Simulation of microbial enhanced oil recovery processes

From an order of magnitude analysis of the importance of the possible mechanisms of microbial enhanced oil recovery (MEOR) processes, it is shown that biosurfactants have the highest potential to recover residual oil from a waterflooded reservoir. Cell mass and biopolymers may help to recover residual oil by improving the mobility ratio or by selectively plugging the high permeability layers in a layered reservoir. A compositional numerical simulator is developed for simulating the transport and growth of bacteria and oil recovery in MEOR processes. The simulator can be used for predicting the transport and growth of bacteria in porous media, reduction of permeability from the retention of bacteria, consumption of nutrient, production of biosurfactants and biopolymers, oil production rate and cumulative oil recovery as a function of pore volumes of fluid injected.; It is found that the permeability, the permeability contrast between layers, ratio of bacteria size to mean pore size, injected concentration, retention and growth parameters, and effective radius parameters are important in the transport and growth of bacteria in porous media. During bacterial suspension injection in a two-layer system, the low permeability layer is damaged more than the high permeability layer. These results show that for the selective plugging process to be effective, it is necessary to ensure zonal isolation to prevent bacteria injection into the low permeability layer.; From laboratory experiments of bacteria transport and growth in porous media the important parameters that control these processes are identified. Experiments were conducted with the facultative species, Bacillus Licheniformis (JF-2), in sandpacks for single- and two-phase flow. The effects of flow velocity, injected concentration, degree of dispersion, salinity, temperature, and the presence of a residual phase were investigated. The retention of bacteria and permeability reduction is significantly higher in the first few centimeters ({dollar}sim{dollar}2.5 cm) of the porous medium as compared to the downstream sections. The log-jam effect seems to be the primary mechanism for bacteria retention and permeability reduction in the upstream section, but for downstream sections size exclusion may be the dominant mechanism. Added dispersants (polyvalent anions), low salinities, and higher temperatures enhanced bacteria transport. This clearly shows the importance of coagulation and bridging in the retention of bacteria. In contrast to the results from flow in a single-phase system the presence of a residual oil phase increases bacteria retention.; Finally laboratory experiments were simulated numerically and the results were compared with the experimental data. Reasonably good agreement was obtained in all the cases studied. Empirical fractional flow functions for bacteria flow were used to approximately simulate the various retention mechanisms. This approach is shown to be useful in simulating the flow of complex colloidal suspensions in porous media.