Modelling of polymer retention during low concentrated HPAM polymer flooding in the heterogeneous reservoirs

Abstract

The polymer retention has been regarded as one of the major concerns in the operating process. The polymer retention includes adsorption, mechanical entrapment, and hydrodynamic retention. Retention by mechanical entrapment occurs when large polymer molecules become lodged in narrow flow channels. A number of studies found that considerable amounts of emulsions are retained at junctions between two different permeability zones, with maximum retention at the front portion of the low permeability zone. Large permeability reductions are also found. These papers imply the strong dependence of retention on the permeability. In addition, researches associated with polymer flooding have identified the characteristic of polymer retention. Overall, polymer retention is attributed to both adsorption onto surfaces and entrapment within small pores. Adsorbed polymers induce greater resistance to flow in low-permeability layers than in high-permeability layers, although the radius of penetration is greater for high-permeability layers. Traditionally, retention has been modelled as only adsorption using Langmuir's adsorption model, even though macromolecules are retained in different locations within pore spaces. Therefore, the model of polymer retention needs to be modified with respect to pore size, which is strongly related to permeability.