Pore-Level Examination of Gel Destruction During Oil Flow

R.S. Seright, W. Brent Lindquist, Rong Cai

Abstract

Pore-scale XMT images track oil and water saturations in individual pores as a function of oil throughput after pore-filling Cr(III)-acetate-HPAM gel placement, in both water-wet Berea sandstone and hydrophobic porous polyethylene. In hydrophobic polyethylene, oil saturations increased and gel was destroyed quickly in the smallest and largest pores, but most slowly in intermediate-size pores — suggesting a balance between gel dehydration by oil film growth versus gel extrusion. In water-wet Berea, oil saturation increased evenly across all pore sizes — consistent with imbibition behavior before gel placement, suggesting oil had uniform access to Berea pores of all sizes and uniformly dehydrated gel. Gel extrusion did not appear significant in Berea.

Key Takeaways

  • In hydrophobic porous polyethylene, gel destruction during oil flow proceeds fastest in the smallest and largest pores but slowest in intermediate-size pores — indicating a competition between gel dehydration (dominant in small pores) and gel extrusion (dominant in large pores).
  • In water-wet Berea sandstone, oil saturation increases evenly across all pore sizes after gel placement — consistent with oil having uniform pore access (the same as before gel) and uniformly dehydrating gel throughout the pore network.
  • Gel extrusion (physical displacement of gel mass) is not significant in Berea sandstone — dehydration is the dominant mechanism for oil pathway creation in water-wet sandstone at Berea permeabilities.
  • The pore-size-dependent kinetics of gel destruction in hydrophobic polyethylene reveal that the DPR treatment’s durability depends on how quickly oil can dehydrate or extrude gel in pores of different sizes — a predictive insight for treatment longevity assessment.
  • These pore-level results establish the physical basis for predicting cleanup times for gel-treated oil zones — directly supporting the mobility-ratio model for oil zone cleanup time presented in the companion Seright cleanup paper.
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