Patent ID: 7806180

Claim:
A method of extracting data from an existing well installation having a downhole metallic structure, which installation comprises an existing cable running from the surface to a downhole sensor unit at a downhole location, the cable being provided in the well installation for providing a communication path to the surface for readings taken by the downhole sensor unit, the downhole sensor unit being arranged so that the cable is electrically connectable to the downhole metallic structure of the well installation through the sensor unit, and the method comprising the steps of: operating on the downhole sensor unit to electrically connect the cable to the downhole metallic structure of the well; introducing a tool into the existing well installation for applying signals to the downhole metallic structure of the well; and applying signals, which encode data, to the metallic structure using the tool and extracting the encoded data at the surface by making a connection to the existing cable and sensing signals in the cable.