Placement Properties of Foams Versus Gelants When Used as Blocking Agents

H.B Nimir, R.S. Seright – 1996

Abstract

This paper investigates whether foams can show placement properties superior to those of gels and gelants when used as blocking agents for conformance control. Specifically, whether the concept of limiting capillary pressure can be exploited to form a persistent, low-mobility foam in high-permeability zones while preventing foam from entering and damaging low-permeability zones. Using a C14-16 alpha-olefin sulfonate and nitrogen, foam mobilities were measured in cores with permeabilities from 7.5 to 900 md at 750 psig back pressure and 104°F, with foam qualities from 50% to 95% and Darcy velocities from 0.5 to 100 ft/d. Residual resistance factors during brine injection after foam placement were also extensively characterized.

Key Takeaways

  • Foams are investigated as potential alternatives to gels and gelants for selective conformance control — specifically examining whether limiting capillary pressure can enable foam to selectively block high-permeability zones without entering low-permeability oil zones.
  • Foam mobilities were measured across a wide range of conditions: permeabilities from 7.5 to 900 md, foam qualities from 50% to 95%, and Darcy velocities from 0.5 to 100 ft/d — providing comprehensive foam characterization data for conformance design.
  • The limiting capillary pressure concept theorizes that foam stability depends on pore capillary pressure — in high-permeability rock (lower capillary pressure), foam is stable and provides low mobility; in low-permeability rock (higher capillary pressure), foam collapses, providing high mobility and no blocking.
  • Residual resistance factors during brine injection after foam placement provide the key metric for assessing long-term conformance improvement — characterization of this parameter across the permeability range is essential for treatment design.
  • The experimental framework developed in this paper — measuring foam mobility and RRF across wide permeability, quality, and velocity ranges — provides the data foundation for comparing foam placement selectivity against that of gels and gelants.
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