Dispersants, aka dispersing agents, or friction reducing additives, are added to improve the flow properties of slurries. In oil field applications, dispersants are found in cement slurries, mud flushes, drilling fluids, fluids used in various transport applications, etc.

The mode of action of dispersants is by electrostatic repulsion or electrosteric repulsion. In a cement slurry for example, dispersants adsorb onto the cement particles causing the particle surfaces to be negatively charged and repel each other. This change in the surface charges of the cement particles and the subsequent repelling action results in desired rheological property changes. Dispersants provide the following benefits to cement slurries:

• Reduces slurry viscosity and reduces or prevents slurry gelation.
• Lowers the frictional pressures of cement slurries as it is being pumped into a well.
• Allows cement slurries with low water-to-cement ratios to have good rheological properties. This benefit is used to develop cement slurry designs that have slurry densities up to approximately 17 lbm/gal, without the need for heavyweight additives.
• Certain dispersants provide synergistic effects or behavior when used in combination with the following fluid loss additives in cement slurries: Hydroxyethyl Cellulose (HEC), Polyvinyl Alcohol, and certain AMPS based fluid loss additives.

The most common dispersant used in cement slurry systems is the sodium salt of Polynapthalene Sulfonate (PNS). Polynaphthalene sulfonates are polymers with molecular weights ranging from 3000 to 20000. Lignosulfonates with carboxylate groups also function to some extent as a dispersant in cement slurries, using a similar mechanism, it adsorbs onto the cement particles making them negatively charged, thereby resulting in electrostatic repulsion of the negatively charged particles which leads to dispersion. Hydroxycarboxylic acids, such as citric acid, can also be used as a dispersant in cement slurries, due to possibly the same mechanisms described above.

Olive & Branch M&D offers a high molecular weight polynaphthalene sulfonate, sodium salt that is a highly effective dispersant. Visit our Dispersant product page below to learn more about this product.