X-Ray Computed Microtomography Studies of Fluid Partitioning in Drainage and Imbibition Before and After Gel Placement: Disproportionate Permeability Reduction

R.S. Seright, Masa Prodanovic, W. Brent Lindquist – 2006

Abstract

X-ray computed microtomography (XMT) establishes that pore-filling Cr(III)-acetate-HPAM gels reduced water permeability to low values because water must flow through gel itself, while oil pressing on gel in Berea sandstone or porous polyethylene forced pathways by dehydrating the gel — leading to relatively high oil permeability. In very permeable sandpacks, ripping or extrusion mechanisms create oil pathways. XMT also reveals unexpected behavior in imbibition and drainage before gel placement: residual wetting-phase (water) saturations in Berea were surprisingly low in small pores, attributed to surface roughness from clay coating allowing efficient water drainage from small pores during oil injection.

Key Takeaways

  • Water must literally flow through gel to pass through gel-treated porous media — confirming that pore-filling gels create a genuine flow obstruction for water rather than merely redirecting flow around gel.
  • Oil pressing on gel in both water-wet Berea sandstone and oil-wet porous polyethylene creates oil flow pathways by dehydrating the gel — this dehydration mechanism explains why oil permeability recovers while water permeability remains low after gel placement.
  • In very permeable sandpacks, a different oil pathway mechanism operates — ripping or extrusion of gel by oil pressure rather than dehydration — showing that the dominant DPR mechanism varies with porous medium permeability and structure.
  • Unexpectedly, residual wetting-phase (water) saturations in Berea are lower than predicted in small pores — attributed to clay-coated pore wall roughness that allows efficient drainage of water films from small pores during oil injection.
  • The XMT study resolves imbibition and drainage behavior in both water-wet and oil-wet porous media as an important prelude to understanding gel behavior — the pre-gel fluid distributions determine what the gelant encounters during placement.
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