Effect of Residual Oil Saturation and Salinity on HPAM Rheology in Porous Media

R.S. Seright, Madhar Sahib Azad, Mohammad B. Abdullah, Mojdeh Delshad – 2023

Abstract

This paper experimentally clarifies how residual oil saturation (Sor), salinity, and temperature impact HPAM rheology in porous rock. HPAM rheology was determined in Berea sandstone for Darcy velocities from 0.01 to 100 ft/d, Sor from zero to 0.55, and krw from 0.03 to 1. Key findings: (1) residual oil moderates shear-thickening magnitude, but not enough to explain unexpectedly high HPAM injectivities in field polymer floods; (2) the [1-ϕ(1-Sor)]/[k·krw·ϕ(1-Sor)]^0.5 shift factor was validated with oil present; (3) the onset velocity for shear thickening was insensitive to salinity between 0.1% and 5% TDS; (4) the magnitude of shear-thickening resistance factors decreased with increased temperature by more than expected from water viscosity alone — a finding not explained by oxidative or mechanical degradation. Results are critical for predicting fracture initiation and HPAM viscoelasticity relevance in field polymer floods.

Key Takeaways

  • Residual oil moderates HPAM shear-thickening magnitude in porous media, but not sufficiently to explain the unexpectedly high injectivities relative to water observed in many field polymer floods using vertical injection wells.
  • The [1-ϕ(1-Sor)]/[k·krw·ϕ(1-Sor)]^0.5 shift factor was confirmed valid for predicting the shear-thickening onset velocity in the presence of residual oil — but contradictory literature reports suggest this remains unresolved in some conditions.
  • The onset velocity for shear thickening in HPAM solutions was insensitive to salinity between 0.1% and 5% TDS — a significant simplification for analytical and numerical polymer flood models.
  • Shear-thickening resistance factors decreased with increasing temperature by a factor greater than what water viscosity change alone predicts — this excess decrease cannot be explained by oxidative or mechanical polymer degradation.
  • This dataset provides key inputs for analytical and numerical models predicting fracture initiation pressure and the significance of HPAM viscoelasticity in field-scale polymer flood applications.
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