Use of Preformed Gels for Conformance Control in Fractured Systems

R.S. Seright – 1996

Abstract

This paper studies preformed Cr(III)-acetate-HPAM gels using wide ranges of gel age, gel velocity, and fracture conductivity. Gels exhibited shear-thinning behavior in fractures and tubes correlated with gel superficial velocity and fracture width or tube diameter. In narrow fractures, gels dehydrated during extrusion, reducing the rate of gel propagation — an effect more pronounced as fracture width decreased. A numerical study compared placement of preformed gels and water-like gelants, examining ideal placement locations in fractures.

Key Takeaways

  • Preformed Cr(III)-acetate-HPAM gels exhibit shear-thinning behavior in fractures and tubes, with flow behavior correlated to gel superficial velocity and fracture width — this behavior enables predictive modeling of gel placement.
  • In narrow fractures, gels dehydrate during extrusion, slowing gel propagation rate — the effect is more pronounced as fracture width decreases, meaning treatment volume must be increased to achieve target penetration in narrow fractures.
  • Preformed gels provide an advantage over water-like gelants for near-wellbore fracture treatment: they do not flow through porous rock after gelation, so all injected volume concentrates in the fracture network rather than invading the matrix.
  • Gel age affects flow behavior — older, more structured gels exhibit higher pressure gradients during extrusion for a given velocity and fracture width, which must be accounted for in injection schedule design.
  • The comparison of preformed gels vs. gelants using a numerical model provides a design framework for selecting between the two approaches based on fracture width, treatment depth, and desired blockage profile.
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