The use of polymer floods to efficiently displace heavy oils with viscosities up to 10,000 mPa.s has be tested successfully in laboratory scale evaluations; commercial success on the field scale has been achieved with oil viscosities up to 2000 mPa.s in Western Canada1  and other parts of the world1 . Since it has been established that the polymer flood technology can be successful at displacing heavy oils on a field scale, it is timely to improve the efficiency of this technology. Researchers have shown that heterogeneities are more detrimental when waterflooding heavy oils than experience obtained from conventional waterfloods3, 4 . Hence, it is essential to understand the polymer flood displacement of heavy oil in the presence of heterogeneities. In addition, it was beneficial to conform the impact of large scale heterogeneities with judicious use of associative polymers.

Building a high and low permeability layer into a cylindrical sandpack allowed for demonstrating the impact of heterogeneities on a waterflood and polymer flood displacing heavy oils; the high permeability layer had a permeability 10 times greater than the low permeability layer. The reduced oil recovery in the heterogeneous, dual permeability core can be modeled correctly using a reservoir simulator if a capillary pressure difference curve is introduced during the simulations. The capillary pressure difference curve controls the degree of cross-flow from the high permeability layer to the low permeability layer and corrects the sweep efficiency.

Salinity and hardness tolerant associative polymers suitable for injection into reservoir core have been screened and developed for heavy oil displacement processes. These specialty polymers generate a higher in situ apparent viscosity by forming large hydrodynamic radii through association between polymer molecules. In reservoir applications, these associative polymers may generate tremendous resistance factors in high permeability streaks. The dual permeability corefloods demonstrated that associative polymers outperformed the regular partially hydrolyzed polyacrylamides in two aspects: (1) the associating polymer generated incremental oil recovery after HPAM recovery and (2) the mobility reduction (or resistance factor) of the associative polymers was significantly higher than HPAM. Hence associative polymers can be used for blocking and diverting purposes in high permeability layers where regular polymers may not be as effective.

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