Use of Polymers to Recover Viscous Oil from Unconventional Reservoirs – 2010

R.S. Seright – 2010

Abstract

Second year of the viscous oil polymer flooding project. Four questions are addressed. First, HPAM shear thinning in porous media can be observed at low salinity and high concentration but is slight or non-existent under practical EOR conditions — not a significant liability. Second, permeability reduction by polymers does not benefit vertical sweep efficiency, contrary to earlier claims; overall viscosity (resistance factor) is the key parameter. Third, polymer solution rheology (shear thinning vs. shear thickening vs. Newtonian) does not significantly affect sweep efficiency. Fourth, polymer flooding can be effective even after 5 pore volumes of prior waterflooding. Two biopolymers are evaluated: EX9719 xanthan provides 25 to 100 percent higher viscosity than standard xanthans with excellent filterability.

Key Takeaways

  • Under practical EOR conditions, HPAM shear thinning in porous media is slight or non-existent compared to shear thickening at high fluxes — not a significant liability for polymer flooding sweep efficiency.
  • Permeability reduction by polymers does NOT improve vertical sweep efficiency — contrary to earlier claims. Overall viscosity (resistance factor) is the key parameter for sweep improvement.
  • Polymer solution rheology (shear thinning, Newtonian, or shear thickening) does not significantly affect sweep efficiency in linear or radial flow, with or without crossflow.
  • Polymer flooding can remain effective even if waterflooding has been conducted for up to 5 pore volumes before polymer introduction — a commercially significant finding for late-start conversions.
  • CP Kelco EX9719 xanthan provides 25 to 100 percent higher viscosities than standard xanthans with excellent filterability — a strong biopolymer candidate for viscous-oil polymer flooding.
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