Capillary force limits the efficiency of water flooding by trapping the oil in porous media. High capillarity is caused by high interfacial tension (IFT) between oil and water that leads to a high residual oil saturation. Surfactants are widely used to reduce IFT and significantly mobilize the entrapped oil. However, the surfactants that are injected into a reservoir to lower the IFT several orders of magnitude may not be cost effective. A cost effective alternative for surfactant flooding is microbial enhanced oil recovery (MEOR). In the MEOR process, nutrients and natural bacteria are injected into a reservoir and both indigenous and injected microorganisms are able to react and then generate biosurfactants based on in-situ reactions.

Modeling a microbial enhanced oil recovery process requires coupling kinetics transport with local equilibrium transport in the presence of the surfactant phase behavior model (i.e. Hand's rule). In general, reservoir simulators do not model relative chemical reactions that consider the effect of essential environmental parameters such as temperature, salinity, and pH.

The main objective of this work is to present first order Monod kinetic equations as a function of temperature, salinity, and pH, which control the biodegradation reactions and microbial growth rate. This involves investigating the impact of biosurfactant adsorption, maximum growth rate, and nutrient concentration. Next, the effects of environmental factors are implemented in a four-phase chemical flooding reservoir simulator (UTCHEM). Finally, the simulator is used to history match coreflood experimental data to model the contribution of the cited parameters on oil recovery.

Results show that in-situ biosurfactant generation rates can be thoroughly modeled based on environmental factors and IFT can be reduced in a similar manner as surfactants. Simulation results show 10-15% incremental oil recovery using in-situ biosurfactant compared to waterflooding. The simulation results show that nutrient concentration, salinity and temperature are the most significant parameters influencing oil recovery, whereas pH has an insignificant effect.

The key findings of this work are the following:

  • In-situ biosurfactant generation in a MEOR process is mathematically described.

  • A new environmental model is implemented into the simulator.

  • Various parameters influencing the efficiency of the MEOR process are investigated.

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