Impact of Dispersion on Gel Placement for Profile Control

R.S. Seright – 1991

Abstract

This study explores the influence of diffusion, dispersion, and viscous fingering during placement of gels for injection profile modification. These phenomena usually will not eliminate the need for zone isolation during gel placement in unfractured injection wells. During gel placement in parallel laboratory corefloods, diffusion and dispersion can cause one to conclude erroneously that zone isolation is not needed in field applications. Gel treatments are more likely to improve sweep efficiency in wells where fractures are the source of the channeling problem. The study evaluates the effect of each phenomenon across a range of permeability contrasts and well types.

Key Takeaways

  • Diffusion, dispersion, and viscous fingering during gel placement in unfractured injection wells generally will not eliminate the need for zone isolation — these phenomena provide insufficient selective protection for oil-productive zones.
  • Parallel laboratory corefloods can give misleading results: diffusion and dispersion effects in corefloods may create the false impression that zone isolation is unnecessary, leading to incorrect design conclusions for field applications.
  • The discrepancy between coreflood and field scale results occurs because diffusion and dispersion are relatively more important at the small length scales of laboratory cores — at field scale, viscous forces dominate and provide less natural protection.
  • Gel treatments are more likely to improve sweep efficiency in wells where fractures are the primary source of channeling — the linear flow geometry and extreme permeability contrast of fractures provide inherent selectivity that diffusion and dispersion cannot replicate in unfractured wells.
  • Viscous fingering during gel placement can affect gelant invasion patterns, particularly in high-permeability-contrast systems, but does not provide consistent selective protection for oil-productive zones across the range of conditions studied.
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