Fluid loss control agent is used in the cement slurry to maintain the water / solid ratio unchanged. This is achieved by controlling the filtration rate of water in the cement slurry into the adjacent permeable zone.

 

The use of fluid loss additives helps prevent:

 

- premature dehydration of cement slurry, resulting in annulus blockage and failure to complete injection operation.

 

- the fluidity of cement slurry changes, which reduces the efficiency of replacing mud slurry.

 

- cement slurry filtrate damages the mining layer.

 

There are several viewpoints on the action mechanism of fluid loss additive: 1. improve the viscosity of cement slurry to make it unsuitable for dehydration  2.Increase the static shear force of cement slurry, and gelling occurs once it is still, which neither generates static pressure nor transmits external pressure  3.Granular materials with different particle size distribution block formation voids or micropores  4.The water-soluble polymer is adsorbed on the surface of cement particles to form an adsorption hydration layer, resulting in the bridging of cement particles, resulting in a network structure, binding more free water, blocking the internal voids of cement and reducing the permeability of cement filter cake. According to this principle, there are only two kinds of fluid loss additive for oil well cement: solid particle material and water-soluble polymer.