Abstract

Partially hydrolyzed polyacrylamide (HPAM) and related polymers are widely used as mobility control agents in all chemical EOR applications, and an accurate characterization of their apparent viscosity in the reservoir rock is crucial for design and performance evaluation of these processes. Their apparent viscosity in porous media generally decreases as flow velocity increases; however, beyond a certain critical velocity, the apparent viscosity sharply increases, showing shear-thickening behavior. A procedure to predict both the shear-thinning and shear-thickening apparent viscosities, from the rheometer-measured shear and oscillatory viscosities, has been developed earlier and validated with corefloods (Delshad et al., 2008). In addition to the shear viscosity database developed earlier (Lee et al., 2009), a database of the oscillatory viscosities of the EOR polymers was therefore developed for wide ranges of polymer concentration, NaCl salinity and calcium content, and temperature. The generalized Maxwell model (GMM) is employed to estimate the relaxation time of the polymer solution, by making non-linear fitting of the measured G' and G" data to GMM. Empirical correlations were developed to predict the relaxation time, which is subsequently used to quantify the shear-thickening portion of the apparent polymer viscosity under different process conditions. The apparent viscosity estimated matches reasonably with the available coreflood data.

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