Oil-well cementing is the process of pumping cement slurry down the annulus between the casing and wellbore. This is known as the primary cementing. The objective is to form a cement sheath that will ensure zonal isolation, support, and protect the casing.
A device fitted to the top joint of a casing string to hold a cement plug before it is pumped down the casing during the cementing operation. In most operations, a bottom plug is launched before the spacer or cement slurry. The top plug is released from the cement head after the spacer fluid.