Since casing strings are cemented in place, this is significantly more difficult and expensive than replacing the completion string. If in some instances the casing string cannot be removed from the well, it may be necessary to sidetrack the offending area and recomplete, which is also an expensive process.
Because casing strings are set in place permanently, this approach is significantly more complicated and costly than replacing the completion string. In certain situations, if the casing string cannot be removed from the well, it may necessitate diverting around the problematic area and reworking, which is also a pricey undertaking.