Tensile Testing of Casing Material at Elevated Temperatures Up to 550°C

Abstract

In high-temperature geothermal wells the casing is subjected to tremendous stresses and strains, particularly at temperatures above 200°C. When anchored to the formation or an external casing by cement, stress in the casing can easily exceed the yield stress locally. The associated plastic strain cycles during several well discharges can be such that the casing material properties deteriorates quickly and can lead to casing failure. Casing material data at such temperatures is not readily available for typical casing material candidates. Therefore, tensile tests were performed at room temperature, elevated (250°C) and high temperatures (450°C, 550°C) for the proposed material candidates (K55, L80, T95 and nickel-chromium alloy Inconel 625). The test series was conducted in the GeoWell project that was funded under the EU Horizon 2020 framework. Significant strength reductions with increasing temperature was observed. The test series results are in good agreement with design curves that are given up to 350°C in the New Zealand standard (NZS 2403:2015) with respect to the yield and tensile multiplication factors.