Injectivity Behavior of Copolymer and Associative Polymers Decoded Using Extensional Viscosity Characterization: Effect of Hydrophobic Association

摘要

Associative polymer (AP) solutions in general exhibit higher resistance factors and subsequently lower injectivity than hydrolyzed polyacrylamide (HPAM) because of strong extensional flow characteristic in porous media despite having similar shear viscosity. From a scientific point of view, the challenge is to understand and quantify these properties in terms of the nature of their association in water. The kind of hydrophobic association (intramolecular or intermolecular) that AP exhibit is concentration dependent and will influence not only the shear but also the extensional properties and therefore elongational flow as well in the porous media. Therefore, the role of hydrophobic association on shear and extensional rheology and its effect on the injectivity in porous media requires comparative investigation over its counterpart nonassociating HPAM. Unlike shear rheology, measurement of bulk extensional properties for relatively low viscous enhanced oil recovery polymer solutions remains a challenge. In this study, extensional rheology measurements are performed using capillary breakup extensional rheometer (CaBER). The CaBER setup uses a stepstrain to stretch a droplet of liquid placed between the two plates and follows its midplane diameter that declines exponentially in the intermediate time scale where the filament breakup is governed by the balance between driving surface tension and resisting elastic force. The midpoint diameter is fitted with the upper-convected Maxwell model to determine the extensional relaxation time. Extensional viscosity calculated using the axial force balance at the critical Deborah number (Decr) determined using finitely extensible nonlinear elastic model would be indicative of polymer's elasticity along with polymer's relaxation time. These extensional parameters are further used for correlating with resistance factors and injectivity experimental data.