Cementing the Wellbore: Cementing Operations (Part 2)

A steel pipe, or casing, is run into the wellbore before an L-shaped cementing head is fixed on top of the wellhead to receive the slurry. Two wiper plugs, the top and bottom plugs, sweep the inside of the casing and prevent the slurry and drilling fluids from mixing.

The bottom plug is introduced into the well before the slurry is pumped into the well behind it. The bottom plug, which works as a one-way valve that allows the slurry to enter the well, is caught just above the bottom of the wellbore by the float collar.

As cement is pumped into the wellbore, pressure is increased until a diaphragm is broken within the bottom plug. This allows the cement to flow through the casing and up outside the casing string. After the proper volume of slurry is pumped, a top plug is pumped into the casing to push the remaining slurry through the bottom plug. The pumps are turned off once the two pumps reach each other, and the slurry is allowed to set.

Pumpability time is the amount of time it takes for the slurry to set. Special types of cement are used to set wellbores at deep depths, under high temperature and pressure, and in corrosive environments.

“How Does Cementing Work?” Rigzone. Dice Holdingd, Inc., 1999. Web. 19 Dec. 2014. <https://www.rigzone.com/training/insight.asp?insight_id=317&c_id=1>.