Washout of Cr(III)-Acetate-HPAM Gels From Fractures: Effect of Gel State During Placement

B. Brattekås, S. G. Pedersen, H. T. Nistov, Å. Haugen, and A. Graue, J.-T. LIang, R.S. Seright -2014

Abstract

This work investigates blockage performance of Cr(III)-acetate-HPAM gel placed in open fractures, with emphasis on the effect of gel maturity at the time of placement. In field applications, gelant may partially or fully mature during pumping before reaching the fracture. Mature gel placed in open fractures yielded consistent, predictable rupture pressures following linear trends with placement rate and volume. Immature gel (gelant) gave comparable but less predictable rupture pressures; in some cores with Bentheim sandstone, gel failed to form due to rock-gelant interactions. Average permeability reduction was 5,000 for mature gel and 600 for gelant-treated cores. Placing gelant in both the fracture and adjacent matrix increased rupture resistance.

Key Takeaways

  • Mature gel placed in open fractures provides consistent, predictable rupture pressures following linear trends with placement rate and volume — a reliable, designable blockage performance for conformance control operations.
  • Immature gel (gelant) placed in fractures provides comparable initial rupture pressures but with less predictability — and in some cases failed to gel due to interactions between Bentheim sandstone and the gelant chemistry.
  • Average permeability reduction during subsequent waterflood was 5,000 for mature gel vs. 600 for in-situ crosslinked gelant — mature gel provides approximately 8x stronger long-term fracture blockage.
  • Placing gelant in both the fracture and the adjacent matrix increased rupture resistance compared to fracture-only placement — matrix gel provides additional resistance to fracture-flow bypass.
  • Rock-gelant chemical interactions in Bentheim sandstone prevented gelation entirely — confirming the need for compatibility testing between the specific gelant formulation and the target formation rock before any field application.
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