Cathodic Protection for Internal Surface of Water Well Casings

I was asked recently if cathodic protection can be used to protect the internal surfaces of a water well casing.

Although cathodic protection is used to protect the external surface of water, oil production well casings, and natural gas well casings; it is not standard practice to use cathodic protection inside a water well casings.

I was project engineer for a experimental project to use cathodic protection to protect the internal surfaces of a water well casing.  Special magnesium anodes had to be made that were small enough to fit inside the well casing.  A permanent reference cell was put inside the well casing and it's wire connection mounted inside a test station near the water well. 

The result was the cathodic protection was effective in protecting the water well when the pump was not running.  Since cathodic protection current requirements are a function of water velocity, the water well didn't have sufficient cathodic protection levels when the pump was operating.  However, internal corrosion of water wells tend to occur mostly when the water well is idle.