Currently, an oil well es produced until the economic limit had been gotten; after that if the oil prices are not sufficiently good to pay the oil value, the company choose to leave the well. But sometimes, after making reservoir studies the company rediscover a new potential zone that in the moment the oil price holds the spending.
In that cases, they choose to return into the oil well and making some operations called «Workover». The Workover consists in modify the situation of a reservoir as perforating new zones, isolating some water zones or maybe making a fish.
In the oil video we can see one way of carrying out the workover in an oil well made by Weatherford.