Experimental Studies of Microbial Enhanced Oil Recovery
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The main purpose of this work was to understand the driving mechanisms by which the bacterium Rhodococcus sp. 094 increases oil recovery. The reason for only using this species was to thorougly investigate different aspects of it, to be able to answer as many questions as possible so that in the end it would be possible to confidently understand which mechanisms are responsible for enhanced oil recovery with this bacterium. From the lessons learned on this work one could more efficiently design a research project on other bacteria to investigate their driving mechanisms. A deep understanding of how any EOR method works is necessary in order to select the right method, and to correctly design its application, and in the case of MEOR there is a vast number of possibilities and variabilities. The experimental work made for this project has been comprehensive, with more than 100 core flooding experiments being carried out, 97 of which have been successful and have formed the main body of this research. Interfacial Tension measurements were made with a ring tensiometer and a goniometer, and contact angles have been measured by goniometry. Wettability was also measured by Amott test, and micromodel floodings were carried out. The potential of MEOR as a secondary drainage method has been tested against its use as a tertiary method, and two variants of the bacteria, a surfactant producing variant (SPB) and a non-surfactant producing variant (NSPB) were compared. How wettability of the rock affects the effectiveness of the MEOR process has also been studied, as well as the effect of the water salinity. Finally the particle like behavior of the bacteria was tested, to see whether the additional recovery effect is due to sweep efficiency improvement alone, caused by accumulation of particles. The experimental work carried out throughout the duration of this project has been presented as papers, and this are reproduced in the chronological order in which they were published. Comments have been added where the point of view of the author has varied at a later point as results from more experiments were obtained. From the initial hypothesis of the mechanisms being: interfacial tension reduction, wettability change and sweep efficiency improvement, it has now been established how the most important mechanism is sweep efficieny improvement, with interfacial tension reduction playing a smaller role, and wettability change not likely contributing significantly. Some insight has also been gained as to how MEOR is more complex than the traditional description of its main mechanisms, given that the bacteria, as living beings affect the recovery in a way in which particles or chemicals cannot.