CORROSION CONTROL IN GERMAN GAS-WELLS

Natural gas wells in West Germany producing from 1100 ft at 149 C are attacked by the combined effects of carbon dioxide (up to 50%) as well as sulfur and hydrogen sulfide. Inhibited water and packer muds are used in sweet gas wells. Wet carbon dioxide causes pitting and surface attack at pressures as low as 7 psi and Mg or calcium chloride deposits with less than 2 pH are encountered. Galvanic attack is a major problem. Some wells have been blocked by salts or carbonates for which acid cleaning is only partly effective. Elemental sulfur deposits in some wells are scraped off and a solvent is continuously applied in others. Continuous inhibition which is necessary in high pressure wells often is applied using coiled tubing as an injection string. Steel is heat treated to resist attack, but inhibition is the most effective control measure. Amines are most commonly used inhibitors, but ammonia and inorganics including arsenic have been tried. Chemical analyses, coupons, electrical resistance probes, caliper surveys, and electromagnetic detectors are all used.