Injectivity Characteristics of EOR Polymers

R.S. Seright, Mac Seheult, Todd Talashek – 2009

Abstract

This paper estimates injectivity losses relative to water for EOR polymer solutions in the absence of open fractures, and considers the degree of fracture extension if fractures are open. Three principal EOR polymer properties affecting injectivity are examined: debris in the polymer, polymer rheology in porous media, and polymer mechanical degradation. An improved test was developed to measure polymer plugging tendency in porous media — demonstrating that plugging tendencies vary considerably among both HPAM and xanthan polymers. For xanthan solutions, pseudoplastic behavior in porous rock closely parallels viscometer behavior, and xanthan was remarkably resistant to mechanical degradation (only 19% viscosity loss at 24,600 psi/ft through 102-md Berea). HPAM in 573-md Berea showed Newtonian behavior at low-to-moderate fluxes and pseudodilatant (shear-thickening) behavior at high fluxes. The onset of mechanical degradation for HPAM occurred at 14 ft/d in 573-md Berea. Without fractures, satisfactory injection of more than 0.1 PV is expected only for the cleanest polymers.

Key Takeaways

  • Without open fractures, satisfactory injection of more than 0.1 pore volume of EOR polymer solution is only achievable for the cleanest polymers — plugging tendency is the critical injectivity constraint in unfractured rock.
  • An improved plugging test revealed large variability in plugging tendency among both HPAM and xanthan polymers — polymer selection for injectivity must be based on the specific polymer lot and supplier, not just the polymer type.
  • Xanthan rheology in porous media closely parallels viscometer behavior (pseudoplastic), and xanthan showed exceptional mechanical stability — only 19% viscosity loss at 24,600 psi/ft through 102-md Berea.
  • HPAM in 573-md Berea showed Newtonian behavior at low-moderate fluxes and shear thickening (pseudodilatant) at high fluxes — no pseudoplastic behavior was observed in porous rock, unlike in a viscometer.
  • The onset of mechanical degradation for HPAM occurred at 14 ft/d in 573-md Berea — above-parting-pressure injection with controlled fracture extension is required to avoid degradation at practical field injection rates.
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