Research for Microbial Conversion of Residual Oil into Methane in Depleted Oil Fields to Develop New EOR Process

Methane is a clean-burning fuel that is the main component of natural gas. We have attempted to develop a methane-producing system using indigenous microbes in depleted oil fields. In particular, we aim to combine a microbial conversion of the residual oil into methane with the geological sequestration of carbon dioxide: First, hydrogen-producing bacteria are harnessed to produce hydrogen from residual petroleum components in the depleted oil reservoir. Next, methane-producing microbes (methanogens) utilize the hydrogen and carbon dioxide, which is injected for geological sequestration, to generate methane. Resulting methane is therefore a carbon-neutral fuel. As the first step, we successfully isolated multiple hydrogen- and methane-producing microbes (10 hydrogen-producing bacteria and 4 methanogens) from depleted oil fields in Japan. Strikingly, our analysis of inoculums incubated under high temperature and high pressure, the condition similar to native conditions inside of petroleum reservoirs, revealed that indigenous microbes in the reservoir brine are capable of generating methane by utilizing crude oil and carbon dioxide. Consumption/production rate of gases (methane, carbon dioxide) and acetic acid indicated that the methane production under reservoir conditions is likely mediated through two pathways; the aceticlastic (acetic-acid utilizing) and the hydrogenotrophic (hydrogen and carbondioxide utilizing) pathways. Furthermore, by analyzing methane-producing ability of isolated microbes, we found that the syntrophic cooperation between hydrogen-producing bacteria and methanogens is critical for the methane production under the resavoir condition. We are currently determining optimal combination(s) of these microbes to achieve an efficient methane production in the depleted oil field. Our next step will be to establish a method to enhance methanogenic activity of the microbes as well as an effective methanogenesis in porous media, the condition inside of actual reservoirs (porous rock formations). Ultimately, our endeavor will enable a sustainable carbon-cycling system that converts residual oil and stored carbon dioxide in depleted oil fields into environmentally friendly bio-methane.

Inpex and Chugai Technos have been working since 2006 to study methane-producing technology using microbes inhabiting depleted oil fields. The concept and mechanism of microbial methane conversion are depicted as follows.First, hydrogen producing microbes (bacteria) prompt to produce hydrogen from residual petroleum components in the depleted reservoir. Next, methane-producing microbes (methanogens) are concerned in generating methane from the hydrogen and carbon dioxide injected for geological sequestration.The research team in Inpex and Chugai Technos has successfully isolated samples of hydrogen- and methane-producing microbes from the depleted oil fields in Japan (10 hydrogen producing thermophilic bacteria and 4 methane producing thermophilic archaea). It was confirmed that continuous methane production took place using indigenous microbes in the reservoir brine and crude oil as a carbon source with 10 mol% of CO2.Produced gas (methane, carbon dioxide) and concentration of acetic acid indicate that there are 2 reaction pathways from oil to methane. One is the acetoclastic methane producing pathway, another is hydrogentrophic methane producing pathway.Furthermore, from the result of methane producing experiments using isolated microbes, we found there was some syntrophic cooperation between hydrogen producing bacteria and methanogen (methane producing archaea). We must investigate the suitable combination of these microbes in order to get an effective methane production.The next step will be to evaluate the way to enhance the capability of methane-producing microbes and to identify an effective and efficient process of producing methane in the actual reservoir (porous media) condition.If successful, it will be a big step toward building a carbon cycling system that converts residual oil in depleted oil fields into environmentally friendly methane.

Research study has been carried out to investigate the possibility of conversion of residual oil to methane using microbes inhabiting subsurface depleted oil reservoirs. We call the above concept "Unrecoverable Liquid Fuels to Recoverable Gaseous Fuels (ULTRG)" technique. This technique supposes microbial conversion process of crude oil into methane, and the mechanism is estimated as follows. First, hydrocarbon degradation microbes (so called bacteria) are utilized to produce hydrogen and organic acid such as acetate from residual oil that could not be recovered by primary and/or secondary recovery process in matured oil field. Next, methane-producing microbes (so-called methanogens) are used to generate methane from the produced acetate, or hydrogen and carbon dioxide. The reactions of microbial conversion of crude oil (assuming as alkanes) to methane are estimated as follows (Maeda et al., 2010). Acetic acid producing reaction from alkanes CnH2n+2+nH2O→n/2CH3COOH+(n+1) H2 Hydrogen producing reaction from acetate CH3COOH+2 H2O→4 H2+2CO2 Methane producing reaction from acetate CH3COOH→CH4+CO2 Methane producing reaction from hydrogen and carbon dioxide CO2+4 H2→CH4+2 H2O Fluid samples oil and formation water produced from oil and gas fields in Japan were collected and analyzed in order to clarify the existence and survivability of indigenous hydrogen- and methane-producing anaerobes under reservoir conditions. It has not been clarified that crude oil degradation can occur in subsurface oil reservoirs. However, our recent incubation experiment has successfully observed methanogenic crude oil degradation by using subsurface indigenous microbes mimicking the certain reservoir condition as a target of field application. Various culture incubation experiments revealed that methane production occurred by using indigenous microbes inhabiting the reservoir brine, and some nutrient additives accelerated the methane production rate and volume. Further, culture incubation experiments were conducted using artifact-free homogeneous sand grains mimicking porous environments as subsurface oil reservoirs. The porous environment significantly increased microbial activity of methane production, and the subsequent subcultures also continued to produce methane. Stable carbon isotope tracer method was used to clarify the degradation of hydrocarbon compositions. The degradation was judged as variation between the original and post-incubated oils. After the incubation, Scanning Electron Microscope (SEM) observations was observed for the microbes attached on the sand grain, in order to estimate how such porous environment accelerates microbial activities of hydrocarbon degradation and conversion to methane. Furthermore, metagenome analysis will be planned to conduct to investigate the microbial reaction and related microorganisms. In this paper, we are focusing on crude oil biodegradation degree to evaluate the existence of microbes which are involved in the reaction of crude oil degradation and the necessity of nutrients to enhance such reaction. It will be a worth to establishment the ULTRG because this technique will be a big step toward building an innovative microbial methane conversion system from remaining unrecoverable oil.

We developed methods and technology to identify oil and gas fields that are likely to support the restoration of methane deposits, and identified the main characteristics of microbes inhabiting depleted oil and gas fields. To evaluate the potential for microorganisms to inhabit oil and gas fields in Japan, we investigated the existence of methane-producing archaea (MPA) and hydrogen-producing bacteria (HPB) using PCR-DGGE (Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis) analysis. Reservoir brine from Yabase oil field (Akita Pref., Japan), which was incubated under strictly anaerobic conditions at 50°C, actively produced methane, indicating that Yabase oil field is a suitable site for methane generation. Moreover, analysis of the enrichment culture revealed that it is possible for indigenous anaerobes inhabiting an oil field to generate methane from oil components. Additionally, findings established a methanogenic pathway composed of MPA such as Methanoculleus sp., Methanothermobacter thermoautotrophicus, and Methanosaeta sp. and hydrocarbon-degrading hydrogen-producing bacteria (HD-HPB) related to Thermotoga sp., Petrotoga sp. and Clostridiaceae str. These results strongly suggest that Yabase oil field has the technological potential for the microbial restoration of methane.

Many oil reservoirs have passed their production life and oil production is reducing. These fields may be termed as depleted oil fields. Depending on the type of reservoir, a great portion of initial oil in place (30-80%) is still left as the residual oil (Bauer et al. 2022). Current climate policies which are against carbon dioxide (CO2) producing fuels make it less and less attractive to produce this remaining oil by employing various enhanced oil recovery technologies until abandonment. These reservoirs in particular may be well-suited for alternative forms of production or for the use of new fuels for field rejuvenation since there is typically sufficient infrastructure in the form of platforms, pipeline networks, and wells, and there is sufficient understanding regarding the subsurface behavior (Veshareh et al. 2022). Hydrogen, as one of the green and sustainable fuels, can be produced under subsurface conditions (Nicole et.al, 2022; Bhutto et.al, 2013; Hajdo et.al, 1985; Veshareh et.al, 2022). Especially, hydrogen production in oil and gas reservoirs has been extensively researched (Kapadia 2009, 2013; Murthy et. al. 2014; Strem et al. 2021; Wang & Gates, 2020; Bauer et al. 2022). Two main techniques can be applied to produce hydrogen from depleted oil reservoirs, namely, 1) Thermal hydrogen production by in-situ combustion; 2) microbiological hydrogen production by dark fermentation. Since microbiological hydrogen production requires less energy, it is a very promising method. Using microorganisms that use a carbon source as a substrate, hydrogen can be produced (Sivaramakrishnan et al. 2021). This is known as biohydrogen. Depending on the substrate and the microbe, biohydrogen can be produced by a variety of methods, such as bio-photolysis, indirect photolysis, dark fermentation, photo fermentation, and microbial electrolysis. Because dark fermentation has the potential to produce more hydrogen, with simpler operating restrictions, and can improve pH conditions, this method of hydrogen production has garnered a lot of attention (Supriya, 2019; Sivaramakrishnan et al. 2021). Many other techniques for pretreatment, including thermochemical, ultrasound, thermal, alkali/acid, chemo mechanical and heat shock have been used for hydrogen generation. However, these techniques either are challenging to deploy especially in offshore settings in Malaysia, difficult to use, or produce hazardous chemicals that are harmful for the environment. Therefore, there is a strong interest in the biological production of hydrogen from reservoirs by manipulating the growth of existing hydrogen-producing microbes. This manipulation involves selecting specific substrates or nutrients that may already be present in the fluids. Recognizing the interconnected nature of biological processes with thermal, hydraulic, mechanical, and chemical processes has led to an enhanced comprehension of the importance of hydrogen-metabolizing microorganisms in subsurface environments (Lu et al. 2011). Microorganisms can be found in a variety of environments, microbial populations in samples from various oil and gas fields have been extensively reported in subsurface environments (Silva et al. 2013). Native microbes play an important role in the deep biosphere and can survive in these oil reservoirs’ extreme conditions. Oil exploration by humans has impacted the microbial dynamics in these environments. According to a recent study, members of the families Thermotogales, Clostridia, Deferribacteres, and Proteobacteria dominated the microbial community composition in offshore oil fields that used nitrate-altered seawater as injection fluid (Vigneron et al. 2017). The fermentation and degradation of detrital organic matter, acetogenesis and the degradation of aromatic hydrocarbons, and nitrate reduction and oxidative processes such as the oxidation of hydrogen sulphide or sulphur are the primary metabolic processes of these populations. Oil production causes significant systematic changes in microbial communities Vigneron et al. (2017).

CO2 sequestration into depleted oil reservoir has been expected as a method of reducing CO2 emission. Moreover, the authors focus on in-situ microbial conversion process of carbon dioxide into methane by hydrogenotrophic methanogens that inhabit oil reservoir universally. It is important for this process how to supply hydrogenotrophic methanogens with hydrogen for their methane production in reservoir. This study is aimed at searching for the oil-degrading and hydrogen-producing thermophilic bacteria (ODHPTB) which can produce hydrogen from oil in reservoir brine. Reservoir brine was extracted from 10 producing wells in Yabase oilfield in Japan. Indigenous bacteria in brine samples were incubated with sterilized oil under anaerobic conditions (10% CO2 balance N2) at 50°C and/or 75°C. Both the production of hydrogen and methane and the consumption of carbon dioxide were observed in almost all culture solutions after 2 months incubation. The maximum rate of hydrogen production was 20.9 Nml/L-medium/day. These culture solution and raw brine were inoculated into nutrient agar medium and incubated under anaerobic conditions at 50°C and 75°C. Microbial single colonies formed in the nutrient agar medium after 2 weeks incubation were picked and inoculated into sterilized brine including sterilized oil as a hydrogen source. More than 40 strains were isolated and incubated in the brine medium and 24 strains were observed to produce hydrogen from oil after 1 month incubation. The maximum rate of hydrogen production was 1.0 Nml/L-medium/day. These results show that the in-situ microbial conversion process of carbon dioxide and residual oil into methane using ODHPTB and hydrogenotrophic methanogens is promising. Moreover, the most talented ODHPTB that was isolated in this study can be injected into reservoir in order to stimulate the conversion of carbon dioxide into methane.

The purpose of this paper is to investigate the effects of phase behavior on the sequestration CO2 of in depleted gas reservoirs (dry gas, wet gas and retrograde gas). Carbon dioxide sequestration in depleted and abandoned gas reservoirs can accomplish two important objectives. Firstly, it could be important part of present climate control initiative to reduce the concentration of carbon dioxide in the atmosphere. Secondly, it could be instrumental to enhance gas and condensate recovery. Using the pressure-temperature diagrams and two phase flash calculations, the phase behavior of natural gas-carbon dioxide mixtures were analyzed to provide enlightenment on the sequestration process. From analysis of simulated results, it was found that carbon dioxide exhibited a drying effect on wet and retrograde gas mixtures and a wetting effect on dry gas. The results for retrograde gas condensate depended on the composition of reservoir fluids at abandonment conditions. The main difference being the liquid volume present with increasing pressure and carbon dioxide concentration. This influenced the volume of condensate vaporized with addition of carbon dioxide. It was also determined that carbon dioxide lowers the compressibility factor of all gas types. These results are favorable for carbon dioxide sequestration because decreasing compressibility factors represents increasing storage capacity.

Effects of simultaneous hydrogen enrichment and carbon dioxide dilution of fuel on soot formation in an axisymmetric coflow laminar ethylene/air diffusion flame

Sequestration of carbon dioxide (CO2) in depleted oil reservoir is a strategy currently being considered to reduce the amount of CO2 in the atmosphere. However, a better understanding and prediction of the geologic processes that control CO2 injection in porous geologic media is necessary before depleted oil fields can become a safe and economical sequestration option. This paper provides new experimental and modeling results from a Department of Energy's (DOE) National Energy Technology Laboratory (NETL) sponsored CO2 sequestration project investigating these issues. Geologic modeling and numerical flow simulations are used to study the feasibility of injection into porous media. Interactions between injected CO2, reservoir fluids and reservoir rock are taken into account, including CO2 dissolution in water and water reaction with reservoir rock. These results are helping to design geophysical monitoring studies to track the injected plume. Laboratory tests and reaction path simulations were also used to investigate the fate of injected CO2 with reservoir fluids and minerals during extended static tests with reservoir core and brines. Results may help identify long-term geochemical processes that will affect sequestration.

The process of carbonaceous materials gasification is especially relevant in Russia, where the volume of coal waste exceeds 120 million tons. A gasification installation for carbon-containing waste operating in the fixed-bed mode has been developed. Experiments on gasification of fine coal fraction samples (1–2 mm) were carried out using preheated air, a steam-air mixture, and air with added carbon dioxide as gasifying agents. The work used the methods of differential scanning calorimetry, thermogravimetric analysis, and chromatographic analysis. Additions of water vapor and carbon dioxide made it possible to increase the heat of combustion and increase the gasification efficiency to 54%. The operating mode of the gas generator was determined, ensuring the production of synthesis gas with a calorific value of 3.6 MJ/nm3. It is shown that the highest efficiency of gas generation is achieved in the steam-air gasification mode with the addition of water vapor in the amount of 0.1 kg per 1 kg of coal and with the use of air as a gasifying agent with the addition of carbon dioxide in a volume ratio of 100:5. It is established that an increase in the addition of water vapor and carbon dioxide above the optimal amounts leads to a decrease in the efficiency of the gasification process. The process can use waste from various industries, including oil sludge, which determines its significance for the effective management of carbon-containing waste and for achieving broader environmental and economic goals.

As potential CO2 geological storage site in CCS, utilization of depleted oil/gas reservoirs and aquifer has been proposed. The long-term aim of this research is to establish a biotechnological system to microbiologically convert geologically stored CO2 into methane. Our recent study revealed that methanogen and exoelectrogen inhabiting subsurface reservoir are involved in the recently discovered bioelectrochemical reaction called electromethanogenesis (CO2 + 8H++ 8e− → CH4 + 2H2O). In this reaction, methanogen receives proton from reservoir brine and electron from a solid electrode. As a result, reduces CO2 into methane. Required electricity for the methane conversion can be obtained from renewable energy sources such as wind or photovoltaic power generations. Single-chambered electromethanogenic reactors were used for an evaluation. The reactors were inoculated with reservoir brine anaerobically collected from Yabase oil field in Japan. Each reactor headspace was filled with mixed gases of N2/CO2 (80/20). The reactors were incubated at 55°C with an applied voltage of 0.75 V. The reactors produced methane at a rate of 386mmol/day m−2. The current-methane conversion efficiency was almost 100%. On the other hand, no significant methane production was detected in the reactors without applied voltage. To investigate the mechanism of electromethanogenic reaction, the phylogenetic diversity of the microbes on the cathode was analyzed. The result shows, as for archaea, methanogen closely related to Methanothermobacter thermoautotrophicus dominated. On the other hand, as for bacteria, Thermincola ferriacetica, one of the exoelectrogen, was the dominant spices. Our experimental research demonstrated for the first time that the possibility of bioelectrochemical methane conversion of carbon dioxide by utilizing microbes indigenous to depleted oil fields. The final goal of this research is to establish the "Subsurface Methane Regeneration" system, combining CCS and biotechnology, in which geologically-stored CO2 is converted into CH4 by bio-electrochemical process called "Electromethanogenesis".

Effect of cross airflow on the flame geometrical characteristics and flame radiation fraction of ethylene jet fires with carbon dioxide addition

The technology of enhanced oil recovery based on reservoir microflora activation through periodic activation of the injected water with mineral salts of nitrogen and phosphorus added to it, was developed. As a result, intensification of microorganisms takes place. The microorganisms create such oil displacing products as CO2, CH4, fatty acids, alcohols, surfactants and etc. The method was tested at 7 pilot areas of oil fields in different regions of the country. It allowed to recover 70 thousand tonnes of additional oil.

Hydrogenation of 4-t-butylphenol over an activated carbon-supported rhodium catalyst in carbon dioxide solvent was analyzed based on phase observation with a view cell and calculations of the solubility of 4-t-butylphenol using the Peng-Robinson equation of state as a function of carbon dioxide pressure. The reaction experiments showed that the initial reaction rate of 4-t-butylphenol at 313 K under 2 MPa of hydrogen pressure was increased by the addition of carbon dioxide, especially above a total pressure of 11 MPa. Direct visual observation showed that the solubility of 4-t-butylphenol increased with higher carbon dioxide pressure. The calculations based on the Peng-Robinson equation of state also showed that the solubility of 4-t-butylphenol in the 4-t-butylphenol–carbon dioxide–hydrogen (2 MPa) system at 313 K significantly increased by addition of carbon dioxide above a total pressure of 11 MPa. We concluded that the increase in the hydrogenation rates was caused by the increased concentration of 4-t-butylphenol substrate in the carbon dioxide solvent.

CO2 sequestration into a depleted oil reservoir has been expected to be a method of reducing the CO2 emission. We focus on the in-situ microbial conversion of CO2 into CH4 by hydrogenotrophic methanogens that inhabit oil reservoirs universally. It is important for this conversion process to accelerate the supply of H2 for the CH4 production by methanogens in reservoirs. This study aims to search for oil-degrading and H2-producing thermophilic bacteria (ODHPTB) that can produce H2 from oil in reservoir brine.Reservoir brine was extracted from 10 producing wells in Yabase Oilfield in Japan. Indigenous bacteria in brine were incubated with sterilized oil under anaerobic conditions (10% CO2 and 90% N2) at 50°C and/or 75°C. Both the production of H2, CH4, and the consumption of CO2 were observed in almost all culture systems after 2 months incubation. The maximum production of H2 was 1267 Nml/l-med. for 4 months incubation. Petrotoga sp. and Thermotoga sp. which were reported as ODHPTB were detected as dominant bacteria from each enrichment culture solution by gene analysis.These culture solutions and raw brine were inoculated into nutrient agar medium and incubated under anaerobic conditions at 50°C and/or 75°C. Microbial single colonies which were formed in the nutrient agar medium after 2 weeks incubation were picked and inoculated into sterilized brine including sterilized oil as sole hydrogen source. More than 38 strains were isolated and incubated in the brine medium, and then producing hydrogen from oil were observed from 38 strains after 1 month incubation. The maximum production of H2 was 26 Nml/l-med. for 3 months incubation.These results show the in-situ microbial conversion of CO2 and residual oil into CH4 using ODHPTB and hydrogenotrophic methanogens is promising. Moreover, the valuable characteristics of ODHPTB isolated in this study, made it suitable to be injected into reservoirs to stimulate the conversion of CO2 into CH4.