Spacers and Flushes
One of the keys to successfully achieving zonal isolation is preparing the wellbore to receive cement. This is done by using spacers to fully displace drilling fluid from the annulus and condition the casing and annular surface to accept a cement bond. Spacers and flushes are intended to displace drilling fluid from the annulus, leave the casing and formation water-wet (free of oil), and separate drilling fluids from the cement slurry. Thus, the spacer is pumped ahead of the lead cement slurry. Flushes are used to thin and disperse drilling-fluid particles.
If even a thin layer of oil from the drilling fluid is left on the casing and/or the formation it can prevent the cement slurry from directly contacting each surface to form a good bond. A properly conditioned hole has the best chance for a good cement job and the least chance of annular gas migration problems or costly remediation and squeeze cement operations.
The performance of a spacer mainly depends on
- The rheology of spacer at the desired elevated temperature;
- The compatibility of the spacer with the drilling fluid (mud) and the cement;
- The volume of spacer necessary to provide sufficient separation of the cement from the mud to prevent the cement from becoming contaminated by the drilling fluid;
- Contact time and pump rate of the spacer to optimize drilling fluid displacement and removal.
Halliburton offers spacers and flushes to help operators improve the probability of returning uncontaminated mud to the surface and securing a successful primary cement job.