Quantification of the Viscoelastic Behavior of High Molecular Weight Polymers Used for Chemical Enhanced Oil Recovery

The main objective of this study was to validate a proposed Universal Viscosity Model (UVM) for the apparent viscosity of polymer solutions flowing in permeable media and to determine the parameters of this model and how they vary with the polymer characteristics. New rheological data for several polymers of current interest for both polymer flooding and other chemical EOR processes were measured and new coreflood data over a wide range of velocities were measured for this purpose. Two types of polymer were used: a partially hydrolyzed polyacrylamide (HPAM) and a co-polymer of acrylamido-methyl-propane sulfonate (AMPS) and acrylamide. Both steady shear and oscillatory measurements were carried out to determine the viscous and elastic components of the complex viscosity and to determine the relaxation time of the polymers. Core flood experiments over a wide range of flow rates were used to measure the apparent viscosity of these same polymer solutions. The viscosity of the polymer solutions was modeled using the Carreau model. The relaxation times of the polymer solutions were obtained by modeling the dynamic/oscillatory data using the Rouse model. The UVM parameters time constant, λ2, shear-thickening index, n2, and maximum viscosity before shear degradation, μmax, were determined by fitting the experimental data. All of the data could be fit with a constant value of the time constant, λ2 of 0.01. The shear-thickening was found to have a value of about 2.3. The most important conclusion of this study is that the UVM fits measured core flood data under a wide range of conditions for commonly used EOR polymers and can therefore be used to make predictions of apparent viscosity of these polymer solutions under certain conditions using only rheological data that are relatively inexpensive to measure compared to core flood data. This model can now be used in reservoir simulation studies of polymer flooding processes and other chemical enhanced oil recovery processes involving the use of polymers.Petroleum and Geosystems Engineerin