Paper: Corrosion Characteristics And Control In Deep, Hot Gas Wells

For the purposes of this paper, deep, hot gas wells will be considered to be those that fall within the following ranges of conditions: Deeper than 10,000 feet; hotter than 2000F bottomhole temperature (BHT); and bottomhole pressure (BHP) higher than 5,000 psi. Corrosive wells also contain an aggressive acid gas (H2S or C02) in amounts of 0.1% or greater. In addition, water production considerably aggravates corrosion especially if it is a heavy brine. When corrosion is observed, it is found to occur anywhere between the bottom and top of the hole, sometimes even continuously from bottom to top of the hole; rarely ever concentrated in just the top 2,000 or 3,000 feet which is normal for gas condensate wells. In general, the rate of corrosion is aggravated by increasing partial pressure of CO2 or of H2S. In some pure CO2 systems (H2S free), a passivation effect is observed when especially pure water and high pressure/temperature conditions are realized. However, even very small amounts of H2S (ppm's in the gas phase composition) can cause activation of the corrosion due to CO2 which affects the passivation effect. Corrosion rate is also aggravated by increases in temperature, in water production rate, and especially by the production of heavy brines. Heavy brine production indicates that a considerable volume of aqueous electrolyte is contained in the hole in contact with the CO2 or H2S and thereby causes considerable aggravation in both the area of steel which is corroding as well as the rate of corrosion.