A software program for selecting an optimum tubing material has been developed from the viewpoints of corrosion resistance and economical efficiency. This software has made it possible to compute the distribution of pH and other indexes of environmental severity in the well-depth direction, which are needed for the estimation of corrosion characteristics. Based on the results of computing, it has also been made possible to estimate corrosion characteristics of various materials at a specified well depth. Further, by applying this software, it is now possible to design a mixed string in which a higher-quality material is arranged in a severe depth region and a lower- quality material in a mild
depth region. Keywords: Material Selection, Tubing, Corrosion, Software Program, Mixed String