Spacers and Chemical Wash

The main functions of a spacer are to separate the cement slurry from the drilling fluid, to assist in displacement of the drilling fluid, and to condition the walls of the wellbore for effective cement bonding.

To ensure the successful placement and ultimate zonal isolation of the cementing job, it is important to consider of a number of parameters such as drilling fluid condition, the presence of a good spacer, pipe movement, displacement velocity, slurry properties, pipe eccentricity and contact time. Good cement placement can only be achieved when all parameters are optimally fulfilled.

Spacers must be compatible with two fluids, the drilling fluids and the cement slurry. In general, these are very incompatible with each other.

Spacers are designed to work "chemically" with drilling fluids and cement slurries, still preventing  channeling between these fluids. When an oil based drilling fluid is used, it is imperative to ensure the wellbore is water wet.