The recovery of viscous oil can be significantly improved by injecting polymer solutions. The processes leading to increased oil production occur on a large scale—improving vertical and areal sweep efficiency—but they begin on a microscale.
Micromodels with realistic pore geometries have been created. These micromodels were saturated with viscous oil, and the displacement of the oil by water and polymer solutions was investigated experimentally. Polymer injection reduced fingering compared with water injection and increased sweep efficiency accordingly.
The micromodel pore-network geometry was digitized with scanning electron microscopy (SEM). The digitized model was used to perform computational-fluid-dynamics (CFD) simulation of the displacement processes.
The displacement efficiencies and displacement patterns of the CFD simulations with water, polymer solutions, and polymer solutions after water breakthrough at the outlet end to displace oil were very similar to the results of the micromodel experiments.
Then, the CFD simulations were used to investigate the displacement at the pore scale. Water injection leads to the creation of fingers along slightly more-permeable flow paths. The number and length of the fingers decrease if polymer solution is injected. Even for polymer injection after water breakthrough, the fingering is reduced, polymer solutions are diverted into less-favorable flow paths, and sweep efficiency is increased.
CFD simulations can also be used to look into non-Newtonian fluid behavior at the pore scale. The polymers injected in the micromodel experiments exhibited shear-thinning behavior. On a pore scale, CFD simulations showed that the shear stress and viscosity of the polymer solutions accordingly are significantly lower in the pore throats than in the pores. Thus, the displacement efficiency of the polymer solutions is affected by the shear-thinning behavior.
The CFD simulations are in remarkable agreement with the micromodel experiments and can be used to quantify the displacement processes at pore scale.