Plugs
Plugs are used during cementing operations to help remove dispersed mud (drilling fluid) and mud sheath from the casing inner diameter and minimize the contamination of cement. A bottom plug is pumped ahead of the cement slurry and behind the spacer. It wipes any remaining dispersed mud from the inner diameter of the casing as it moves down the string. When the bottom plug seats at the float collar, differential pressure ruptures a diaphragm on the plug, allowing cement to flow through, turn the corner at the bottom of the hole or toe end of a horizontal well and fill the annular space between the casing and the formation. Once the full volume of cement has been pumped, a top plug is dropped and pumped behind the slurry. The top plug wipes cement from the inner diameter of the casing and then seats at the float collar, resting on the bottom plug and causing a pressure increase at the surface indicating that the cement has been displaced. Top and bottom plugs are always different colors. Bottom plugs from Halliburton are red and top plugs are black.
