An Investigation of Retention and Unusually High Apparent Viscosity of Hydrophobically Associative Polymer in Porous Media

Abstract

Abstract In this study, we investigated the influence of polymer retention (both irreversible and reversible retentions) on the unusually high resistance factor provided by hydrophobically associative polymers (AP) in porous media. As a comparison, a commercial partially hydrolyzed polyacrylamide (HPAM) was also tested. Coreflood or dynamic method was used to assess retention (both irreversible and reversible) and resistance factor in sandstone cores at a flux of around 11 ft/d. To make fair comparison, in some corefloods, HPAM solutions was injected in the same core after the completion of associative polymer injection cycle. The results indicated: (1) the retention of fresh associative polymer was nearly four times of that from fresh HPAM and this was indicated by the residual resistance factor measurement. Resistance factor provided by fresh associative polymer was almost ten times higher than that from HPAM even though they showed similar viscosity property in a viscometer; (2) Compared with fresh HPAM, a substantial excess reversible retention (44.6 μg/g rock) was detected for fresh associative polymer that was comparable to its irreversible retention (41.0 μg/g rock); (3) Degraded associative polymer showed reduced irreversible retention (32.7% less) and almost no reversible retention difference was observed between associative polymer and HPAM. The resistance factor by degraded associative polymer was almost half of that from fresh solution. In the absence of excess irreversible and reversible retentions caused by HPAM, the degraded associative still provided much higher resistance factor than HPAM; (4) The unusually high resistance factor from associative polymer could be ascribed to the irreversible retention that caused permeability reduction, reversible retention which provided resistance to polymer flow in porous media without affecting core permeability, and also the intermolecular association between hydrophobic monomers in associative polymer.