In the North Sea average recoveries are reported to be above 40% of initial oil in place. The Norwegian Petroleum Directorate in 2001 set a target of 50% recovery for the Norwegian sector of the North Sea and it was envisioned that EOR techniques could be used to achieve this target. However, many oil companies rely primarily on infill well drilling to increase recovery factors as their default option because with the information that they have they can target new wells to recover bypassed oil. EOR techniques involve a greater degree of uncertainty in predicating recovery factors, and therefore, risk and economic assessments are more difficult to perform Awan et al. (2008).

Addition of polymer to injection water increases the viscosity of the water and hence reduces the mobility of the displacing fluid, increasing the microscopic sweep efficiency. Macroscopic sweep efficiency is also improved by the reduction in channelling in heterogeneous reservoirs. Initially the polymer slug is displaced primarily into the high permeability zones so the mobility in these high permeability zones is reduced disproportionally. Subsequently injected fluid will increasingly displace hydrocarbons from the low permeability zones, improving overall sweep efficiency.

Infill well drilling does not impact microscopic sweep efficiency but seeks to improve the macroscopic sweep efficiency by targeting oil that has not been swept by water. Due to gravity effects this bypassed oil is often to be found near the top of the reservoir and referred to as attic oil.