Abstract
Drilling of deeper oil wells goes hand in hand with more demanding requirements on completion materials due to, among other things, an ever increasing presence of CO2 and H2S. One of the solutions for meeting these challenges is the use of high alloy materials. Alloys with chromium content higher than 13 % chromium perform well in production fluids containing CO2 and H2S and as such are a common choice for tubing strings. However, non-production fluids associated with well operations are also handled through the same tubing. Therefore, it is necessary to know the behavior of these alloys vis-a-vis these other fluids. Acidizing operations are of particular concern when performed on wells completed with chromium alloys.
Lab tests were done on chromium alloys ranging from 13 % (Cr-Ni alloy) to 22 % Cr. The tests were run in the presence of different proportions of hydrochloric acid (10 -15 %), hydrofluoric acid (1.5 - 3 %), and acetic acid (10 %) and three commercial high temperature corrosion inhibitors. Metal losses in all cases were equal to or below 0.05 lb/sq.in. Nevertheless, some of the alloys showed considerable surface damage. This paper compares the behavior of several of these alloys in the presence of acidizing fluids, and illustrates the type of surface damage suffered by each alloy.
