Modeling of in-situ Microbial Selective Plugging for EOR under Reservoir Environment in Multi-layered System

Abstract

Due to the eco-friendly and economical effectiveness, the microbial enhanced oil recovery (MEOR) process has been focused as a promising alternative to conventional enhanced oil recovery (EOR) methods. Despite its various advantages, the technique is not widely applied because of the uncertainties by uncontrollable bacterial activities in practical field applications. In addition, the reservoir conditions such as temperature, pressure, and salinity are extremely harsh for microbial survival. In this study, an accurate microbiological model incorporating the environmental effects has been developed and the efficiency of MEOR process based on selective plugging by microbial biopolymer generation has been examined in multi-layered system with high permeability contrast.

The stoichiometric equations are used to describe the growth and metabolic activities of dextran-producing Leuconostoc mesenteroides, and the reaction rates are calculated using the Arrhenius equation. The model is validated by matching the simulation results with data from batch and sandpack experiments. The advanced reaction rate equations are derived by modifying stoichiometric and Arrhenius equations to incorporate the effects of reservoir conditions. Therefore, microbial metabolisms are mathematically formulated to describe the combined effects of temperature, pressure, and salinity.

After comparing the results of microbial growth and dextran production due to environmental effects, MEOR is applied to multi-layered reservoirs of different environmental conditions. In optimum growth temperature reservoir, the permeability reduction due to selective plugging is the largest and the improvement of oil recovery is also the highest (49%) compared to waterflooding. When the MEOR is applied to a high temperature reservoir which is not suitable for microbial growth, there is an optimum injection temperature that can greatly improve the oil production. The oil productivity in the high pressure reservoir is estimated to decrease by 15% when the pressure effect is incorporated. Through the simulations of different salinity conditions, it is found that oil recovery is decreased with increasing salinity and only affected by injected water salinity.

The oil recovery obtained by the developed model including all three environmental effects is estimated to be 21% lower than that of the previous model. With previous model without the environmental effects, MEOR efficiency is considerably overestimated. In actual field conditions, MEOR efficiency can be improved up to 7% through optimized injection design. The results show the possibility of accurate evaluation of MEOR and promising potential of the technology.