Impact of Permeability and Lithology on Gel Performance

R.S. Seright – 1992

Abstract

This paper investigates the effects of rock permeability and lithology on the performance of four gel systems: resorcinol/formaldehyde, colloidal silica, Cr(III)-chloride-xanthan, and Cr(III)-acetate-polyacrylamide. Attention is paid to pH effects on gelation, gel performance as a function of fluid velocity, and tracer measurements of pore-space gel occupancy. The study demonstrates that gel performance cannot be adequately characterized using single-permeability rock — effectiveness must be assessed across the permeability range of the target formation to determine whether a treatment will enhance or harm oil production.

Key Takeaways

  • Gel performance must be characterized across multiple permeabilities and lithologies — single-permeability experiments reveal nothing about whether a diversion treatment will enhance sweep or damage oil-productive zones in stratified reservoirs.
  • The key criterion: the ratio of permeability reduction in the thief zone vs. the oil-productive zone must exceed the permeability contrast between those zones — only then does the treatment improve sweep efficiency.
  • pH effects on gelation are critical for all four gel types studied — resorcinol/formaldehyde, colloidal silica, Cr(III)-xanthan, and Cr(III)-acetate-polyacrylamide all show pH-dependent gelation behavior that must be controlled during field injection.
  • Tracer studies measuring gel-occupied pore fraction provide essential information about whether gel has filled the target pore space or merely plugged near the core face — distinguishing effective diversion from near-wellbore damage.
  • Velocity-sensitive residual resistance factors mean near-wellbore and deep-reservoir gel performance differ substantially, requiring velocity-profile-aware design for injection well applications.
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