インヒビター処理による13%Cr鋼チュービングの腐食の軽減

抄録

In order to extend the service lives of corroded 13%Cr steel tubing strings, batch treatment of corrosion inhibitor was considered. However, there was no inhibitor for chromium containing steels. As a result, the candidate inhibitors recommended by leading chemical suppliers were inhibitors suitable for carbon steel in hot, CO₂ environments. The inhibitors were evaluated for their adsorption behavior and film persistency not only for bare 13%Cr steel but also for corroded one. Judging from the estimated corrosion mechanisms, water displacement ability of an inhibitor from corrosion pits and other corrosion products were considered to be very important. Therefore, the water displacement ability and the ability for making the corrosion products oil-wet were also evaluated in the laboratory.
The selected inhibitor from the series of laboratory tests was served for a field test. A well was inhibited by a spire-headed tubing displacement method. The inhibitory effect on the corrosion was monitored by iron counts in produced water. After the tubing inhibition, the iron counts stayed low for fifty days, then gradually rose and returned to its original figure at three months after the tubing inhibition. This treatment life was much longer than we had expected, and that length could not be explained by the conventional adsorption theory. The inhibitor's ability of water displacement and making the corrosion products oil-wet was considered to play very important roles in this very long treatment life.
In addition to the abovementioned new findings, very important mechanistic information was reconfirmed in the series of laboratory tests. The additional inhibitory effect of liquid hydrocarbon is very important, sometimes much larger than that of inhibitor itself, from the stand point of the degree of inhibition.