Detailed explanation of corrosion in oil and gas extraction

Corrosion in oil and gas extraction can be divided into:

Chemical corrosion: mainly occurs during the construction process of oil and gas extraction, such as acidification, fracturing, cleaning of pipelines and large tanks, etc.

Electrochemical corrosion: Electrochemical corrosion is the main form of corrosion in oil and gas extraction. Petroleum pipelines, downhole casing, oil pipes, pumping rods, and their downhole tools are in long-term contact with soil, well fluids, natural gas, and formation water (seawater). The differences in the types of metals used, organization, crystallization direction, internal stress, external force, surface smoothness, and surface treatment conditions, as well as the types of electrolytes in contact with different parts of metals The differences in concentration, temperature, flow rate, etc. result in numerous anode and cathode areas appearing on the metal surface. The anode and cathode areas form corrosion batteries through the closure of the metal itself. Different wellbore structures have different macroscopic and microscopic corrosion batteries due to the different strata, well fluid electrolytes, and water content in contact with each other.

Electrochemical corrosion in oil and gas extraction is the most complex and unique type of corrosion among all metals.

Hydrogen sulfide corrosion: Hydrogen sulfide aqueous solution is weakly acidic and contains H+, HS -, S2-, and H2S molecules. It exhibits hydrogen depolarization corrosion, generating iron sulfide. The adsorbed HS - causes the metal potential to shift towards negative values, accelerating the anodic process and accelerating the electrochemical corrosion of the metal. The generated black layer of iron sulfide (Fe9S8) forms a corrosion cell with the steel. Iron sulfide (Fe9S8) is a strong reducing agent in the corrosion cell, and the steel is the anode. Iron sulfide is the cathode, which makes the corrosion rate several times higher than that of the uncovered area, forming a typical scale corrosion. H2S can also cause various types of corrosion in steel, such as hydrogen embrittlement and sulfide stress corrosion cracking.

Carbon dioxide corrosion: Carbon dioxide corrosion is a corrosive medium for non sulfur-containing oil and gas fields. Carbon dioxide dissolves in water to form carbonic acid, which produces hydrogen depolarization corrosion on steel. For sulfur-containing wells, carbon dioxide accelerates the corrosion of metals by hydrogen sulfide.

Oxygen corrosion: Oxygen corrosion is the most common type of oxygen corrosion, which produces oxygen depolarization corrosion and oxygen concentration corrosion on pipelines, storage tanks, etc. of oil and natural gas.

Atmospheric corrosion: Oxygen depolarization corrosion caused by the influence of oxygen, water vapor, etc. on pipelines, storage tanks, etc. exposed to the atmosphere.

Soil corrosion: The electrochemical corrosion formed by the casing of oil and gas wells passing through different layers of the formation and coming into contact with different electrolytes such as soil, rock layers, water layers, and salt layers.

Bacterial corrosion: The most typical bacterial corrosion in oil and gas extraction is sulfate anaerobic bacterial corrosion.