Radial Injectivity of an Associative Polymer for EOR

Hydrophobically modified polyacylamides (HMPAMs), also known as associative polymers, have high potential as EOR chemicals due to their specific chemical properties. However, the strength of hydrophobic interactions also leads to more complex flow behavior. Mostly, polymer injectivity is studied in linear coreflood experiments. However, in reality the polymer injection occurs in radial flow. The main difference is that linear flow has constant pressure gradient and thereby constant shear rate, while radial flow has a position dependent pressure gradient and therefore a shear gradient in the near-well region. For complex non-Newtonian polymers like HMPAMs this may have large implications for injectivity. The influence of relatively weak hydrophobic interactions on flow properties was studied by radial injection of a semi-dilute solution of associative polymer under high injection rates. Radial flow was achieved by injection in a well placed in the center of a 30 cm diameter, 3 cm thick disc cut from Bentheimer outcrop sandstone. Bentheimer was chosen due to the high homogeneity of the rock. Pressure ports were positioned between the injection well and the rim to allow determination of the pressure decay curve during flow. Effluent was collected and analyzed for mechanical degradation. The radial injection of the associative polymer showed shear thinning behavior at all rates, including at near-well equivalent rates. This means that this polymer can be injected with relatively low pressures and will gain viscosity as it propagates further from the well. Interestingly, this is different from the observations in linear core floods. Disruption and regeneration of weak hydrophobic interactions appears to be the main cause of the change in rheological behavior between linear and radial flow. The associative polymer showed excellent shear stability with only moderate viscosity reduction at extreme injection rates. The results confirm the need for in-situ measurements of polymer rheology not only in linear but also radial flow as input data for injectivity modeling. The experiments reveal that the associative polymer has different rheological behavior in bulk, linear and radial flow. The near-Newtonian behavior at near-well injection rates combined with building of viscosity at lower rates further from the well is beneficial for application in polymer flooding. This is to our knowledge the first systematic investigation of an associative polymer in radial flow. The results have major implications for polymer flood modeling and flood design, particularly for injections in vertical wells where injectivity is critical.