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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMicrobially Improved Oil Recovery with both a surfactant producing and a non surfactant producing variant of Rhodococcus sp 094 has been tested through coreflooding laboratory tests. A goniometer was also used to measure interfacial tension and wettability for the fluid systems involved in the corefloodings. Significant reductions of interfacial tension have been measured for both variants of the bacteria. Wettabilities also changed and bacterial systems were more oil wet than their brine counterpart. The effect of bacteria concentration on overall recovery also became apparent.

Micromodel experiments have been executed in order to have better insight into the displacement mechanisms allowing Rhodococcus sp. 094 to increase oil recovery. Changes caused by the bacteria in the fluid interfaces and pore walls have been recorded and are presented. The previously suspected mechanisms are further confirmed by the results, but a much better insight into the details of how the process occurs has been obtained and a theory for this process is developed. Introduction Previous publications by the authors1, 2 have already stated the effectiveness of Rhodococcus sp. 094 to increase oil recoveries from Berea cores with pure hydrocarbons (dodecane) consistently with an additional 4 %1 and at the most favorable conditions with up to 9%2. The mechanisms suspected for the additional recovery have been: Selective plugging, interfacial tension (IFT) reduction3, and changes in wettability. In those publications, the work has focused on standard reservoir lab measurements, especially Berea corefloodings and interfacial tension and wettability measurements. Glass micro model experiments can complement very well these experiments, by providing a look into the process as it unfolds in the pore space. Even though the glass micromodels used have limitations from the larger pore size deriving from the fabrication process limitations, and from the homogenous and two dimensional geometry of the flow, they can still be an invaluable tool for understanding complex mechanisms, testing hypotheses and qualitatively provide a guide of the changes occurring in the pore space with different EOR methods. It was also possible to estimate the saturation by using image analysis software, which has made it possible to plot the enhanced oil recovery vs. the capillary desaturation curve (CDC). A total of ten experiments where brine and brine with either the surfactant producing or the non-surfactant producing variant of the Rhodococcus sp. 094 bacterium are presented. The results obtained in the micromodel flooding are analyzed in conjunction with the results from coreflooding experiments, and in this way a much better understanding of the mechanisms emerges, and a hypothesis can be proposed. By designing new experiments to test this hypothesis, it can be confirmed, improved or disproved.

Microbial Improved Oil Recovery (MIOR) processes use bacteria or their bioproducts to help mobilizing additional oil from the reservoir. The chemical and physical properties of the reservoir fluids and rock are changed during the MIOR process. An extensive investigation has been carried out at laboratory temperature with dodecane and an alkane oxidizing bacterium, Rhodococcus sp 094, suspended in brine to study potential recovery mechanisms involved in the MIOR process. Flooding experiments on Berea sandstone cores and flow visualization experiments within glass micromodels have shown the effects of bacteria on remaining oil saturation. The interfacial tension reduction, wettability alteration and selective plugging are recognized as important displacement mechanisms during the MIOR process. The objectives of this paper are to present the experimental results and to evaluate the driving mechanisms of MIOR by using two simulators. ECLIPSE is used to build a model based on core parameters for simulating the core flooding process. While, COMSOL Multiphysics models the two phases flow obtained experimentally at the pore scale within the micromodels. Simulation results are consistant with the experimental results and indicate that both tools are useful to solve the simulation problems of MIOR process. The obtained results address capability and inability of simulators to model the MIOR displacement mechanisms.

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