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Role of colloidal polymer associates for the effectiveness of hydroxyethyl cellulose as a fluid loss control additive in oil well cement



The working mechanism of hydroxyethyl cellulose (HEC) as a fluid loss additive in oil well cement was investigated. The specific anionic charge amount, intrinsic viscosity, and associative behavior in a cement pore solution were determined. The fluid loss performance was probed through the static filtration of cement slurries. HEC achieves fluid loss control by reducing cement filtercake permeability. No influence on the filtercake microstructure was observed. ζ Potential measurements and a special filtration test indicated that no adsorption on cement occurred. Environmental scanning electron microscopy images revealed that in a wet environment, HEC swelled to a multiple of its size and possessed an enormous water-sorption capacity. Concentration-dependent measurements of the hydrodynamic diameter of HEC dissolved in a cement pore solution showed that large associates were formed. These colloidal associates physically obstructed the filtercake pores. Finally, the addition of sulfonated melamine formaldehyde dispersant to the cement slurries containing HEC greatly improved the fluid loss control. A specific interaction was responsible for this synergistic effect. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012