Working mechanism of poly(vinyl alcohol) cement fluid loss additive

Abstract

Abstract The working mechanism of poly(vinyl alcohol) (PVA, M w ∼ 200,000 g mol −1 ), a fluid loss control additive (FLA) applied in oil well cementing, was investigated. First, characteristic properties of PVA such as solubility and particle size in cold and hot water, minimum film forming temperature, adsorption on cement, viscosity of cement pore solution and static filtration properties of cement slurries treated with PVA were determined. It was found that the working mechanism of PVA relies on hydrated, but water‐insoluble PVA particles (d 50 ∼ 2.4 μm). During cement slurry filtration, they coalesce into a polymer film. This film effectively plugs the pores of the cement filter cake. The sample studied here becomes water‐soluble at temperatures > 40°C (d 50 decreases to ∼50 nm) and looses its effectiveness. Addition of highly anionic dispersants such as ß‐naphthalenesulfonate formaldehyde (BNS) or acetone formaldehyde sulfite (AFS) polycondensate extends the temperature range at which PVA works from 40°C to ∼60°C. This effect is ascribed to lower solubility of PVA in the presence of these dispersants. The study reveals that decreased performance of PVA caused by higher temperatures is not the result of thermal degradation of the polymer, but is owed to its increasing water‐solubility. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010