This paper will discuss various design issues with well casing Cathodic Protection - CP. In addition, the benefits of CP for well casings and what determines the need for well casing CP will be discussed. Finally, a case history dealing with design issues and what solutions were available and utilized.
The use of cathodic protection - CP for protecting the external steel surfaces of well casings is a proven technique to reduce or minimize external corrosion. Production wells and storage wells utilize cathodic protection and it is quite successful in stopping or minimizing external corrosion. The need for CP on well casings does depend on many factors, primarily economics, corrosive electrolyte in contact with the casing, corrosion cells - long line and localized and stray current interference. The goal of installing CP for well casings is to prevent casing leaks.
Note: When discussing ”well casing” we include the external surfaces of the surface casing, casing and production tubing in the total circuit.
Cathodic protection has been used for protecting well casings from external corrosion for decades. The process is simple but the application can be complex. The primary purpose is to prevent casing leaks. A casing leak on a production or storage well is an expensive repair that can be minimized via the application of CP.
Economics: The primary reason for most owner/operators is economical. Every well has a design life and depending on the life, the time to leak is determined and if less than the design life - installing CP becomes economical as it will prevent leaks for the design life of the well. If the well has a finite life and the time to leak is greater than the finite life then CP may not be necessary. The issue is most wells are run beyond their design life and enter the time to leak zone. Many owner/operators realize this or operate storage wells which have a long life well beyond the predicted time to leak and CP becomes a viable economic option.