Effect of Cr³⁺ on the Rheology of Xanthan Formulations in Porous Media

R.S Seright, F.D. Martin – 1992

Abstract

This paper tests key assumptions used in calculations of non-Newtonian gel placement in injection wells for Cr(III)-xanthan gels in Berea sandstone. Three assumptions are tested: whether pre-gelation porous-media rheology is unaffected by Cr(III) addition; whether post-gelation residual resistance factors are independent of fluid velocity; and whether gel is immobile under flow. Results: Cr(III) at 90 ppm does not significantly alter xanthan rheology before gelation. After gelation, residual resistance factors are NOT velocity-independent — they increase at higher velocities. The validity of this assumption in prior gel placement calculations is thus challenged

Key Takeaways

  • Cr(III) addition at 90 ppm does not significantly alter xanthan rheology in porous media before gelation — the pre-gelation flow behavior can be characterized from xanthan-only measurements, simplifying placement calculation inputs.
  • After gelation, residual resistance factors for Cr(III)-xanthan gels are NOT independent of fluid velocity — they increase at higher velocities, violating a common assumption in gel placement calculations.
  • Velocity-dependent post-gelation RRF means near-wellbore (high-velocity) and deep-reservoir (low-velocity) gel performance differ — constant-RRF placement calculations will misrepresent the actual treatment profile.
  • Gel mobility under flow conditions is a critical assumption for placement calculations — if gel is mobile, placement predictions based on immobile gel assumptions will be incorrect.
  • These experiments define which assumptions in non-Newtonian gel placement calculations are valid and which require revision — providing a more reliable mechanistic foundation for injection well gel treatment design.
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