Use of Polymers to Recover Viscous Oil from Unconventional Reservoirs – 2011

R.S. Seright – 2011

Abstract

Final report of the three-year viscous oil polymer flooding project. Fractional flow calculations definitively show that residual oil saturation (Sor) reduction during polymer flooding significantly improves recovery efficiency for viscous oils, across all viscosity ranges and waterflood histories. The impact of Sor reduction diminishes with increasing reservoir heterogeneity. A new sulfonic tetra-polymer associative polymer (Mw 12 to 17 million) provides higher viscosity in porous media than HPAM 3830S but loses 31 to 45 percent of low-flux resistance factor after exposure to 235 psi/ft shear stress, compared to only 0 to 15 percent for standard HPAM. After 2500 psi/ft shear, the associative polymer’s advantage over HPAM essentially disappears. Polymer gels complement polymer flooding for sweep improvement in heterogeneous North Slope reservoirs.

Key Takeaways

  • Residual oil saturation (Sor) reduction during polymer flooding significantly improves recovery efficiency even for highly viscous oils — and this benefit persists regardless of prior waterflood duration.
  • The impact of Sor reduction diminishes with increasing reservoir heterogeneity — in highly heterogeneous reservoirs, volumetric sweep improvement dominates over displacement efficiency gains.
  • A new sulfonic tetra-polymer associative polymer (Mw 12 to 17 million) provides higher viscosity in porous media than HPAM 3830S at equivalent concentration — but loses 31 to 45 percent of low-flux resistance factor after 235 psi/ft shear exposure.
  • After 2500 psi/ft shear stress, the associative polymer’s viscosity advantage over standard HPAM essentially disappears — near-wellbore shear must be carefully managed in field applications.
  • Polymer gels remain valuable complementary tools for sweep improvement in viscous-oil polymer flooding in heterogeneous North Slope reservoirs, especially where mobility control alone is insufficient.
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