Corrosion Behavior for Casing in Producing Well with Water Injection Technology during Long-Term Service

Corrosion leakage became serious due to cyclic sewage injection and continuous increase in water injection pressure. Corrosion behavior for N80 casing was studied during long-term service, using corrosion reaction kettle and weight loss method. The morphology and composition were characterized with laser confocal microscopy (LCM), scan electron microscopy (SEM) and energy disperse spectroscopy (EDS). These results showed that corrosion rate remained constantly at initial stage, and increased gradually, then sharply reached to 0.327mm/a at later stage, accompanying with inflection point under oxygen condition. Meanwhile, corrosion rate decreased significantly from 0.028mm/a to 0.020mm/a under oxygen-free condition. The corrosion of N80 steel was dominated by dissolved oxygen, and accelerated by chloridion. The micro-mechanism was suggested to be the transition of defect structure from crack with micron range to etch pit with millimeter range.