Corrosion Influencing Factors of Sour Gas Wells in Chuandongbei, China

Because of the high downhole pressure environment in the Chuandongbei gas field (8 to 17% [v/v] of hydrogen sulfide [H2S] content and 5 to 10% [v/v] of carbon dioxide [CO2]), a study was made of the behavior of corrosion-influencing factors on AC80 steel used for downhole tubing. The results show that AC80 is corroded severely by the downhole environment, with a corrosion rate of 0.273 to 2.677 mm/y. The H2S and CO2 partial pressure, the Cl− content in the water, and the presence of sulfur are the main factors that affect the corrosion of the steel. The corrosion rate reaches its maximum when the temperature is 40°C, but changes slightly when the temperature is 60 and 120°C. The corrosion rate increases gradually with increasing Cl− content in the water, or from the partial pressure of H2S and CO2. The presence of elemental sulfur will accelerate the general and pitting corrosion of AC80 and the maximum pitting corrosion depth is 41.4 mm/y. The corrosion products are ferrous sulfide (FeS) and FeS09.