Polymer-producing microorganism Clostridium sp. strain TU-15A was isolated from reservoir brine of Jilin Oilfield, China. TU-15A produces polymer in a molasses medium and increases the viscosity of the culture solution to 70cP by 10days cultivation. It's expected to be an effective microorganism for MEOR. In this study, a simulator was developed in order to analyze the mechanisms of MEOR using polymer-producing microorganism. The numerical model in this simulator consists of 2-phases(oil and water) and 5-components(oil, water, microorganism, nutrient and polymer). This model includes almost all processes of MEOR such as growth and death of microorganism, nutrient consumption, polymer production, water viscosity increment, improvement of the flow profile in a reservoir and enhancement of oil recovery. The validity of this simulator was shown by a comparison of both results of the numerical simulation and a flooding experiment. The quantitative change of microorganism, nutrient, polymer(water viscosity) and oil saturation were analyzed by a simulation of MEOR using polymer-producing microorganism on quarter of fivespot pattern flooding. Regarding the alteration of flow pattern in the reservoir, it was found that (1) the polymer produced by microorganism in reservoir flew into the main flow channel along the shortest way between the injection and production wells and water viscosity there increased, (2) subsequently more uniform flow profile of injected water as a postflash was established, and (3) the residual oil was mobilized to the production well. The additional oil recovery of 10% or higher was obtained at the early stage of the postflash. Our simulator will be a first comprehensive simulator for MEOR using an existing strain that produces polymer strongly. By using this simulator, the phenomena occurred in a reservoir on MEOR using a polymer-producing microorganism have been clarified and the high performance of this MEOR process have been demonstrated. Introduction In Microbial Enhanced Oil Recovery(MEOR) processes, microorganism(s) and nutrient(s) are injected into reservoir, and the microorganism(s) increases and produces metabolites such as polymers, surfactants, gases and/or acids in reservoir. These metabolites help to mobilize the residual oil. In the past, high potential to enhance oil recovery of MEOR process have been shown by many laboratory experiments and field trials. However, it is important to analyze not only the enhancement of oil recovery by microorganisms but also the mechanisms in MEOR process. There have been a few studies analyzing the mechanisms in MEOR process using mathematical simulators. A simplified numerical model were proposed by Baracat et al.1 and Knapp et al.2. Both their numerical models consisted of 1-phase(water) and 2-components(water and microorganism). In their numerical models, growth of microorganisms, absorption of microorganisms to the rock surface and diffusion of the microbial cells in porous media were modeled using fundamental conservation laws such as Monod equation and Langmuir equation. Their mathematical simulators were able to predict the reductions of porosity and permeability that were caused by the growth of microorganisms and the absorption of microorganisms to the rock surface.

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Abstract:In this paper, firstly, the establishment of quantitative evaluation techniques of capabilities of anaerobes in improving oil recovery is discussed, and then results of flooding experiments based on the techniques are presented.Strain 9A, which was recognized as one of useful anaerobes through the studies reported in previous papers, was incubated in porous media to investigate effects of kerosine on its growth. As a result, the cultivation showed that kerosine itself had no influence upon the microbial multiplication and metabolism.The flooding apparatus includes the sandpack which was comprised of an acrylic pipe packed with silica sands, injection pump and pressure measurement tools. The evaluation method was specified in this paper as follows; (1) making a sandpack, (2) measurement of water permeability, (3) saturating oil into the sandpack, (4) water flooding, (5) injecting microbes into the sandpack, (6) cultivation, and (7) recovering additional oil by injecting water. Regarding the microbial injection specified above at 5th clause, the minimum amount of liquid medium with microbes for uniform injection was decided through the investigation. Filteration of microbes did not occur.Then flooding experiments based on the above method were carried out using 9 kinds of anaerobes. Consequently, the oil recovery was improved at all cases. Especially, the maximum oil recovery obtained with strain 9A amounted to 30% of residual oil.

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Abstract:This paper describes the evaluation of activities of isolated anaerobes mentioned in the previous report. These anaerobes were incubated in culture bottles packed with silica sands, and after cultivation amount of gases produced, pH and interfacial tension of media were measured, as well as total growth. Results show that there are effective anaerobes which have gas and acid productivities in porous media. The lowest pH of 3.4 was obtained with Strain 8L. The matabolic gas analysis shows that the main components are carbon dioxide and hydrogen. Especially, Strain 4D, 7A-1 and 9A produced a large amount of carbon dioxide.From the economic point of view, the 4% molasess medium without any additives was also used for cultivation, and it was found that Strain 7A-1 and 9A out of 6 strains maintained their abilities as high as in the case of cultivation in the medium of molasses with Nutrient Broth.In addition, the growth rate and penetration ability of Strain 9A in porous media were evaluated.Results showed the micro culture space had a small effect on its growth rate, but no effect on the total growth, and Strain 9A was able to move freely through the sandpack.All the results so far mentioned imply that at least Strain 9A may be applicable to MEOR.