Gel Dehydration by Spontaneous Imbibition of Brine From Aged Polymer Gel

B. Brattekås, Å. Haugen, A. Graue, and R.S. Seright – 2014

Abstract

This work investigates dehydration of Cr(III)-acetate-HPAM gel by capillary imbibition of water from gel into strongly water-wet chalk matrix. In fractured chalk reservoirs, spontaneous imbibition of water from fracture-filling gel into oil-saturated matrix causes gel shrinkage, potentially reopening gel-filled fractures to flow. Spontaneous imbibition rate was much slower from gel than from brine, and decreased with increasing matrix-volume-to-open-face ratio. A dehydrated gel layer on the core surface lowered subsequent imbibition rate. Severe dehydration and gel shrinkage up to 99% volume were observed, suggesting gel treatments may lose efficiency over time wherever significant imbibition potential exists.

Key Takeaways

  • Spontaneous imbibition of water from gel into strongly water-wet chalk matrix causes severe gel dehydration and shrinkage — up to 99% volume reduction observed — potentially reopening gel-filled fractures to flow over time.
  • SI rate from gel is significantly slower than from brine — the gel polymer network restricts water mobility — but dehydration continues until severe shrinkage occurs given sufficient time and contact area.
  • SI rate decreases with increasing matrix-volume-to-open-surface ratio — large matrix blocks with limited gel contact area dehydrate gel more slowly than small plugs with high surface-to-volume ratio.
  • A dehydrated gel layer forms on the core surface and acts as a barrier that progressively reduces the SI rate — an auto-limiting but not self-stopping process: severe dehydration still occurs over time.
  • Field gel treatments in water-wet fractured chalk reservoirs face long-term efficiency loss from SI-driven gel dehydration — treatment design should account for potential gel volume reduction over the project life.
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