Fluid Diversion and Sweep Improvement With Chemical Gels in Oil Recovery Processes – 1991

R.S. Seright, F.D. Martin – 1991

Abstract

Second year of the gel fluid diversion study. Rock permeability and lithology effects on gel performance are characterized for Cr3+-xanthan, resorcinol-formaldehyde, and colloidal-silica gels. Disproportionate permeability reduction (DPR) is studied across different wettabilities: DPR is more pronounced in intermediate-wettability than strongly water-wet systems. All four gel types tested (resorcinol-formaldehyde, Cr-xanthan, Cr-polyacrylamide, colloidal silica) reduce water permeability more than CO2 permeability but experience breakdown during WAG cycles. Viscous gelants leak off from fractures into the matrix more than low-viscosity gelants. Design criteria for fracture applications: achieving a ratio of fracture penetration depth to matrix penetration depth greater than 10 times the matrix residual resistance factor is the target.

Key Takeaways

  • Residual resistance factors for Cr3+-xanthan and resorcinol-formaldehyde gels decrease with increased rock permeability; colloidal-silica gels show the opposite trend — an important screening distinction.
  • DPR is more pronounced in intermediate-wettability systems than strongly water-wet systems — reservoir wettability is a key candidate screening parameter.
  • All four gel types reduce water permeability more than CO2 permeability, but all experience some gel breakdown during WAG cycles.
  • Viscous gelants cause greater matrix leakoff than low-viscosity gelants during fracture injection — a counterintuitive finding with practical design implications.
  • For fracture applications, the design target is a ratio of fracture penetration depth to matrix penetration depth greater than 10 times the matrix residual resistance factor.
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