MEOR Process Research Articles

Laboratory Determination of Productivity of Bomu Oil Field (Oml 11 as Case Study) Using MEOR Process and Calcium Oxide Nanoparticles

The need for petroleum products in the world is increasing daily, this product can only be gotten from the refining of crude oil a naturally occurring mineral resource which is produced by degradation of organic materials. This crude is gotten from several wells drilled for the sole purpose of the production of this mineral resource but this wells are being shut-down and abandoned because of the decrease in the well’s productivity which causes losses to the operators and poor finances for the petroleum industry. Therefore, the need to increase the recovery of a well is been considered, these methods are called enhanced oil recovery method. These methods include Gas injection method, Steam Injection method, Chemical injection method (chemicals such as surfactants, polymers etc) Microbial method and the use of nanoparticles as additives to help increase the recovery process. The type of enhanced oil recovery used in this work is the microbial enhanced oil recovery, this method makes use of biosurfactants which can also be referred to as microbe surfactants. The biosurfactants are gotten from microorganism they act as surfactants which reduces the interfacial tension between the molecules of the substance and the interface, this biosurfactants can be used for many industrial purposes which includes bioremediation, oil recovery etc. Nanoparticles are also another aspect of the recent technology which can increase the recovery of our well providing more crude and finance for the petroleum industry. This work shows how biosurfactants and nanoparticles when used together can increase oil recovery. The ever-rising global demand for energy and the issue of large volumes of unrecovered oil after primary and secondary oil production operations are driving the development and/or advancement of enhanced oil recovery (EOR) techniques. Conventional EOR processes include thermal, immiscible and miscible gas injection, chemical, and microbial enhanced oil recovery

Bacillus subtilis‐based microbial enhanced oil recovery (MEOR) in polymer microfluidic chip

AbstractMicrobial 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.

Батыс Қазақстан кен орындарының мұнайпласт суларынан оқшауланған микроорганизмдердің таксономиялық әртүрлілігін шетелдік мұнай кен орындарымен салыстыру

The article describes a variety of microorganisms, isolated from oil reservoir waters of different oilfields that are main objects in studying the micrоbiаl еnhаnсеd оil rесоvеrу (МЕОR) methods. Microorganisms can generate a number of potentially useful metabolites (biomass, biosurfactants, bioacid, biosolvents, biopolymer, biogas) for oil recovery. These metabolites help to reduce the oil’s viscosity and the interfacial friction between oil and water as a surfactant, increase its porosity and permeability. The article discusses the taxonomic biodiversity of microorganisms of oil-formation waters of three active wells of the “Zhetybai”, “Kulsary”, and “Akingen” fields and from different oil deposits across the world for several years. The significance of oil microorganisms, their research, the importance of MEOR processes, comparison of oil microbes between international and Western Kazakhstan oil reserves and future of these microorganisms are widely studied. The article provides information on microorganisms, such as Bacillus sp., Pseudomonas sp., that are more immune to adverse shifts in environmental changes. These genera produce surfactants, gases, alcohols, acids, and biopolymers. The similarity of the taxonomic biodiversity of oil microorganisms of oilfields in Western Kazakhstan and their prospects, as well as the use of microorganisms from the distant countries’ oilfields in the MEOR processes are analyzed.

A Review on Biosurfactant Applications in the Petroleum Industry

The inadequacy of worldwide fossil fuel resources, combined with increasing energy demands, encourages global attention to either using alternative energy resources or improving the recovery factor and produce larger quantities from present reservoirs. Among all enhanced oil recovery (EOR) methods, surfactant injection is a well-known technique that reduces the interfacial tension (IFT) between oil and water and increases oil production. Despite numerous advantages of using surfactants, there are also a few obstacles like environmental impacts, high cost, effect on humans and other organisms due to toxicological potential, and availability from nonrenewable resources. Biosurfactants are microbial surface-active agents that decrease the surface tension (ST) of a liquid phase and the IFT of two diverse phases. They are biotechnological products of high value owing to their widespread applications, low toxicity, relatively easy preparation, and specific performance, applied in different industries like organic chemicals and fertilizers, agrochemicals, metallurgy and mining, cosmetics, foods, medical and pharmaceuticals, beverages, environmental management, and petroleum and petrochemical applications in emulsifying and demulsifying wetting agents, detergent spreading and foaming agents, and functional food ingredients. Biosurfactants are synthesized by microbes; therefore, various genetic diversities of microorganisms provide the considerable capability to produce new types of biosurfactants, which can develop EOR technology. Biosurfactants are classified into ex situ and in situ MEOR processes. The genera Pseudomonas, Bacillus, Sphingomonas, and Actinobacteria are the foremost biosurfactant-producing bacteria. This paper reviews relevant reports and results from various presented papers by researchers and companies on applications of microorganisms and biosurfactant technology with specific emphasis on EOR and MEOR processes, based on recently published articles since 2010 until now.

Numerical Modeling on the Influence of Effective Porosity, Microbial Kinetics, and Operational Parameters on Enhanced Oil Recovery by Microbial Flooding Within a Sandstone Formation

Summary During the implementation of a microbial-enhanced-oil-recovery (EOR) (MEOR) technique in a sandstone formation, various reservoir physicochemical, microbial kinetic, and operational parameters play major roles in governing the efficiency of crude-oil recovery from a hydrocarbon reservoir. The present study numerically investigates the sensitivity of sandstone formation effective porosity; different injected strains of the species Bacillus under optimal metabolic conditions and possessing distinct values of maximum microbial-specific-growth rate, Monod saturation constant, and yield coefficient; and crucial operational parameters on biomass and biosurfactant production and their effects on microscopic oil-displacement efficiency within the sandstone reservoir, along with prompting modifications in rock physicochemical properties. A black-oil biochemical multispecies reactive transport model in porous sandstone media is developed by coupling the kinetic model with the corresponding transport model involving microbial sorption. The governing equations involve coupled transport of nutrients and microbes by dispersion and convection, growth and decay rates of microbes, chemotaxis, nutrient consumption, and deposition of microbes and nutrients on rock-grain surfaces caused by reversible/irreversible sorption. Coupled empirical equations are used to estimate biosurfactant production, oil/water-interfacial-tension (IFT) reduction, change in the viscosity of injection fluid, and their effects on oil relative permeability and mobility, and thus a decrease in residual oil saturation within the reservoir. The finite-difference-discretization technique is adopted to solve the governing equations. Results of the present model are found to be numerically stable and match very well, when verified, with the previously published analytical, numerical, and experimental results. The model results suggest that at very low reservoir porosity (approximately 10%), an early breakthrough of nutrients, microbes, and biosurfactant leave insignificant concentrations in their respective fronts, which are insufficient for the recovery of the trapped oil. Also, increase in porosity to approximately 30% and beyond causes loss of nutrients, microbes, and biosurfactant because they undergo higher dispersion during their transport within the reservoir. Thus, sandstone formations possessing an intermediate effective porosity value of approximately 20% significantly enhance the efficiency of the overall MEOR process. Further, it is observed that the nature of microbes and nutrients used for MEOR application affect biosurfactant production, and in turn oil recovery, to a large extent. Those microbial species with far lower Monod-saturation-constant values have high affinity toward their substrates. This phenomenon dramatically increases the rates of nutrient consumption and production of biomass and biosurfactant within a reservoir when suitable substrate compounds are used, irrespective of differences in the yield coefficients of the microbes. Further MEOR simulation studies within a sandstone core exhibited maximum oil displacement and recovery at a run time of 5 hours, injected-microbial concentration of 4.32×10–3 mg/cm3, and maximum specific growth rate of 0.35 hours–1. Bioplugging-induced formation damage negatively affecting the oil-recovery efficiency is also observed with an increase in the process run time. The screened microbe also exhibited the possibility of wettability alteration of sandstone-formation rock from mixed/oil-wet to water-wet. Thus, the present study provides an improved understanding of the combined effects of reservoir porosity, microbial kinetic, and key operational parameters on fundamental MEOR processes, which will better characterize and develop an effective strategy to determine the suitability of an MEOR technique in a typical sandstone reservoir. Moreover, the developed numerical model is easier to implement and produces faster results with relatively lower computational cost, which helps in making a quick decision before applying MEOR processes in the field.

Numerical simulation of impact of biopolymer production and microbial competition between species on performance of MEOR process

In this work we look at MEOR processes including biopolymer production and microbial competition. We have simulated a two-phase system containing of oil, water, nutrients, metabolite (biopolymer) and biofilm using the Matlab Reservoir Simulation Toolbox (MRST) package. Different mechanisms including water viscosity improvement by the action of biopolymer and biofilm formation due to adsorption of bacteria was studied. The effect of microbial competition due to presence of indigenous bacteria on the performance of MEOR process was also studied. Results shows that the presence of biopolymer improves the oil recovery in comparison with pure waterflooding. The biopolymer improves the recovery by creation of a traveling oil bank within the reservoir. Further analysis is performed to evaluate the influence of a high permeability thief zone to the model. The presence of indigenous microbes has been revealed to limit the MEOR displacement efficiency in both MEOR and thief zone simulations.

The role of biodegradable surfactant in microbial enhanced oil recovery

Many aerobic microorganisms can produce bio-surfactants which are capable of effectively reducing interfacial tensions between oil, water and rock. However, there are few publications on the production of bio-surfactants from anaerobic organisms. The combined effect of bio-surfactant, green surfactant and alcohol in the MEOR process, are not well understood yet and require further investigation. This experimental study was conducted to examine the effectiveness of combination of two microbial by-products, bio-surfactant and bio-alcohol, in recovering residual oil within the pores of rock. It also considered whether bio-surfactant capability could be improved by blending it with non-ionic green surfactant. Two formulations of surfactant and co-surfactant mixtures were selected for core-flood experiments based on phase behaviour study and IFT reduction to examine their potential for enhanced oil recovery. In the first formulation, JF-2 bio-surfactant was mixed with butanol; it was found that this formulation did not produce a significant quantity of incremental oil after water flooding. Lastly, a bio-surfactant (anionic) was blended with non-ionic green surfactant alkyl polyglucoside and butanol; this produced about 25% tertiary oil and 64% OIIP.

Microbial enhanced oil recovery using a biosurfactant produced by Bacillus safensis isolated from mangrove microbiota - Part I biosurfactant characterization and oil displacement test

After primary and secondary recovery operations, the majority of the original oil in place remains in the reservoir due to physical and geological limitations. Thus, increasing oil recovery yields and reducing operational costs are major goals of the oil industry and efforts are being made to develop economic methods of enhanced oil recovery. One alternative method is the use of the microbiological enhanced oil recovery method (MEOR), which uses microorganisms or their metabolites, including biosurfactants, to mobilize the oil trapped in reservoirs and increase the oil recovery factor. This study aimed to evaluate the potential of a pumilacidin produced by Bacillus safensis CCMA-560 to increase oil recovery in a laboratory scale MEOR process. This bioactive molecule was previously isolated from a mangrove, increasing its potential to contribute to a more sustainable economy and to the environment. The critical micelle concentration (CMC) of the biosurfactant was determined by surface tension and thermal gravimetric analysis (TGA) was performed to evaluate if its thermal stability is consistent with the average reservoir temperature. Surface and interfacial tension measurements were performed to investigate the interfacial activity behaviors of the biosurfactant with oil and brine. Core flood experiments showed that this biosurfactant has a great potential for chemical EOR flooding applications. The results demonstrated that an alternate injection of a 1.3 CMC biosurfactant solution and 3 wt% brine should be able to permeate through the porous media, migrate to the water/oil interface, reduce the interfacial tension (IFT), and increase the oil recovery factor by 13%. In additional, a core flood experiment was performed to study the impact of this MEOR injection on the rock properties.

Systematic Modeling Approach to Selective Plugging Using In Situ Bacterial Biopolymer Production and Its Potential for Microbial-enhanced Oil Recovery

This study presents a systematic modeling approach for examining the efficiency of the MEOR process based on in situ selective plugging by bacterial biopolymer production and optimization of the nutrient injection strategy to yield the maximum oil recovery. This study focuses on modeling in situ selective plugging by the bacterial biopolymer dextran that is generated by Leuconostoc mesenteroides. Bacterial growth and dextran generation were described by a stoichiometric equation and kinetic reactions using batch model simulation. Based on the parameters for permeability reduction obtained from the sandpack model, the MEOR process was implemented in a pilot-scale system that included a highly permeable thief zone in a low-permeability reservoir. The base MEOR design yielded a 61.5% improvement of the recovery factor compared to that obtained with waterflooding. The parametric simulations revealed that the recovery efficiency was influenced by the amount of dextran, as well as the distribution of dextran, and thus, the injection strategy is critical for controlling the dextran distribution. By incorporating the results from the sensitivity analysis and optimization to determine the optimal design parameters, a 36.7% improvement of the oil recovery was achieved with the optimized MEOR process in comparison with the base case.

Isolation and screening of Bacillus subtilis MJ01 for MEOR application: biosurfactant characterization, production optimization and wetting effect on carbonate surfaces

The bacterial strain MJ01 was isolated from stock tank water of one of the Iranian south oil field production facilities. The 16S rRNA gene of isolate, MJ01, showed 99% similarity to Bacillus subtilis. The results revealed that biosurfactant produced by this strain was lipopeptide-like surfactin based on FTIR analysis. Critical micelle concentration of produced surfactin in distilled water was 0.06 g/l. Wettability study showed that at zero salinity surfactin can change original oil-wet state to water-wet state, but in seawater salinity it cannot modify the wettability significantly. To utilize this biosurfactant in ex situ MEOR process, economical and reservoir engineering technical parameters were considered to introduce a new optimization strategy using the response surface methodology. Comparing the result of this optimization strategy with the previous optimization research works was shown that significant save in use of nutrients is possible by using this medium. Furthermore, using this method leads to less formation damage due to the incompatibility of injecting fluid and formation brine, and less formation damage due to the bioplugging.

Investigating the synergic effects of chemical surfactant (SDBS) and biosurfactant produced by bacterium (Enterobacter cloacae) on IFT reduction and wettability alteration during MEOR process

In the current study, a novel approach which takes into account the effectiveness of both convectional surfactants and biosurfactants was investigated. The biosurfactant produced by Enterobacter cloacae strain was utilized concomitant with conventional surfactant (sodium dodecyl benzene sulfonate (SDBS)) to evaluate its capability to reduce the SDBS adsorption on rock surface (biosurfactant acts as sacrificial agent) or synergistically enhance the effectiveness of the SDBS. In this regard, the wettability alteration and interfacial tension (IFT) measurements and calculation of spreading coefficient were performed considering two different scenarios. In the first scenario, SDBS was added to the incubated bacterial solution medium while in the second case, SDBS was added to the bacterial solution before the incubation stage. Based on the obtained results, it was revealed that the wettability altered from original oil wet towards water wet state using bacterial solution, while the addition of SDBS deteriorated this trend for both scenarios. According to IFT measurements, the first scenario was more effective than the individual solution of bacteria and SDBS as well as the second scenario. In conclusion, the measured spreading coefficient demonstrated that the bacterial solution was a more effective EOR agent in comparison to other studied cases.

Biosurfactant production under diverse conditions by two kinds of biosurfactant-producing bacteria for microbial enhanced oil recovery

Stable growth and efficient production of biosurfactant by functional bacteria in oil reservoirs are indispensable for MEOR process. Biosurfactant production of bacteria has been mainly studied under aerobic conditions, but information on biosurfactant production under diverse conditions is still scarce. Two kinds of common biosurfactant-producing bacteria (Bacillus amyloliquefaciens 702 and Pseudomonas aeruginosa 709) were isolated from production fluid of Xinjiang oil field, China. Biosurfactant production by two strains was investigated under aerobic conditions, anaerobic conditions and high pressure (10 MPa) conditions, respectively. Under aerobic conditions, both B. amyloliquefaciens 702 and P. aeruginosa 709 decreased the surface tension of aerobic culture to lower than 27 mN/m at temperatures (25°C-40 °C), pH values (6.0–9.0) and less than 30 g/l NaCl. Strains 702 and 709 can aerobically produce 1582.4 mg/l and 8237.5 mg/l of biosurfactant. Both two aerobic cultures emulsified crude oil with EI24 values up to 84%. Both biosurfactant produced by strains 702 and 709 are thermo-stable and halo-tolerant. Although both two strains can grow under anaerobic conditions or high pressure conditions, only strain 709 efficiently produced biosurfactant under these conditions. Results of core flooding tests showed that another 7.04% of original crude oil was displaced through in situ production of biosurfactant by strain 709, and 1.10% of original crude oil was recovered by strain 702. Strain P. aeruginosa 709 can efficiently produce biosurfactant under anaerobic and high pressure conditions, so it is more suitable and advantageous for in situ MEOR applications. The feasibility of in situ production of biosurfactant used in oil fields was also discussed.

Numerical modelling of enhanced oil recovery by microbial flooding under non-isothermal conditions

In the present paper an attempt has been made to develop an improved numerical model in order to simulate the oil recovery by microbial flooding under non-isothermal conditions. The proposed model simulates the coupled heat and mass transfer resulting from the mobility of microbes along with its nutrients in a typical petroleum reservoir against the conventional isothermal conditions. The model results have been verified with the existing analytical and experimental results. The present model evaluates the optimum mean fluid velocity in order to achieve the maximum oil displacement under different reservoir temperature conditions. The model also investigates the change in relative permeability of oil and water during microbial flooding within the reservoir under non-isothermal conditions and subsequently estimates the residual oil recovery. The model results suggest that the microscopic oil displacement efficiency increases with the increase in mean fluid velocity and reaches a threshold maximum oil displacement just before the water breakthrough at a relatively lower temperature. In addition, it is observed that the maximum oil displacement efficiency of 82.75% is achieved at a reservoir temperature of 60 °C and at an optimum mean fluid velocity of 1.68 m/day in a sandstone reservoir of length 50 m. • Developed a numerical model to evaluate MEOR process under non-isothermal conditions. • Heat distribution in reservoir impacts microbial growth, viscosity of water and oil. • Transport of nutrients and microbes within reservoir is coupled with Monod kinetics. • Studied the impact of reservoir temperature and mean fluid velocity on K rw , K ro . • Evaluated oil displacement efficiency of MEOR under different reservoir conditions.

Development of a microbial process for the recovery of petroleum oil from depleted reservoirs at 91–96 °C

A consortium of bacteria growing at 91°C and above (optimally at 96°C) was developed for the recovery of crude oil from declining/depleted oil reservoirs having temperature of more than 91°C. PCR-DGGE-Sequencing analysis of 16S rRNA gene fragments of NJS-4 consortium revealed the presence of four strains identified as members of the genus Clostridium. The metabolites produced by NJS-4 consortium included volatile fatty acids, organic acids, surfactants, exopolysaccarides and CO2, which reduced viscosity, emulsified crude oil and increased the pressure that facilitated displacement of emulsified oil towards the surface. NJS-4 enhanced oil recovery by 26.7% and 10.1% in sand pack trials and core flood studies respectively in optimized nutrient medium comprised of sucrose and sodium acetate as carbon/energy source and urea as nitrogen source (pH 7–9, 96°C, and 4% salinity). Nutrient medium for MEOR was constituted using commercial grade cheap nutrients to improve the economic viability of MEOR process.

Modification of rock/fluid and fluid/fluid interfaces during MEOR processes, using two biosurfactant producing strains of Bacillus stearothermophilus SUCPM#14 and Enterobacter cloacae: A mechanistic study

During any microbial enhanced oil recovery process, both cells and the metabolic products of bacteria govern the tertiary oil recovery efficiency. However, very accurate examination is needed to find the functionality of these tiny creatures at different reservoir conditions. In this regard, the effect of cell structure on ultimate microbial recovery efficiency which is the most dominant mechanism based on the microorganism types (gram-negative or gram-positive) was systematically investigated. At the first stage, possible different active mechanisms using Bacillus stearothermophilus SUCPM#14 strain were tested using specially designed injection protocol, in situ and ex situ core flooding experiments, interfacial tension, viscosity, pH and Amott wettability index measurements. At the second stage, comparing functionality of B. stearothermophilus SUCPM#14 (a gram-positive type) with the previously examined strain namely Enterobacter cloacae as a gram-negative type, proposed this hypothesis that the cell structure significantly affects the interfacial behaviors. New designed protocols were utilized to check the individual effects of cells, bioproducts and interaction of these together on the oil/water and also fluids/rock interfaces. The final results showed that the cells of B. stearothermophilus SUCPM#14 adhere more into the oil/water interface compared to E. cloacae and change its rheological properties; e.g. its elastic properties which affect the ultimate microbial oil recovery efficiency. Eventually, contradicting results revealed that biosurfactant produced by E. cloacae was able to considerably reduce the interfacial tension and alter the wettability of the rock (to neutral conditions) while biosurfactant produced by B. stearothermophilus SUCPM#14 was not very effective.

Production and Characterization of Bioemulsifiers by Thermotolerant Bacteria for Enhanced Oil Recovery Potential

Three bacterial strains were isolated from oil contaminated soil samples in Yumen oilfield of China and selected due to their capacity of growing under extreme conditions and production of bioemulsifier. The isolates were identified as Brevibacillus sp. XS1, Geobacillus sp. XS2 and Geobacillus sp. XS3 according to 16S rDNA sequence and physiological methods, respectively. The isolates XS1, XS2 and XS3 were thermotolerant with the optimum growth temperature of 50 °C, 60 °C and 55 °C, respectively. All the three isolates were able to produce bioemulsifiers which had little effect on surface tension reduction. The bioemusifiers produced by the three isolates were purified with a production yield of 2.98g/L, 4.24g/L and 3.82 g/L, respectively. The bioemulsifiers were identified as anionic heteropolysaccharides by FTIR analysis and their average molecular weight and polydispersity were investigated by GPC method. The bioemulsifiers produced by Geobacillus sp. XS2 and XS3 exhibited a perfect stability over various temperature (up to 100 °C), pH (range from 2.0 to 12.0) and salinity (up to 30.0% of NaCl concentration) and were considered to be ideal candidates in MEOR process.

Production and Characterization of Bioemulsifiers by Thermotolerant Bacteria for Enhanced Oil Recovery Potential

Three bacterial strains were isolated from oil contaminated soil samples in Yumen oilfield of China and selected due to their capacity of growing under extreme conditions and production of bioemulsifier. The isolates were identified as Brevibacillus sp. XS1, Geobacillus sp. XS2 and Geobacillus sp. XS3 according to 16S rDNA sequence and physiological methods, respectively. The isolates XS1, XS2 and XS3 were thermotolerant with the optimum growth temperature of 50 °C, 60 °C and 55 °C, respectively. All the three isolates were able to produce bioemulsifiers which had little effect on surface tension reduction. The bioemusifiers produced by the three isolates were purified with a production yield of 2.98g/L, 4.24g/L and 3.82 g/L, respectively. The bioemulsifiers were identified as anionic heteropolysaccharides by FTIR analysis and their average molecular weight and polydispersity were investigated by GPC method. The bioemulsifiers produced by Geobacillus sp. XS2 and XS3 exhibited a perfect stability over various temperature (up to 100 °C), pH (range from 2.0 to 12.0) and salinity (up to 30.0% of NaCl concentration) and were considered to be ideal candidates in MEOR process.

Model Development for MEOR Process in Conventional Non‐Fractured Reservoirs and Investigation of Physico‐Chemical Parameter Effects

AbstractA three‐dimensional multi‐component transport model in a two‐phase oil‐water system was developed. The model includes separated terms to account for the dispersion, convection, injection, growth and death of microbes, and accumulation. For the first time, effects of both wettability alteration of reservoir rock from oil wet to water wet and reduction in interfacial tension (IFT) simultaneously on relative permeability and capillary pressure curves were included in a MEOR simulation model. Transport equations were considered for the bacteria, nutrients, and metabolite (bio‐surfactant) in the matrix, reduced interfacial tension on phase trapping, surfactant and polymer adsorption, and effect of polymer viscosity on mobility of the aqueous phase. The model was used to simulate effects of physico‐chemical parameters, namely flooding time schedules, washing water flowrate, substrate concentration, permeability, polymer and salinity concentration on Original Oil In Place (OOIP) in a hypothetical reservoir.

水溶性ポリマー生産微生物を用いたＭＥＯＲの数値実験

Our group has carried out the various studies and experiments on MEOR process with the microbe producing water-soluble polymer. Based on these efforts, the basic performance and mechanism in this process were well simulated by computation experiment in the previous paper.In this paper, our group carried out the case studies of this process using the computation experiments and suggested the important conditions and its sensitivity of the effect.First, the effect of reservoir conditions was estimated by changing permeability distribution, oil viscosity and oil saturation. The ratio of the enhanced oil recovery by this process was high at the all conditions of reservoir. It should be noted that this process was effective in any types of reservoir without restrictions of permeability distribution, oil viscosity variety. It was shown that the application of this process in the earlier stage of development was more effective because oil recovery was accelerated in the earlier stage by increase of oil saturation.Next, the effect of cultivation conditions was estimated by changing nutrient concentration, shut-in time for incubation and fluid property. The ratio of the enhanced oil recovery became higher by increase of nutrient concentration, but they had not proportionality relation. Therefore, it is necessary to optimize nutrient concentration for target reservoir by estimating the economical efficiency. It was suggested that taking shut-in at least for 2 days was one of necessary procedure for higher enhanced oil recovery.Third, the effect of injection conditions was estimated by changing injection volume, rate of microbe, nutrient solution and injection cycle of the solution and water. It was shown that those conditions must be optimized by considering economical efficiency for target reservoir.In conclusion, it was suggested that the enhanced oil recovery by this MEOR process can be optimized by selecting suitable conditions to reservoir characteristics and by controlling conditions of cultivation and injection.

水溶性ポリマー生産微生物を用いたＭＥＯＲにおける油層内挙動と石油増進回収機構に関するシミュレーション研究

Our research group has carried out experimental studies to analyze the performance and the mechanism of MEOR with TU-15A, a microbe that produces water-soluble polymer. In the previous study, a mathematical model for this MEOR was developed, including almost all important phenomena such as growth and death of microbe, consumption of nutrient, production of water-soluble polymer, increase of water viscosity and the flow of reservoir fluids.In this study, the validity of the MEOR simulation model was firstly examined by comparison between experimental and computed results. The results of the numerical simulation agreed with the experimental results in terms of oil recovery, injection pressure, oil cut and flow profile of injection water.Next, numerical simulation was carried out to analyze the performance and mechanism of this MEOR process for five-spot pattern flooding. The procedure and the conditions used are as follows.Step 1: Conduct water flooding until water cut becomes 90%.Step 2: Inject microbe and nutrient solution into reservoir up to 0.1 PV.Step 3: Shut-in and wait for cultivation in the reservoir for 10 days.Step 4: Conduct postflash until water cut becomes 95%.The quantitative changes of microbe, nutrient, water viscosity and oil saturation were analyzed. Regarding the alteration of flow pattern in the reservoir, it was found that (1) the water-soluble polymer produced by the microbe flowed into the main flow channel along the shortest way between the injection well and the production well and water viscosity there increased, (2) subsequently more uniform flow profile of injected water for oil recovery was established, and (3) then the residual oil was mobilized to the production well. The more than 10% additional oil recovery was obtained in the early phase of postflash in this MEOR process compared with waterflooding.