas reservoir environments such as low permeability, high viscous oil, high temperature and pressure, high water content, and high salinity, and looks forward to the future development direction of microbial oil displacement in different oil and gas reservoirs. It provides the corresponding theoretical basis and research reference for the relevant researchers. [ABSTRACT FROM AUTHOR]

The biosphere is subjected to low temperatures in both aquatic and terrestrial environments. Psychrophilic and psychrotolerant bacteria that colonize cold environments, such as Antarctica and Arctic continents, are able to survive in inhospitable conditions. This is attributed to some cold adaptations developed by these microorganisms over the years, such as the synthesis of carotenoid pigments, modification of membrane structure and production of biosurfactants (BS) and/or bioemulsifiers (BE). BS and BE are bioproducts produced by microorganisms that are less toxic than chemically synthesized surfactants. The physical and chemical properties of these substances make them applicable in different areas, such as bioremediation of contaminated areas, microbial enhanced oil recovery, pharmaceutical, cosmetics and food industries. Additionally, studies about BS and BE produced by psychrophiles and psychrotolerants are still very recent in relation to the studies carried out with mesophilic microorganisms and their products. This review aims to compile information on the mechanisms of adaptation of microorganisms in cold environments with a focus on the production of BS and BE and their potential biotechnological applications. [ABSTRACT FROM AUTHOR]

Microbial enhanced oil recovery (MEOR) is a tertiary oil recovery process that manipulates the microbial environment inside oil reservoirs to modify the physical/chemical properties of the reservoirs to enhance the oil recovery. Up to now, the detailed MEOR mechanism is still not entirely clear due to the multiple influence factors (e.g., pH, nutrients, temperature, porosity, and permeability) on microbial growth and reproduction, as well as the lack of understanding of microbial's influencing mechanism on the oil recovery process. In this study, a Bacillus subtilis‐based MEOR process was conducted in a polymethyl methacrylate (PMMA)‐based microfluidic device to mimic the MEOR process in the reservoir. The porous microstructure based on real sandstone slice images was fabricated with laser ablation on a PMMA substrate. Two different MEOR approaches were conducted in the PMMA‐based microfluidics devices: the direct injection of displacing reagent (biosurfactant produced by bacteria) into the microfluidic chip for the oil recovery (ex‐situ), and the incubation of bacteria solution inside the chip followed with brine flooding (in‐situ). The result indicates the ex‐situ MEOR process with B. subtilis can reach a recovery rate of 38.56%, while the in‐situ MEOR process with B. subtilis reached a recovery rate of 40.27%. The proposed study provides a new tool for understanding the MEOR process, with advantages in visibility and accurate fluid control during the MEOR process. [ABSTRACT FROM AUTHOR]

Microbial enhanced oil recovery (MEOR) is an important tertiary recovery technology to recover oil, especially heavy oil, from reservoirs. However, MEOR often fails to achieve satisfactory oil recovery in the field applications because of utilization of unsuitable microorganisms and nutrients. Recent studies proved the existence of microbes inside oil ("oil-phase" microbes) and their potential for application in MEOR. To validate this concept, we isolated microbes from the "oil-phase" of crude oil samples. With them, a synthetic four-member microbial consortium K, was selected to use in an experiment of core flooding, which showed a beneficial capacity for improving oil recovery. Furthermore, the consortium K and nutrients were applied in a field trial of microbial huff and puff in an extra heavy oil recovery. Results demonstrated the incremental cumulative oil production of two high water-cut (99%) shut-in wells reached 1078.8 t and 791.6 t, respectively, with the effective period of 14 months, while the viscosity of heavy oil had significantly declined decreased by 50%. In conclusion, our findings clearly demonstrate that the great potential of a novel methodology to use indigenous "oil-phase" microbes as seedbanks for improving oil recovery in extremely viscous oil reservoirs with high water-cut. [ABSTRACT FROM AUTHOR]

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. This study is one of a kind that showed successful tertiary recovery of crude oil through indigenous microbial consortia. In this study, a medium was optimized to allow ideal microbial growth under reservoir conditions through RSM. Once the nutrient recipe was optimized, the microbial metabolites were estimated through gas chromatography. The maximum amount of methane gas (0.468 mM) was produced in the TERIW174 sample. The sequencing data set showed the presence of Methanothermobacter sp. and Petrotoga sp. In addition, these established consortia were analyzed for their toxicity, and they appeared to be safe for the environment. Furthermore, a core flood study showed efficient recovery that was ~25 and 34% in TERIW70 and TERIW174 samples, respectively. Thus, both the isolated consortia appeared to be suitable for the field trials. [ABSTRACT FROM AUTHOR]

The crude oil reserves in Oman mainly consist of heavy oil. Microbial enhanced heavy oil recovery (MEOR) has been proved to be an efficient technique in the tertiary heavy oil recovery. Five Bacillus species potential for enhanced heavy oil recovery (EHOR) were isolated and the biodegradation ability of these isolates was studied. As heavy crude oil comprises of aromatic hydrocarbons rather than aliphatic ones, the aromatic catabolism gene, catechol 2,3-dioxygenase (C23O) and catechol 1,2-dioxygenase (C12O) were the genes of interest in this study along with the reference gene, 16S rDNA. The copy number variation of these genes was determined using droplet digital PCR (ddPCR). The primers and probes for ddPCR assay were designed targeting these genes. It was observed that the heavy crude oil biodegradation potential of the isolates correlated with the copy number of C23O gene in the microbial genomes. The isolate, Paenibacillus ehimensis BS1 had the highest C23O gene copy number (1.057) followed by Bacillus firmus BG4 (0.895) and Bacillus halodurans BG5 (0.031) as demonstrated by their biodegradation potential. This is one of the few studies deploying ddPCR in the field of heavy crude oil biodegradation by spore forming bacteria. [ABSTRACT FROM AUTHOR]

The fermentation conditions of Pseudomonas aeruginosa strain were optimized, the optimal culture medium is obtained as follows: Canola oil 80 g/L,NaNO3 6 g/L,Na2HPO4·12H2O 3 g/L,KH2PO4 1.5 g/L,MgSO4 0.36 g/L,FeSO4·7H2O 0.2 g/L,CaCl2 0.12 g/L.The optimum culture conditions are as follows: temperature 37 ℃,liquid volume 40 mL/250 mL,fermentation time 168 h.The average rhamnolipid yield is 57.83 g/L and the surface tension is 27.89 mN/m.At the same time, the physicochemical properties of rhamnoid are found to be stable in the environment of relatively harsh temperature, salinity and pH.In the physical simulation experiment, a new bio-oil displacement system is established by using fermentation broth and adding xanthan gum, a bio-polymer with viscous properties.Compared with water flooding, the recovery rate of 5% rhamnoid fermentation broth biocomposite system can be increased by 17.4%,indicating that it has a great application prospect in microbial oil recovery field [ABSTRACT FROM AUTHOR]

• The wettability alteration by using microbial and low-salinity solutions was investigated. • Different concentrations of MgCl 2 , CaCl 2 , KCl, and NaCl solutions were used and Acinetobacter lactucae strain was used. • Theoretical mechanistic method was used to calculate disjoining pressure and confirm contact angle measurements. Microbial enhanced oil recovery (MEOR) and low salinity water flooding have been identified as effective environmentally friendly approaches to enhance oil recovery in different reservoirs. Due to the complexities of behaviors of microorganisms and ions, the impact of low salinity water and MEOR on oil recovery mechanisms is not yet well understood. The present work attempts to study the impact of these approaches on wettability alteration through the measurement of contact angle and zeta potential, as well as theoretical analysis of surface forces. In addition, several lab core flooding scenarios are defined to evaluate the oil recovery and the combination of low salinity water flooding and MEOR increased oil recovery to more than 44 %. In this study, disjoining pressure, which is known as summation of structural forces, electrostatic double layer repulsive forces, and van der Waals attractive forces, is employed to determine the impact of ion types (MgCl 2 , CaCl 2 , NaCl, and KCl), concentration (500, 2000, and 4000 ppm) and presence of Acinetobacter lactucae (Ib-30) microorganism on oil recovery mechanisms. The results implied that the disjoining pressure profile is more sensitive to ion types rather than their concentrations. Moreover, removing divalent ions would have a positive effect on the wettability alteration, and there was an interesting consistency between contact angle measurements and disjoining pressure isotherms. [ABSTRACT FROM AUTHOR]