Potential profiles taken of 9⅝ inch gas well casing at the Lacq Field in south-western France were evaluated to determine the correlation between current discharge zones and. geological formations. At the same time an effort was made to distinguish between galvanic currents and stray current originating from an electric railway traversing the field. Estimates of the general electrical conformation of the field were deduced from data collected on a few wells.
Numerous conventional methods were considered in attempting to fix the optimum current, density to be applied to each casing. Cathodic protection currents varied in volume from 15 to 50 amperes, so ground beds of varying configurations were used, including 50 meters of pipe horizontally in a conductive zone and 50-meter vertical holes.
An investigation is under way to determine what benefits can be obtained by altering the existing electrical configuration resulting from the electric railway stray currents. This will be accomplished by modifications at a substation and possibly by using the pipeline grid as a low-resistance drainage return. There is some concern that cathodic protection may produce local cells whose effect seems to be as severe as the galvanic currents normally existing. 5.2.4
