Titanium Alloy Casing for High Temperature Geothermal Field Application

Abstract

A new titanium alloy, Ti-3.6Nb-0.75Zr-0.2Ni has been developed for application in high temperature, high salinity and low pH geothermal wells. To se1ect the alloy composition, hot rolled and heat treated alloysamples were corrosion tested in a simulated geothermal brine. The final alloy composition was then extruded into casing pipe and corrosion tested in a laboratory flow through system at 180-350°C and 10 barg in a testing fluid containing H2S, CO2 and HCl as the corrosive species. The aim of testing setup was to simulate conditions in deep geothermal systems previously experienced in IDDP well in Krafla. The testing were conducted at three testing units connected in series; in the preheater where the rapid heating and boiling of the aqueous testing solution from RT to boiling and superheating of the fluid occurred, in the first reactor where superheated conditions are maintained at 350°C and lastly, in the second reactor where the temperature was set to 180°C or below the saturation temperature of the fluid to provoke condensation in the test chamber. This paper discusses the corrosion effects of the three conditions applied and how it compares to in-situ analysis performed previously at the IDDP-1 well. Microstructural and chemical composition analysis with SEM and EDS equipment were used for evaluating the corrosion resistance of the titanium alloy. The corrosion rate was also measured and compared to other CRA alloys. The results observed in the various testing conditions in the three flow-through units and the potential future application of the alloy for high temperature geothermal field application is also discussed.