Currently there is no commercial reservoir simulator used to model the growth phase of microbial enhanced oil recovery (MEOR), due to process complexity and significant dependency on laboratory data. One of the work packages of the project "MEOR Studies" being conducted by Wintershall is dealing with the modeling of MEOR to allow the reservoir simulation of the planned pilot. The reaction kinetics option of STARS/CMG is applied as analogy to Monod equation, which is usually used to model bacteria lifetime. One reaction is applied for bacteria growth and metabolite generation, mainly using the stoichiometric coefficients, whereas a second reaction is used to simulate decay of used substances. The parameters are calibrated by matching batch experiments measuring optical density (OD) of an enriched culture consisting of various strains isolated from one of the screened Wintershall fields.
All components of MEOR are modeled as tracer in water and/or oil phases. The EOR effects are modeled as function of the produced metabolites. Using this concept following primary MEOR effects are successfully modeled: reduction of oil viscosity by generated CO2, IFT reduction by bio-surfactant and increase in water viscosity by bio-polymer. Furthermore, the adsorption option of STARS is used for modeling the selective plugging effect created by biomass.
The validation of the new MEOR modeling approach is performed by using the results of sandpacks and coreflood experiments. In homogeneous sandpacks the additional 5–9 % oil of OOIP due to IFT reduction and rheology change in displacing phase was successfully modeled.