Definition - What does Cementation mean?
Cementation is the process of binding things together through the use of cement. The process starts with making slurry by mixing cement and water and pouring it at the desired place to get hardened and hold things in place. Cementation in an oil well is done by pouring cement to an adequate depth/ length along the pipe to hold the casing pipe in its position.
Petropedia explains Cementation
In oil and gas well drilling, a well is completed in stages where suitable size casing pipes are lowered at each stage. Well cementing is done at each stage so as to hold the casing pipe in its position. The slurry of cement and water is mixed in desired density and pumped down the well in the annulus. The drilling of an oil well often leads to cracks and fissures beneath the earth's surface. In order to prevent the drilling fluids, oil and natural gas from seeping through these cracks and getting lost, the space between the well walls and the casing is sealed using a cement slurry. The cement also protects the casing from corrosion, shocks etc.