Corrosion Treatment Programs

The Bakken Formation is among the largest connecting deposits of oil and natural gas in the United States. There are two primary corrosion treatment programs that are designed to prevent corrosion that could lead to tube failure, including localized corrosion and erosion corrosion.

Localized Corrosion

Localized corrosion, or pitting corrosion, can be identified easily by the formation of pits on the surface. These pits are formed when dissolved gasses, such as carbon dioxide or hydrogen sulfide are absorbed into the surface of the tube, forming a large cathode. In an area that is smaller by comparison where the gases are not absorbed, there is a lower potential, thus an anode is formed.

Electrons will flow from the anode over to the cathode. Since the cathode is large and the anode is small, the flux of electrons will be remarkably high. When the electrons quickly leave the anode, it releases iron. The result is a highly localized loss of metal.

Erosion Corrosion

Erosion corrosion is mostly due to multi-phase flow. The greatest cause for concern is when the pressure drop causes dissolved gases to be released rapidly. During the transition from one phase to another, the dissolved gasses will expand in volume.

When drops in pressure occur, super-saturated brine crystallizes salt. This leads to deposits where sodium chloride forms on the nozzles and other components. In addition, abrasive crystals and other insoluble particles develop in the formation fluid.

When multi-phase flow takes place, protective films that slow corrosion is removed, and the metal surfaces are exposed to a highly corrosive environment. Failing to repair the protective film quickly, the tube could fail rapidly well before normal life expectancy under the combined effects of localized pitting corrosion and erosion corrosion.