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A fundamental study of microscopic mechanisms and pore-level phenomena in the Microbial Improved Oil Recovery method has been investigated. Understanding active mechanisms to increase oil recovery is the key to predict and plan MIOR projects successfully. This article presents the results of visualization experiments carried out in a transparent pore network model. In order to study the pore scale behavior of bacteria, dodecane and an alkane oxidizing bacterium, Rhodococcus sp. 094, suspended in brine, are examined for evaluating the performance of bacterial flooding in the glass micromodel. The observations show the effects of bacteria on remaining oil saturation, allowing us to get better insight on the mechanisms. Bacterial mass composed of bacteria and bioproducts growth in the fluid interfaces and pore walls have been recorded and are presented. No gas is observed throughout any of the experiments. The biomass blocks some pores and pore-throats, and thereby changing the flow pattern. As a consequent, the flow pattern change together with the previously proposed mechanisms, including the interfacial tension reduction and wettability changes are recognized as active mechanisms in the MIOR process.Keywords Reservoir engineering · MIOR · Glass micromodel · Bacteria and Oil-in-water emulsion Abbreviations MIOR Microbial improved oil recovery S orResidual oil saturation (%) S wir Irreducible water saturation (%) NSPB Producing bacteria SPB Surfactant producing bacteria

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Results of coreflooding experiments with Rhodococcus sp. 094 species have already revealed that the bacterium is able to increase oil recoveries up to 9 %. Subsequent investigations have been carried out in order to recognize the complex mechanisms. Although published results proposed wettability changes in core plugs and favourable changes in the flow pattern as the active mechanisms but the potential of interfacial tension (IFT) and contact angle parameters was not fully understood in an aerobic process. The present paper is a continuation of a series of laboratory experiments and consists of interfacial tension and contact angle measurements by an automated pendant drop goniometer. A refined hydrocarbon as the drop and two variants of bacteria suspended in brine as the continuous phase were employed. IFT and contact angle experiments were conducted in a static and a dynamic condition and quartz plates with two initial wettabilities were used. A certain volume of the bacterial solution and a short observation time is used in the static condition and the measurements show that by using bacteria, IFT is lowered from 18.3 mN/m (brine) to 13.6 mN/m (bacteria) and the contact angle changes slightly. However, our hypothesis is that the bacteria are capable of forming very stable emulsions of oil in brine and the real IFT value is much lower and the contact angle changes significantly. In the static condition, metabolic activities that lead to reduction of interfacial tension or contact angle changes are stopped due to the lack of nutrients and oxygen during the short observation period. Therefore a constant flow of fresh bacterial suspension with enough nutrients and oxygen is ensured in the dynamic status. The IFT and the contact angle values obtained are presented in both conditions. The results show that the interfacial tension in the case of continuous flow of fresh bacteria is close to 5 mN/m. It is also observed that the contact angle is lower in the dynamic system compared to the static system. The new experimental procedure is more suitable for investigation of IFT reduction mechanisms in aerobic microbial improved oil recovery processes.

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.