Abstract
A detailed review is made over 125 distinct field cases of sour weight loss corrosion (SWLC), i.e. all uniform and localized corrosion types out of any cracking, on oil and gas wells, lines and process facilities, covering nearly 45 distinct fields/ reservoirs.
The fluid corrosiveness is classified in 3 categories, from a negligible corrosiveness in 40 to 50% of the cases (both in oil and gas production), to a moderate attack (typically within 1 mm/yr) in most of other cases and lastly to a very severe corrosion in a few cases. Although quite rare, these severe corrosion cases are impressive as corrosion rates are currently above 10 mm/yr, even in apparently mild conditions. Interesting enough is the fact that these 3 categories seem to correspond to 3 distinct corrosion mechanisms.
Leading and secondary corrosion factors are sorted out from this analysis. The flow velocity and flow regime are shown to be the most leading factors of the transition between negligible and intermediate and severe corrosion categories. It is also highlighted that very severe corrosion cases require "pit promoters" (sulfur, oxygen, bacteria…) and a galvanic effect with surrounding non corroding surfaces. It appears from reviewed experience that these promoters are mostly extraneous to produced fluids, apart from sulfur depositing from sour gases.
It is worth noting that most factors have a similar corrosion contribution in oil as in gas production systems, in wells as in lines. This suggests that the basic corrosion mechanisms involved on these different facilities are not so different.
Preliminary indications are given on possible corrosion mechanisms involved in the 3 corrosion categories. Research and Development (R&D) studies recently launched around the world on H2S corrosion are thus strongly encouraged to study and challenge these proposed mechanisms. They are also welcomed to take as much benefit as possible of the reported experience.
