Rheology of Gels Used for Conformance Control in Fractures

Jin Liu, and R.S. Seright – 2001

Abstract

This paper investigates whether gel behavior in rheometers correlates with behavior during extrusion through fractures. Qualitative similarities were noted between rheometer results and fracture extrusion data, but the pressure gradients during gel extrusion through fractures were substantially greater than values expected from rheological measurements. Also, the pressure gradient for gel extrusion through fractures varied with fracture width in an unexpected manner. These discrepancies point to a mechanism beyond simple bulk rheology — later work by Wang and Seright identified the wormhole flow mechanism as the explanation.

Key Takeaways

  • Gel rheology measured in a rheometer shows qualitative similarities to behavior during fracture extrusion — qualitative trends in viscosity and pressure gradient direction are consistent between the two measurement methods.
  • Quantitative pressure gradients during gel extrusion through fractures are substantially greater than values predicted from rheological measurements — simple bulk rheology cannot be used to directly design gel fracture treatments.
  • The pressure gradient for gel extrusion through fractures varies with fracture width in a manner that is unexpected from bulk rheology — the scaling is different from what simple shear-flow models would predict.
  • These discrepancies motivated further investigation that ultimately led to the wormhole-flow model — where mobile gel flows through narrow wormholes in concentrated immobile gel — which explains why fracture gradients far exceed bulk-rheology predictions.
  • Rheometer measurements remain useful as relative comparisons between gel formulations and for monitoring gelation progress, but cannot substitute for fracture extrusion measurements in absolute treatment design.
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