Polymer flooding leads to enhanced oil recovery by accelerating oil production and improving sweep efficiency. However, owing to the higher viscosity, injectivity of polymer solutions is of some concern and is important to understand to predict incremental oil recoveries. Achieving high polymer injection rates is required to increase oil production rates.

In the field test performed in the Matzen field (Austria), polyacrylamide polymers have been injected for the past two years. Core flood experiments with these polymers showed a significant increase in apparent viscosity due to the viscoelastic properties of the polymer solutions. Also, severe degradation of the polymer solution at high flow velocities was detected. In addition to core flood experiments, flow experiments through fractures were performed. In these experiments, shear-thinning and limited degradation of the polymer solution was observed and quantified.

Detailed polymer injection simulations were conducted that included complex polymer rheology in the fractures and the matrix. The reservoir stress changes and its effects on the fractures were also taken into account due to cold polymer injection. The results of the simulations matched the field data both for water floods and polymer test floods.

The simulations revealed two distinct phases during injection of the polyacrylamide polymer solution

(1) injection under matrix conditions in an early phase resulting in severe degradation of the polymers and

(2) injection under fracturing conditions once the formation parting pressure is reached, leading to limited degradation of the polymers

The calibrated model was used to investigate the impact of polymer rheology and particle plugging on injectivity and fracture growth.

The results of the field test and the simulations indicate that screening of fields for polyacrylamide polymer projects need to include geomechanical properties of the reservoir sand and cap/base rock in addition to the conventional parameters used in the simulations such as oil viscosity, water salinity, reservoir temperature and reservoir permeability. Furthermore, it is shown that water quality is crucial for polymer EOR operations