Low-Salinity Chase Waterfloods Improve Performance of Cr(III)-Acetate Hydrolyzed Polyacrylamide Gel in Fractured Cores

Bergit Brattekås, Arne Graue, Randall S. Seright – 2016

Abstract

This paper demonstrates that low-salinity water swells conventional Cr(III)-acetate-HPAM gels, significantly improving gel-blocking performance after gel rupture. Formed polymer gel was placed in fractured core plugs, and chase waterfloods were performed using four brine compositions, including three low-salinity brines. Injection pressure and matrix flow rate both increased with decreasing chase-water salinity. In some cores, the fracture was reblocked during low-salinity waterfloods — gel-blocking capacity was restored above the initial rupture level. Low-salinity water also improved matrix sweep during chase floods. Results were reproducible in both sandstone and carbonate outcrop cores.

Key Takeaways

  • Low-salinity chase water swells Cr(III)-acetate-HPAM gel placed in fractures, restoring and improving gel-blocking performance after initial rupture — a simple operational change with significant conformance improvement benefit.
  • Injection pressure and matrix flow rate during chase floods both increase with decreasing chase-water salinity — the lower the salinity relative to the gel solvent, the greater the gel swelling and blocking improvement.
  • In some cores, low-salinity waterfloods reblocked fractures that had already been opened — gel-blocking capacity was restored above the initial rupture level — providing a mechanism to revive partially failed gel treatments without re-injection of gel.
  • Low-salinity water also improved matrix sweep during chase floods beyond the gel-blocking effect — combining gel placement with low-salinity chase water provides benefits from both gel conformance control and low-salinity EOR.
  • Results were reproducible across multiple experiments and stable over long periods in both sandstone and carbonate outcrop core materials — demonstrating robustness across different lithologies.
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