Well monitoring

A method for detecting the level of water in a formation associated with a well, comprising:

• using signals received from a well installation, the well installation comprising tubing having an extension portion extending to a depth beyond that required for extraction of product;
• and
• detecting, from the received signals, the level of water in the formation associated with the well.

A surface unit for detecting a level of water in a formation associated with a well, which well includes a well head, the surface unit comprising:

• a receiver configured to receive signals from tubing, the tubing comprising an extension portion extending to a depth beyond that required for extraction of at least one product from the well;
• and
• an evaluation unit configured to detect the level of water in the formation from received signals having been received at the receiver and having been influenced by signals in the extension portion.