Prediction of Xanthan Rheology in Porous Media

W.J. Cannella, C. Huh, R.S. Seright – 1988

Abstract

The flow behavior of xanthan in porous media was investigated experimentally and theoretically using effective medium theory. Rheological behavior was tested over a wide range of concentrations (300–1600 ppm), permeabilities (40–800 md), residual oil saturations (0–29%), temperatures (25–80°C), and lithologies (sandstone and carbonate). An apparent shear rate equation with no adjustable parameters was effective for correlating porous media flow with viscometer data. Unlike capillary bundle models, the experimental constant was larger, attributed to channel connectivity and variable cross-sections. Theoretical modeling using percolation theory for power-law fluids supported experimental findings, showing that xanthan predominantly flows through larger pores due to its shear-thinning nature.

Key Takeaways

  • A single apparent shear rate equation with no adjustable parameters successfully correlates xanthan rheology in porous media across the full experimental range of concentrations, permeabilities, oil saturations, temperatures, and lithologies tested.
  • The shear rate dependence on Darcy velocity (first order) and on permeability (negative one-half order) agrees with capillary bundle model predictions — but the constant coefficient is larger than the model predicts, requiring effective medium theory to explain.
  • Effective medium theory based on percolation theory explains why the capillary bundle model underpredicts the shear rate constant: channel connectivity and variable cross-sections in real porous media cause a shear-thinning fluid to preferentially flow through the widest channels, bypassing small pores and increasing the apparent shear rate relative to a simple capillary bundle.
  • Xanthan rheology in porous media is robust across a wide range of conditions — residual oil saturation (0–29%), temperature (25°C and 80°C), and rock lithology (sandstones and carbonates) do not fundamentally alter the apparent shear rate correlation, simplifying its use in simulation.
  • This foundational xanthan rheology framework — linking viscometer data to porous-media behavior through a single correlation — remains the basis for xanthan simulation in polymer flood and profile modification applications.
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