Saudi Aramco Downhole Corrosion/Scaling Operational Experience and Challenges in HP/HT Gas Condensate Producers

Abstract

Abstract This paper shares Saudi Aramco's operational experience and challenges with downhole sweet and sour corrosion and scaling tendencies in the carbon steel (CS) completions. It also reports the company's approach to deal with these issues. Corrosion in wells drilled in sour gas bearing reservoirs commonly occurs in conjunction with iron sulfide scale deposits in the lowermost section of the production tubing and liner. Historically, the progression of sour corrosion has been relatively slow, so CS completions are cost-effective as the frequency of required workovers is low. Nevertheless, although scale deposits are not confirmed to curtail well productivity they reduce wellbore accessibility, which sometimes necessitates their removal by rig-less mechanical operation. Scale removal from old completions resulted in failure of the tubular integrity. In most sour gas wells corrosion starts posing scaling and obstruction problems inside the tubing far before any leaking risk. It is worth noting that this experience is consistent with field cases experienced by Total or other operators, as recently reported in the literature. The company experience with sweet gas producers have shown corrosion tendency to occur at shallow depths with no observed scale deposits. Corrosion was in the form of localized spaced scratches in the joints and metal loss in the pin- and box-ends. For these wells, the average life cycle of tubulars exceeds 10 years. The results from this field study might benefit the world gas producers of Saudi Aramco's intensive and diversified experience and of the completion practices that the company has adapted to develop the high temperature gas condensate fields. It is of particular interest to understand why the corrosion observed on these sweet wells is significantly lower than predicted by most carbon dioxide (CO2) corrosion prediction models.