Physical and Numerical Simulation of Shear-Rate Dependent Viscosity in Polymer Flooding

Abstract

AbstractHigh molecular polyacrylamides have been used widely in polymer flooding applications for improving oil production. The injected polymer is subjected to different shear rates and thus results in various performance. This paper integrates the behaviors of different laboratory experiments into a general workflow for evaluation of the impact of shear rate on oil production using numerical simulation. The impact of shear rates on the rheological property of a polymer solution was evaluated by injection of polymer solution into a core plug at different injection rates. The measured bulk viscosity and calculated apparent viscosity were fitted with different rheological models to identify flow behavior and the corresponding shear rate range. Shear rate at sand surface and shear rate profile from injector to deep formation were estimated using an inverted five-spot well pattern. Combination of the experimental results with the estimated shear rates was used to describe the flow behaviors of injected polymer solutions. The impact of shear-rate dependent viscosity on oil production was evaluated using a UTCHEM simulator. Laboratory experiments showed that polymer shear degradation occurs when the shear rate exceeds 4402 s−1 in a carbonate core plug with a permeability of 390 mD. The shear thickening was observed in the shear rate range of 90 to 4402 s−1. The injected polymer solutions flowing from injector to near producer experience four viscosity regimes in sequence, i.e., shear degradation, shear thickening, shear thinning and Newtonian. The scales of each regime are different. The critical shear rates upon mechanical degradation are closely related to perforation parameters including perforation size, density, and interval. When the polymer solutions is injected into a reservoir with permeability of 390 mD at a rate of 0.2 pore volume/year, shear degradation occurs within a radius of 0.2 m around the wellbore, and shear thickening behavior between a radius of about 0.2 to 10 m, and the regimes of shear thinning or Newtonian flow in the rest range over a radius of 10 m to deep formation. The numerical simulation results show that polymer viscosity loss leads to oil production reduction, and shear thickening has very little effect on oil production if no considerable injectivity declines. The paper provides a workflow for evaluating the impact of shear rates on oil production from laboratory experiments to well scale polymer flooding by numerical simulation studies.KeywordsPolymer floodingNumerical simulationShear rateRheological property