Is the first operation required to complete the well after the hole has been drilled, logged and tested. Its purpose is to prevent the wall of the hole from caving in and to provide means of extracting petroleum if the well is produced.
As mentioned earlier, the purpose of casing is to cover the formations that are penetrated. This keeps the borehole walls from caving in and prevents communication between different formations: the ones that have been cased and the ones that are going to be drilled.