Polymer Adsorption/Retention in Porous Media: Effects of Core Wettability on Residual Oil
Daniel Broseta (Inst. Francais du Petrole) | Fatiha Medjahed (Inst. Francais du Petrole) | Jacqueline Lecourtier (Inst. Francais du Petrole) | Michel Robin (Inst. Francais du Petrole)
Low polymer retention in the reservoir is essential to the success of a polymer EOR operation. It is usually estimated from laboratory core flood experiments conducted under conditions as. close as possible to those prevailing in the field. This work addresses the effects of core meltability and oil saturation on polymer adsorption/retention.
Adsorption of water-soluble polymers onto oil or, more generally, hydrophobic substrates, is characterized from a series of core flood experiments on siliceous and (otherwise similar) alkane-coated substrates. It is found that, for the most common EOR polymers, adsorption increases with surface hydrophobicity, the effect being stronger for neutral synthetic polymers (polyacrylamide) and polysaccharides (scleroglucan and xanthan) than for anionic synthetic polymers (hydrolyzed polyacrylamide).
In a second series of core flood experiments, polyacrylamide adsorption/retention in cores under residual oil saturation is measured and compared to the adsorption/retention in similar oil-free, 100% brine saturated, cores. In oil-wet cores, retention decreases considerably in presence of oil, while it slightly increases in water-wet systems.
These effects may be explained in terms of water/rock and water/oil interfacial area distribution within the pore space, which is governed by wettability. In water-wet cores, droplets of residual oil offer an additional adsorbing surface to the polymer, whereas in oil-wet cores the oil wetting film offers to the polymer a small adsorbing surface compared to the no longer accessible rock surface.
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