NACE SP0186-2024

This standard acknowledges procedures for the control of external corrosion of metallic well casings by applying CP. This standard is intended to be a guide for establishing minimum requirements for corrosion control when CP is practical and cost-effective.

External cathodic protection of external surfaces of uncoated or coated metallic (steel) well-casings directly impacts only the casing outer surfaces in direct contact with the borehole or through the cement (i.e., the cement used to fill the annular space between the borehole and the well-casing outer surface). Under some circumstances, external cathodic protection has been shown to reduce the prevalence of external corrosion on the inner (production) casing even when encapsulated in a multi string concentric well-casing assembly. External cathodic protection does not prevent internal corrosion of single or multi-string concentric well-casing assemblies.

This standard applies to all onshore and offshore “wells” with metallic (steel) casings. Included in this group are single or multi-phase production (oil, gas and water), reinjection (for product storage, product disposal, or reservoir maintenance), as well as geothermal wells. The basic CP principles for mitigation of external corrosion for all these types of wells are identical. In some situations (shallow water in particular) the offshore well casing may run through a metallic (steel) conductor that stretches between the platform and the seafloor. The encased portion of the well casing within the conductor does not receive CP, since it is shielded by the conductor pipe. The external water-wet surface of the conductor pipe is subject to corrosion and receives corrosion protection from the CP. Corrosion mitigation methods for the well casing section encapsulated within the conductor pipe are not discussed in this standard.