Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. More information
A short piece of casing run one to two joints above the end of casing. The collar contains a backpressure or check valve which stops cement from reentering the well after displacement into the annulus. It is useful to prevent channels in the cement until the cement is set.