Cathodic protection for casing in oil and gas Wells

The so-called cathodic protection is to be protected metal through a certain direct current, so that the metal to be protected as a cathode and be protected. According to the different ways of providing current, it can be divided into sacrificial anode protection and impressed current protection.

Sacrificial anode protection is a method of selecting a metal material with a lower potential, connecting it with the protecting metal in the electrolyte, and protecting other metals by relying on the current generated by its corrosion. A metal or alloy that dissolves itself in order to protect other metals is called a sacrificial anode. Commonly used are aluminum alloy, zinc alloy, magnesium alloy and so on.

Impressed current cathodic protection is to provide the required protection current by an applied power source. A method of protecting the protected metal by using the protected metal as the cathode and a specific material as the auxiliary anode.

Because the casing of steam injection well goes hundreds to thousands of meters underground, and the outer surface of the casing is often not coated with insulation anticorrosive layer, the cathodic protection current required is very large, so the application of sacrifice anode is limited, and the applied current cathodic protection should be used. In the cathodic protection system, the position of the anode ground bed has a great influence on the distribution of cathodic protection current and potential on the sleeve:

According to the previous research results shown in FIG. 1, 2 and 3, the far anode ground bed and deep anode ground bed will expand the transmission range of cathodic protection current and help to make the cathodic protection potential of the whole casing meet the technical requirements. In addition, the deep anode ground bed reduces the possible disturbance to surface metal structures. Due to the density of oil and water Wells and the small distance between Wells in some areas, the use of the far anode ground bed will be limited to a certain extent. Therefore, for the impressed current cathodic protection of oil and water well or steam injection well casing, the anodic ground bed of deep well is buried, which can not only increase the uniformity of protection potential of steam injection well casing, but also avoid interference to other objects.