Dispersants
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Successful
cementing relies on good mud removal, which is best achieved by pumping the
cement slurry in turbulent flow. Dispersants control slurry rheology and help
induce turbulence at low pumping rates. Dispersants also allow the water content
of the cement to be lowered without making it difficult to pump.
Basically,
dispersants neutralize positive charges on cement particles, which would
otherwise make them mutually attractive. They effectively break up aggregates
into individual particles. At the right concentration, dispersants improve
cement homogeneity and lower its permeability. However, an overdose of
dispersants can produce a phase separation in the cement slurry that results in
cement particles settling out of solution and the development of free water. The
most common dispersants are sulfonates containing highly branched polymers.
Polynapthalene sulfonate is the most widely used.
