04/08/2023
Well Cementing Fundamentals
Basic two-plug primary cementing operation. After a well interval has been drilled to the desired depth, the drillpipe is removed and a casing string is lowered to the bottom of the borehole (top). The bottom of the casing string is usually fitted with a protective shoe, and centralizers keep the casing centered in the wellbore. Engineers pump chemical washes and spacer fluids down the casing interior, thereby displacing drilling fluids (middle left). They next insert a bottom plug, followed by a volume of cement slurry that is sufficient to fill the annulus (middle right). Continued pumping of cement slurry forces drilling fluid out of the casing interior, up the annulus and out of the wellbore. When the bottom plug lands at the bottom of the casing string, a membrane in the plug ruptures, opening a pathway for the cement slurry to enter the annulus. Engineers insert a top plug after the cement slurry, and the top plug is then followed by a displacement fluid (bottom left). Pumping the displacement fluid forces the top plug downward until it lands on the bottom plug, thereby isolating the casing interior and annulus and filling the annulus with cement slurry (bottom right).
