Microbial Enhanced Oil Recovery Process Research Articles

Production, characterization, and application of Pseudoxanthomonas taiwanensis biosurfactant: a green chemical for microbial enhanced oil recovery (MEOR)

Biosurfactants, as microbial bioproducts, have significant potential in the field of microbial enhanced oil recovery (MEOR). Biosurfactants are microbial bioproducts with the potential to reduce the interfacial tension (IFT) between crude oil and water, thus enhancing oil recovery. This study aims to investigate the production and characterization of biosurfactants and evaluate their effectiveness in increasing oil recovery. Pseudoxanthomonas taiwanensis was cultured on SMSS medium to produce biosurfactants. Crude oil was found to be the most effective carbon source for biosurfactant production. The biosurfactants exhibited comparable activity to sodium dodecyl sulfate (SDS) at a concentration of 400 ppm in reducing IFT. It was characterized as glycolipids, showing stability in emulsions at high temperatures (up to 120 °C), pH levels ranging from 3 to 9, and NaCl concentrations up to 10% (w/v). Response surface methodology revealed the optimized conditions for the most stable biosurfactants (pH 7, temperature of 40 °C, and salinity of 2%), resulting in an EI24 value of 64.45%. Experimental evaluations included sand pack column and core flooding studies, which demonstrated additional oil recovery of 36.04% and 12.92%, respectively. These results indicate the potential application of P. taiwanensis biosurfactants as sustainable and environmentally friendly approaches to enhance oil recovery in MEOR processes.

Uses of Microorganisms in The Recovery of Oil and Gas

Microscopic organisms are the only single-celled organisms proposed for the advancement of techniques for Estimation of Oil Recovery (EOR) because they have numerous desirable properties, including a simple structure and an unsustainable growth rate when supplied with vital nutrients, resulting in the release of metabolic chemicals like Aerosols, acids, minimum lubricants, surfactants, and polymers. Clostridium acetobutylicum was isolated from intensive rice cultivation soil and has the ability to use polysaccharides such as starch and carboxylmethyl cellulose to produce biobutanol, while Desulfovibrio hydrocarbonoclasticus was isolated from marine sediment in Iraq and grows in anaerobic synthetic seawater medium with the addition of a trace element solution. These bacteria can also withstand difficult conditions High salinity, high pressure, and high temperature play roles and contribute to underground geological formations. An aqueous mixture of nutrients, Clostridium acetobutylicum, Desulfovibrio hydrocarbonoclasticus, and molasses with nutrient and bacterial spore injection into a reservoir. As a result, these microorganisms are capable of considerable catalytic reactions. production of a diverse spectrum of products (biosolvents, bioacids, biogases, and biosurfactants) from relatively simple nutritional compounds, multiply vigorously under favourable conditions, and have resulted in increased oil release from reservoir rock. The well began producing 70 days after the medication was started. 80 to 90 days after the injection began, relatively brief polyunsaturated fats, Carbon dioxide, and residues of ethanol, 1-butanol, and acetone were detected. Because of their highly resistant endospores, Clostridium are the most ideal of the several microbes used in MEOR (Microbial enhanced oil recovery). Desulfovibrio strains capable of producing biosurfactants in situ, which are beneficial to the MEOR process, are also valuable. Nutrients are often supplied as fermentable carbs to promote microbial metabolism.

Metagenomic analysis of the microbial community at the Riutort oil shale mine (NE Spain): Potential applications in bioremediation and enhanced oil recovery

Preservation of the environment of the Riutort oil shale mine for more than a century has favored the presence of a paradigmatic ecosystem of oil-degrading microorganisms. After extensive sampling and analysis by 16S rRNA sequencing, a marked prokaryotic community comprising diverse groups of bacteria (genus such as Methylobacter, Thiothrix, and Desulfobacca) and archaea (e.g., Methanobrevibacter genus) with hydrocarbon-degrading activity was found. Aerobic microorganisms were predominant in several samples but facultative microorganisms were also present, and there was an interesting transition to strict anaerobic conditions in some areas. One of the samples contained oil degrading aerobic bacteria such as Pseudomonas spp. and Brevundimonas spp. Of the microbes studied, we conducted a laboratory assessment of the capacity of this specific consortium for bioremediation of petroleum-polluted soil and microbial enhanced oil recovery processes. To this end, we used oily sludge-contaminated soil from La Libertad Refinery and cores from the Ancón Field, respectively, both sites in southwestern Ecuador. The Riutort consortium degraded 50.8% of total petroleum hydrocarbons, 64.2% of saturates, 41.3% of aromatics, and 37.4% of polar compounds after a 60-day incubation using oily sludge as the sole source of carbon. The performance of this consortium reflects its notable potential for bioremediation purposes. In turn, flooding with the natural Riutort consortium and its metabolites achieved a 7.2% (v/v) incremental recovery of crude oil through a sand-pack assay. These results are comparable to those reported using synthetic bacterial consortia, and thus reveal the great interest of the study seepages, not only for understanding microbial activities in oil degradation but also their use in biotechnological applications.

Enhanced Oil Recovery Using Indigenous Microbiome of High Temperature Oil Reservoirs.

Crude oil is a primary energy source used for economic expansion across the world. Secondary recovery processes employed by industries to recover oil from oil wells leave behind 70% of the oil trapped in marginal and deleted zones of reservoirs. To recover the oil from depleted zones, microbial enhanced oil recovery (MEOR) tertiary processes were introduced, which involve the production of metabolites from the indigenous microbiome. In this study, the indigenous microbiota was identified as Marinobacterium sp., Silvanigrella sp., Petrothermobacter sp., Pseudomonas sp., Bacillus sp., Nitrincola sp., Halomonas sp., Uncultured Roseovarius sp., and Phaeobacter. Further, the secondary metabolites such as volatile fatty acids (ethanol, acetone, and acetate), biomass, gases (CO2, CH4), and biosurfactants were estimated through gas chromatography and FTIR spectroscopy. Once stable microbial growth was attained in the baltch media, it was optimized through response surface methodology (RSM) to minimize the process cost. The optimized media with 9g/L of molasses, 1.75g/L of sodium bicarbonate, and 1.25g/L of ammonium chloride showed a significant impact on metabolite production. Additionally, core flood studies to simulate field studies were performed that represented that TeriK-1 brought a significant increment of 18.9%, which makes it suitable for MEOR field implementation. This study is one of its kind where the indigenous thermophilic sp. was successfully established and is capable of producing the secondary metabolites that aid in the MEOR process.

Examining the effect of reservoir conditions on efficiency of microbial enhanced oil recovery processes using Rhodococcus erythropolis strain; experimental approach

Examining the effect of reservoir conditions on efficiency of microbial enhanced oil recovery processes using Rhodococcus erythropolis strain; experimental approach

Analyzing the microbial factors affecting microbial enhanced oil recovery through numerical simulation study

ABSTRACT Primary and secondary recovery methods are usually not sufficient to maximize the oil recovery. In many cases, more than 40% of the Oil Initially in Place is left in the reservoir after implementing these recovery methods. To resolve the issue at hand, petroleum engineers have at their disposition a plethora of tertiary recovery methods such as chemical flooding, thermal recovery, and microbial enhanced oil recovery (MEOR). In this study, we propose the use of MEOR: a technique that uses naturally occurring microbes in the reservoir or injected microbes to enhance the oil recovery. The MEOR process is governed by several mechanisms such as viscosity reduction, relative permeability alteration, capillary pressure alteration, and other reaction-induced system changes such as pressurization. This study investigates the impact of these mechanisms on the hydrocarbon production by conducting a numerical simulation using our in-house MEOR numerical simulator. In the base case study, the case with MEOR shows the 20% of oil production improvement than the case without MEOR. We conduct a sensitivity analysis to evaluate the impact of microbial factors affecting MEOR to the system responses and production behavior, where the maximum growth rate of microbes is found to be the most influential factor with the scaled sensitivity coefficient of 1.384 × 105. The findings provide the relative impacts of factors affecting the performance of MEOR, which subsequently suggest the factors to be investigated with emphasis for oil production improvement in the MEOR applications.

SELECTED INDONESIAN MICROBES POTENTIALS FOR MEOR

Oil recovery can be increased through the activities of microbes in a process known as Microbial Enhanced Oil Recovery (MEOR). MEOR technology has been implemented in a number of oil producing companies and has proven to have a good prospect, environmentally friendly and low cost. The microbes which proliferate in Indonesian oil fields should be subjected to laboratory identification. Samples of formation water, oil, and soil were taken from various oil fields. These oil fields were selected on account of their reservoir temperatures which promise optimum growth of microbes. In order that MEOR can be applied in these oil fields, the existing microbes in their oil wells were isolated and identified. Based on the results of isolation and identification activities several indigenous bacteria species were obtained from the oil well environment. The potential of each bacteria species for use in MEOR process depends on their ability to live and grow in the reservoir environment as well as the bioproducts produced, such as biosurfactant, bioacid, and biosolvent. The bioproducts produced depend on the inherent capability of the isolate as well as the support of the medium and environmental condition. From the tests of their capability to grow in hydrocarbons, and live in semianaerobic condition, 12 isolates, were selected and some isolates were found to produce such bioproducts. The selected microbes and nutrient have been experimented by using microbial core flooding apparatus. The result has a good prospect for implementation in the oil field.

Predicting performance of in-situ microbial enhanced oil recovery process and screening of suitable microbe-nutrient combination from limited experimental data using physics informed machine learning approach

Screening of suitable microbe-nutrient combination and prediction of oil recovery at the initial stage is essential for the success of Microbial Enhanced Oil Recovery (MEOR) technique. However, experimental and physics-based modelling approaches are expensive and time-consuming. In this study, Physics Informed Machine Learning (PIML) framework was developed to screen and predict oil recovery at a relatively lesser time and cost with limited experimental data. The screening was done by quantifying the influence of parameters on oil recovery from correlation and feature importance studies. Results revealed that microbial kinetic, operational and reservoir parameters influenced the oil recovery by 50%, 32.6% and 17.4%, respectively. Higher oil recovery is attained by selecting a microbe-nutrient combination having a higher ratio of value between biosurfactant yield and microbial yield parameters, as they combinedly influence the oil recovery by 27%. Neural Network is the best ML model for MEOR application to predict oil recovery (R2≈0.99).

Biosurfactant production using Egyptian oil fields indigenous bacteria for microbial enhanced oil recovery

Biosurfactant production is one of the most efficient mechanisms in microbial enhanced oil recovery (MEOR) processes. This work investigates the production of biosurfactants by indigenous bacteria isolated from Egyptian oil fields, and how to optimize these produced biosurfactants for MEOR. 59 Egyptian oil reservoirs were screened to evaluate the potential applicability of MEOR processes, based on their rock and fluid properties. Results showed that 8 reservoirs from the Gulf of Suez and 3 reservoirs from the Western Desert had the potential to MEOR. Combined analysis of morphological, and biochemical characterization was performed on the 11 bacterial strains isolated from different crude oil samples collected from the reservoirs that have the potential to MEOR process to identify their types. Bacillus spp, a bacilli species that can produce biosurfactants, was selected for further studies. To optimize the surface activity of the produced biosurfactant, ten different reported nutrient media, and a new proposed nutrient media were examined. Bacillus spp has shown the ability to produce a very active biosurfactant that reduced the surface tension of water from 71.8 ± 1.9 mN/m to 25.7 ± 1.2 mN/m, and the interfacial tension of water against kerosene from 48.4 ± 2.1 mN/m to 0.38 ± 0.07 mN/m at Critical Micelle Concentration (CMC) of 0.04 ± 0.01 g/l, in a medium supplemented by the new proposed nutrient medium H. The growth rate of Bacillus spp was studied, and it was found it reached its maximum (OD600nm 2.59 ± 0.16) after 24 h of incubation. Biosurfactant production has no significant change in its surface activity over a wide range of temperature range up to 120 °C, which means the studied species Bacillus spp is a thermophilic bacterium. Bacillus spp grew well in the presence of high salt concentration up to 20% (w/v) NaCl, the optimal surface activity was obtained in the range of 0–2% (w/v) NaCl, and at pH 7. The emulsification activity of the produced biosurfactant was examined, and it reached the maximum (69.6 ± 1.5%) against kerosene at temperature 25 °C, Salinity 0% (w/v) NaCl (distilled water), and pH 7. The produced biosurfactant was purified and extracted by acid precipitation method, and the biosurfactant yield of the purified compound was found to be 2.8 ± 0.3 g/l. Finally, the core-flooding experiments were conducted to investigate the effect of produced biosurfactants by Bacillus subtilis in oil recovery. The obtained results reveal the potential of Bacillus spp to grow in the new proposed medium H and produce effective and efficient biosurfactants that enhanced oil recovery by 25.19–39.35% of additional oil over the water flooding residual oil saturation in the studied cores and retain more than 60% of its surface activity under harsh conditions and that are relevant to Microbial Enhanced Oil Recovery, MEOR.

Risk Mitigation and Mapping on Tubular System During Microbial Huff and Puff Injection Coupled with Lean Six Sigma Approach at Field X

Increasing demand of oil in Indonesia is in contrast with the decreasing oil production every year. Enhanced oil recovery (EOR) has become one of the most favorable method in maximizing the production of mature fields with various applications and research has been done on each type, especially microbial EOR (MEOR). “X” field is a mature oil field located in South Sumatra that has been actively producing for more than 80 years and currently implementing MEOR using huff and puff injection. However, there are some potential risks regarding MEOR processes that may inhibit the production by damaging the well’s tubular system, particularly microbially induced corrosion (MIC). This study reviews the risk mitigation and mapping to prevent corrosion on tubular system during MEOR huff and puff processes, equipped with the approach of Lean Six Sigma.The mitigation and mapping process follow the framework of define, measure, analyze, improve, and control (DMAIC). It starts with defining the problem using supplier-input-process-output-customer (SIPOC) diagram after all the field data necessary has already been collected, then measuring the corrosion rate model using ECE™ software as well as conducting sensitivity analysis of the fluid rates. The analyze phase involves constructing fishbone diagram to identify the root causes, comparison with industry’s specification and standard, and analysis of chromium effect on corrosion rates. Further simulation is conducted to support the analysis and to ensure the improvements and sustainability of the design selection.Based on the simulation results, the normal corrosion rate ranging from 0.0348 – 0.039 mm/year and the pH is around 4.03 – 5.25, while the ±30% fluid rate sensitivity results shown that the change of water flowrate is more sensitive than oil flowrate with the corrosion rate approximately 0.0275 – 0.048 mm/year. The fishbone diagram identifies that material selection and environmental condition as the main root causes, then corrosion resistant alloy (CRA) is used in the tubing string to prevent corrosion in the future by using super 13Cr martensitic steel (modified 2Ni-5Mo-13Cr) as the most suitable material. Further simulation on chromium content supports the selection that corrosion rate can be reduced by adding the chromium content in the steel. The completion design is then capped with choosing the Aflas® 100S/100H fluoro-elastomer as the optimum material for packer and sealing. Overall, the Lean Six Sigma approach has been successfully applied to help the analysis in this study.

Systematic modelling incorporating temperature, pressure, and salinity effects on in-situ microbial selective plugging for enhanced oil recovery in a multi-layered system

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.

Stochastic assembly process dominates bacterial succession during a long-term microbial enhanced oil recovery

Microbial enhanced oil recovery (MEOR) has been successfully used in oil exploitation to increase oil production. However, the mechanisms of microbial interactions and community assembly related to oil production performance along MEOR process are poorly understood. Here, we investigated the microbiome of an oil reservoir for a period of 5 years under three phases of different treatments with the injection of a mixture of microbes, nutrients, and air at different intensity. During the MEOR process, amplification of functional genes revealed an increase of genes related to hydrocarbon degradation linked to methanogenesis, supported by stable isotope analysis for confirmation of the methanogenesis activity. Meanwhile, a lower contribution of the ubiquitous/common taxa, closer and more positive associations, and lower modularity were observed in bacterial co-occurrence networks, with the rare taxa being the keystone taxa. The null model analysis and structural equation modeling revealed that the contribution of stochastic processes affected by functional groups and co-occurrence patterns to bacterial community increased significantly with the increase of oil production. This provides new insight that stochastic assembly in bacterial community increased along with MEOR process, and it is worthwhile paying attention to the uncertain consequences caused by random evolution since the treatment effect of MEOR is closely related to the in-situ community in oil reservoir.

Production, characterization and application of biosurfactant produced by Bacillus licheniformis L20 for microbial enhanced oil recovery

Microbial enhanced oil recovery (MEOR) is one of significant EOR methods which applies microbes and their products to recover crude oil from reservoirs. Biosurfactant is an amphiphilic microbial product, which plays a key role in the MEOR process thanks to its optimal interfacial properties. Besides, biosurfactant has advantages of environmentally friendly compared to petroleum-based surfactants due to its higher biodegradability and lower toxicity. In this study, biosurfactant produced by Bacillus licheniformis L20 was optimized by using various carbon sources. The highest emulsification index was obtained by using lactose based mineral salt solution. The biosurfactant obtained was characterized by the FTIR and UPLC-Q-TOF/MS, the characterization results indicated that this biosurfactant was a series of lipopeptides containing C13-, C14-, C15-, C16-surfactin and other types of lipopeptides. Furthermore, the ability of this biosurfactant for EOR was evaluated through wettability alteration measurement, emulsion stability determination and the core flooding experiments. Those results showed that the biosurfactant altered the wettability of the hydrophobic surface of core slices with different permeability to more water-wet. This biosurfactant can maintain emulsification activity in pH 4–11, 85°C, 25 wt% NaCl or 17.5 wt% CaCl2 solution. Moreover, the core flooding experiments with this biosurfactant resulted in a 19.58% increase of oil recovery rate. Therefore, the results obtained from this study demonstrated that this biosurfactant developed had a promising potential for ex-situ MEOR, especially in harsh reservoirs conditions.

Parameters govern microbial enhanced oil recovery (MEOR) performance in real-structure micromodels

Several parameters govern the oil displacement efficiency during microbial enhanced oil recovery (MEOR) processes. These parameters can be classified into four main parameters including (1) microbial growth, which is controlled by nutrient concentration and incubation conditions as well as the flooding sequence management, (2) bacteria community, (3) properties of porous media such as pore size and wettability and (4) other parameters. This paper presents the effects of these parameters on MEOR performance during two-phase flooding experiments in micromodels using reservoir fluid from a German high-salinity oil field. New micromodels generated based on μCT images of a Bentheimer core plug were used to investigate the MEOR displacement process under elevated pressure, temperature, and anaerobic and sterile conditions. As a result, it was found that microbial growth and its end-products have a significant role in the oil displacement efficiency during the MEOR process. Based on flooding experiments, a significant effect of bioplugging that improved the macroscopic conformance was observed during the MEOR process. This work gives new insights into the pore-scale mechanisms and factors affecting MEOR performance in porous media. The results presented in this paper could be used to support MEOR studies on a larger scale, such as those in the core plug or sandpack before field implementation.

Isolating, identifying and evaluating of oil degradation strains for the air-assisted microbial enhanced oil recovery process.

Due to the inefficient reproduction of microorganisms in oxygen-deprived environments of the reservoir, the applications of microbial enhanced oil recovery (MEOR) are restricted. To overcome this problem, a new type of air-assisted MEOR process was investigated. Three compounding oil degradation strains were screened using biochemical experiments. Their performances in bacterial suspensions with different amounts of dissolved oxygen were evaluated. Water flooding, microbial flooding and air-assisted microbial flooding core flow experiments were carried out. Carbon distribution curve of biodegraded oil with different oxygen concentration was determined by chromatographic analysis. The long-chain alkanes are degraded by microorganisms. A simulation model was established to take into account the change in oxygen concentration in the reservoir. The results showed that the optimal dissolved oxygen concentration for microbial growth was 4.5~5.5mg/L. The main oxygen consumption in the reservoir happened in the stationary and declining phases of the microbial growth systems. In order to reduce the oxygen concentration to a safe level, the minimum radius of oxygen consumption was found to be about 145m. These results demonstrate that the air-assisted MEOR process can overcome the shortcomings of traditional microbial flooding techniques. The findings of this study can help for better understanding of microbial enhanced oil recovery and improving the efficiency of microbial oil displacement.

Modification Wettability and Interfacial Tension of Heavy Crude Oil by Green Bio-surfactant Based on Bacillus licheniformis and Rhodococcus erythropolis Strains under Reservoir Conditions: Microbial Enhanced Oil Recovery

Oil spill contamination in soil is still problematic. At the same time, petroleum-contaminated soil in oil reservoirs contain various microbes, which have the ability for biosurfactant production. Extracting these biosurfactants is a very promising and cost-effective strategy for the microbial enhanced oil recovery process. Biosurfactants production using Bacillus licheniformis AnBa7 and Rhodococcus erythropolis sp., isolated from Egyptian crude oils, was enhanced using various carbon sources. The best biosurfactant characteristics were observed when 1% of crude oil was used as a carbon source. The production was further improved by using a developed fed-batch cultivation strategy depends on using 1% Glucose as a single addition at the beginning of the culture. Then 1% of crude oil was added three times during the production process. This strategy enhanced surfactin and trehalose productivity by 1.8 and 4.7 fold higher than the normal conditions, respectively. The surface-active and thermodynamic properties were studied. The results indicated that the calculated values of ΔGmic for surfactin complex, and trehalose complex were −18.47 and −18.28 kJ/mol at 60 °C, respectively while ΔGads values were −30.42 and −29.46 kJ/mol at 60 °C. The interfacial tension (IFT) values of surfactin complex and trehalose complex systems were ranging from 0.75 to 0.19 mN m–1 and from 0.93 to 0.26 mN m–1 at 60 °C, respectively. However, the (IFT) for the blank solution was ∼11.57 mN m–1, and the wettability was changed to an excellent water-wet state (θ = ∼ 17.42–24.0°). The core-flooding studies showed that the enhanced oil recovery for surfactin complex and trehalos complex, at maximum concentration 6 g/L, were 59.21% and 51.83%, respectively. A predicted mechanism was illustrating through the text.

Oil washing proficiency of biosurfactant produced by a novel Bacillus tequilensis MK 729017 isolated from Assam reservoir soil

The present study describes elaborately the isolation of a potential biosurfactant producing and crude oil degrading (1-5%) strains isolated from the Assam oil reservoir field. The produced biosurfactant was chemically characterized for its applicability for the enhanced oil recovery applications in terms of wetting, interfacial tension (IFT) and oil washing. From the seven isolated strains, Bacillus tequilensis MK 729017 was chosen based on the better surface active properties as it reduced the surface tension to 30 ± 2 mN/m along with a moderate emulsification index of 66 ± 2 %. The produced biosurfactant was chemically identified to be lipopeptide, surfactin with a lower critical micelle concentration value of 90 mg/L. The carbon source and environmental parameters were optimized for the maximum concentration of the biosurfactant using RSM-CCD. The maximum biosurfactant concentration was measured to be 7.46 ± 0.39 g/L and Y_PS was determined as 0.45. The specific growth rate of the isolate was 0.15 ± 0.01 h-1 and Y_XS was estimated as 0.1. The produced biosurfactant was also found to be thermal and colloidal stable. The biosurfactant solutions altered wettability of hydrophobic rock surface from 90 ± 1o to 26 ± 1o indicating a better interfacial interaction. The IFT of the produced biosurfactant was found to be 0.32 ± 0.02 mN/m. The oil washing efficiency (80 ± 2 %) of the produced surfactin was comparable with chemical surfactants and the process involved two-steps: initial a faster (surface) washing followed by a slower (internal) washing. The first process was dependent on micelle sizes, while the later was dependent on water-oil emulsion size. The lower emulsion size of surfactin contributed to a greater internal washing as compared to chemical surfactants. These observations endorse the potential of the isolated strain towards biosurfactant production and its application in microbial enhanced oil recovery process.

Influence of crucial reservoir properties and microbial kinetic parameters on enhanced oil recovery by microbial flooding under nonisothermal conditions: Mathematical modelling and numerical simulation

In the present study, improved mathematical and numerical models are developed in order to simulate the influence of important reservoir (effective porosity and longitudinal dispersivity), fluid and microbial kinetic (Monod half-saturation constant, substrate to biomass yield coefficient and substrate inhibition) parameters on dynamics of in-Situ microbial enhanced oil recovery (MEOR) processes using Bacillus sp. in a typical sandstone reservoir. This numerical model is a novel attempt to consider the coupled effects of heat transport and substrate-inhibition kinetics on reactive-transport of microbes, substrates and biosurfactants as against the conventional models, thus making the prediction of MEOR processes more realistic and may assist in developing suitable strategies to enhance oil recovery at field scale. In addition, the present model also investigates the changes in relative permeabilities of reservoir fluids (oil and water) and fractional flow of water under the influence of nonisothermal condition, substrate inhibition, along with variations in pore-size distribution index, oil to water viscosity ratio and crude oil API gravity within reservoir during microbial flooding for estimating residual oil recovery. The present model results match significantly well, when verified, with the existing analytical and experimental results, thus proving the model's reliability. The results suggest that under nonisothermal conditions, biosurfactant production is maximum (77.8 mg ml−1) at effective reservoir porosity 23.4%, with low substrate half-saturation constant and high substrate-to-biomass yield coefficient values of 0.018 mg ml−1 and 0.8, respectively. Though biosurfactant production is reduced by more than 80% due to substrate inhibition, which is maximum at inhibition constant value 0.1 mg ml−1, residual oil-saturation is decreased by more than 90% at the end of MEOR process, thus enhancing oil displacement, mobility and hence, improved crude oil recovery. The reactive-transport of substrates, microbes and biosurfactants at injection mean fluid velocity of 1.68 m day−1, are also found to be highly sensitive to reservoir longitudinal dispersivity (αL) and maximum biosurfactants are produced (9.74 mg ml−1) at threshold αL value, 0.37 m, which corresponds to reservoir length of 50 m. Besides, a strategy is suggested to improve the oil recovery efficiency of the present in Situ MEOR approach by characterizing the reservoir for its pore size distribution index, and formation fluids (oil and water) for their viscosity ratios and crude oil API gravities, under nonisothermal and substrate inhibition conditions.

Extraction of the indigenous crude oil dissolved biosurfactants and their potential in enhanced oil recovery

The presence of indigenous microorganisms in the petroleum reservoirs with the capability of biosurfactants production implies the existence of significant amounts of biosurfactants dissolved in the reservoir crude oil. The extraction of these biosurfactants to the aqueous phase can be considered as a promising microbial enhanced oil recovery process in a lower cost without the common limitations and risks related to the microbial systems. Ethylenediamine (EDA) was used to extract the crude oil dissolved biosurfactants (as anionic surfactants) of a crude oil sample to the aqueous phase and form a cat-ionic surfactant complex. The biosurfactant was isolated from the crude oil and preliminarily characterized which was capable of reducing the surface tension to 48 mN/m. Various concentrations of EDA were utilized to extract the crude oil biosurfactants and their effectiveness on the oil recovery was studied in a glass micro-model. Results indicated that an incremental 22 % oil production was obtained by flooding the 10 mM EDA solution. The incremental oil production was related to the formation of the cat-ionic complex surfactant which believed to cause a significant IFT reduction and simultaneously, have a higher efficiency in the wettability alteration than the anionic biosurfactants. It can be concluded that the extraction of the indigenous biosurfactant content of the crude oil and their interaction by EDA can be considered as a low-cost low-risk potential to the enhanced oil recovery processes.

Microbe-induced fluid viscosity variation: field-scale simulation, sensitivity and geological uncertainty

This study is intended to expand the scope of microbial enhanced oil recovery (MEOR) simulation studies from 1D to field scale focussing on fluid viscosity variation and heterogeneity that lacks in most MEOR studies. Hence, we developed a model that incorporates: (1) reservoir simulation of microbe-induced oil viscosity reduction and (2) field-scale simulation and robust geological uncertainty workflow considering the influence of well placement. Sequential Gaussian simulation, co-kriging and artificial neural network were used for the petrophysical modelling prior to field-scale modelling. As per this study, the water viscosity increased from 0.5 to 1.72 cP after the microbe growth and increased biomass/biofilm. Also, we investigated the effect of the various component compositions and reaction frequencies on the oil viscosity and possibly oil recovery. For instance, the fraction of the initial CO2 in the oil phase (originally in the reservoir) was varied from 0.000148 to 0.005 to promote the reactions, and more light components were produced. It can be observed that the viscosity of oil reduced considerably after 90 days of MEOR operation from an initial 7.1–7.07 cP and 6.40 cP, respectively. Also, assessing the pre- and post-MEOR oil production rate, we witnessed two main typical MEOR field responses: sweeping effect and radial colonization occurring at the start and tail end of the MEOR process, respectively. MEOR oil recovery factors varied from 28.2 to 44.9% OOIP for the various 200 realizations. Since the well placement was the same for all realizations, the difference in the permeability distribution amongst the realizations affected the microbes’ transport and subsequent interaction with nutrient during injection and transport.