Corrosion Control in Gas-Lift Wells^⋆

Severe corrosion was found to be taking place in the South Texas oil wells where producing pressures were not abnormally high. Most of these wells were produced by gas lift. An investigation was instigated to study the causes of the corrosion and find some means of bringing it under control. An Otis type “F” tubing stop was developed to hold a specially designed coupon so that the corrosion rates could be checked at various levels in the tubing. The studies indicated that the rates of corrosion followed the general corrosive criteria set up for condensate wells when the pressure conditions at given depths and temperatures and CO², contents were considered. The top-hole coupons did not reflect the actual severity of corrosion which could be taking place down the hole in the same manner as they do in condensate wells. It was also found that in these gas-lift wells a considerable height of water column was present in the annular space, and any successful inhibition method had to be so designed that the inhibitor would mix in the water and diffuse through it to fall to the bottom. Oil soluble and emulsifiable inhibitors were therefore found to be unsatisfactory, because they were blown through the gas-lift valves and never reached the bottom of the tubing. General factors governing corrosion mitigation problems in these oil wells are discussed.