Further Investigations on Two-Phase Flow Property Modification by Polymers: Wettability Effects.

Abstract

Abstract Adsorption of water-soluble polymers in porous rocks is known to reduce water permeability much more than oil permeability. This effect is often referred to as "Disproportionate Permeability Reduction" (DPR) and can be used in production well treatment to reduce the water cut. This paper deals with nonionic polyacrylamide adsorption on carbonate rocks having different wettability properties. Cores were used first in their native water-wet condition, and after a wettability modification, which was obtained by aging cores saturated with a polar crude oil at 60°C for 6 weeks. Efficiency of the treatment was attested and quantified by strong changes in the wettability index as measured using Amott tests. Drainage and imbibition cycles were performed on these carbonate samples before and after polymer treatment. Polymer adsorption and oil/water relative permeabilities were compared for both media. While the quantity of adsorbed polymer is almost the same on water-wet and on wettability-modified cores, adsorption rates, estimated from viscosity profiles of effluents, are significantly different, suggesting that the polymer slowly restores part of the water-wet character of the native core. All our results indicate that polyacrylamide adsorbs on the rock whatever being the wetting conditions. While disproportionate permeability reduction is always observed, DPR is greater in low-permeability cores.