Disproportionate Permeability Reduction With Pore-Filling Gels

R.S. Seright – 2009

Abstract

Pore-filling Cr(III)-acetate-HPAM gels are investigated as a more reliable approach to DPR. For porous media with pre-gel water permeability at Sor ranging from 120 to 6,500 md, a single pore-filling gel formulation consistently reduced water permeability to approximately 0.24 md (range 0.12–0.37 md) — essentially independent of initial permeability. In contrast, a commercially available relative-permeability modifier showed a much wider range of post-treatment water permeability (0.75–202 md) in Berea cores at 222–363 md. Several pore-filling gel formulations provided water residual resistance factors above 2,000 with ultimate oil residual resistance factors of 2 or less. Significant oil throughput is required to achieve low oil residual resistance factors, suggesting gelant penetration must be small (a few feet or less) for effective DPR.

Key Takeaways

  • Pore-filling Cr(III)-acetate-HPAM gels reduce water permeability at residual oil saturation to approximately 0.24 md regardless of initial rock permeability (tested from 120 to 6,500 md) — providing a reliable, permeability-insensitive DPR treatment outcome.
  • Commercially available relative permeability modifiers (RPM) show much greater variability in post-treatment water permeability (0.75–202 md in 222–363 md Berea) — a disadvantage compared to pore-filling gels for predictable water shutoff.
  • Water residual resistance factors above 2,000 combined with ultimate oil residual resistance factors of 2 or less are achievable with optimized pore-filling gel formulations — representing excellent selectivity for water over oil.
  • Significant oil throughput is required to dehydrate gel and restore oil permeability after gel placement — implying that gelant penetration into oil zones must be kept small (a few feet or less) to allow efficient cleanup within practical oil production timescales.
  • Pore-filling gels offer a pathway to treating both fractured and unfractured production wells for DPR without zone isolation, provided gelant volume is controlled to limit penetration into oil-producing zones.
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