Definition - What does Cement Plug mean?
A cement plug is a rubber plug that is used to separate cement slurry from mixing with other fluids. This reduces contamination and maintains the consistency of the slurry. Proper placing of cement plug minimizes material wastage and wasted rig time. Cement plugs are of two types: the bottom cementing plug and the top cementing plug.
Trenchlesspedia explains Cement Plug
The bottom cementing plug has a diaphragm in the body that ruptures to allow the cement slurry to pass through once the plug arrives at the landing collar, and It is inserted before pouring the cement slurry to reduce the chances of contamination by fluids present in the casing. The top cementing plug has a solid body which gives confirmation of contact with the bottom plug and landing collar indicated by an increase in pump pressure.
Cement plugs are used for a variety of purposes. Lost circulation issues are solved by detecting the cement plug and drilling back through it. When a well has to be remedied or abandoned or zones have to be plugged, cement plugs are used to seal off selected intervals, dry wells, depleted holes.
It's also used to begin directional drilling by guiding the drill bit in the correct direction. When a test zone is quiet off bottom, a cement plug provides an anchor to perform an openhole test.