Drilling Industry Glossary

Micro-annulus

During cementing job, if the displacing fluid (cement slurry) fails to completely remove mud and/or spacer, a small layer of the mud and/or spacer remains on the walls of the annulus or the formation. Once the cement sets, the space occupied by the small layer of mud and/or spacer can lead to the creation of a "micro-annulus". It normally occurs on the narrow side of the annulus.