Wall-Effect/Gel-Droplet Model of Disproportionate Permeability Reduction

J. LIang; R.S. Seright – 2001

Abstract

This paper proposes a combined wall-effect and gel-droplet model to explain DPR. The wall-effect model applies when gelant matches the wetting phase — the gel forms a thin coating on pore walls, selectively blocking water flow while oil flows through the gel-free pore center. The gel-droplet model applies when gelant matches the nonwetting phase — gel forms discrete droplets that are more easily displaced by the nonwetting oil phase. The combined model predicts that DPR should increase with increasing residual nonwetting-phase saturation. New experimental results support this prediction, providing the first quantitative model that correctly captures the dependence of DPR magnitude on residual oil saturation.

Key Takeaways

  • The wall-effect model explains DPR for water-based gels in water-wet rock: gel coats pore walls (where water films reside), blocking water flow, while oil occupies the pore center and flows through the gel-free central pore space.
  • The gel-droplet model explains DPR for nonwetting-phase gels: discrete gel droplets in pore centers are more easily displaced and rearranged by oil pressure than by water, creating asymmetric permeability reduction.
  • The combined model makes a testable quantitative prediction: DPR magnitude should increase with increasing residual nonwetting-phase (oil) saturation — more oil present means more oil pathways remain open relative to water pathways.
  • New experimental results confirm the predicted dependence of DPR on residual oil saturation — higher Sor produces stronger DPR — providing the first successful quantitative model for DPR magnitude.
  • The model identifies residual oil saturation as a key screening parameter for DPR-based water shutoff candidate selection: formations with higher residual oil saturation at the treatment location should show stronger DPR from gel treatments.
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