Polymer Flood Incremental Oil Recovery and Efficiency in Layered Reservoirs Including Non-Newtonian and Viscoelastic Effects
Authors: Laoroongroj Ajana , Gumpenberger Thomas , Clemens Torsten 
Published: October 2014

Currently, OMV is performing a polymer solution injection pilot test into the 8 TH reservoir of the Matzen field in Austria. The reservoir is a heterogeneous sandstone, tracer tests revealed that the difference in flow velocity is more than a factor ten. The observed large heterogeneity and fast travel times raised the questions: what are the effects of the heterogeneity and non- Newtonian polymer rheology on the displacement efficiency?

Laboratory experiments were performed to investigate the rheology and retention of the high molecular weight polyacrylamide polymer solution. The experiments showed no significant retention. The rheology of the injected polymers indicated apparent shear-thickening with flow velocity. The effect of permeability on the apparent viscosity was larger than the apparent shear-thickening.

The results of the tracer tests and laboratory experiments were used in simulations of layered reservoirs with the properties of the 8 TH reservoir. Newtonian, shear-thinning and shear-thickening polymer solution rheology was applied for cases with and without crossflow.

Without crossflow, the highest incremental oil recovery factor is seen for shear-thickening behavior and the lowest for shear- thinning. The utility factor (uf = kg polymer injected/incremental barrels of oil production) is showing a minimum as a function of polymer injection slug size whereas the incremental recovery factor is increasing up to a polymer slug size of 1.2 PV injected.

With crossflow: in this case, the incremental oil recovery compared with the water flood is highest for shear-thinning followed by Newtonian and shear thickening behavior. The shear-thinning fluid travels faster in the high permeability channel, resulting in substantial cross flow of the polymer solution into the adjacent low permeability area. The cross-flow dominates over the effect of the polymers traveling at different speeds. The incremental oil recovery and utility factor are increasing with the slug size for all cases. Larger slug sizes of polymer injection result in higher utility factors and higher incremental oil recovery.

It should be noted that the influence of permeability on apparent viscosity of the polymer solution rheology is larger than the shear-thickening effects. Hence, although apparent shear-thickening might be observed in the laboratory for one lithology, the apparent viscosity in the reservoir might be higher in lower permeable layers despite the lower flow velocity than in high permeable layers.

Varying a number of parameters, the results indicate that the permeability contrast of high permeability and low permeability is not the most influential parameter for polymer solution projects in reservoirs with crossflow. Higher permeability contrast leads to poorer sweep efficiency of the water flood to which the polymer augmented flood is compared to. More oil is remaining in the reservoir for larger permeability contrast, polymer flooding tends to lead to increased incremental recovery factor with larger permeability contrast for the conditions simulated.