Let's say you have 4000 meters of casing in place. You run the pressure tests, and your numbers are just not right. You go through the procedures again, but the deviation is still there. How can you tell wich of the several hundred connections causing the casing leak? Is it the one on 150 meters, or the one on 3750 meters? It is a guessing game, and your only option is to pull the whole casing. Or, is it?