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With recent increasing interest in drilling deep geothermal wells in order to produce from higher enthalpy heat sources than before, the strength of the casing becomes one of the most limiting factors. Casing failures include collapse or partial collapse (bulges) and tensile ruptures if wells are allowed to cool down or are killed by pumping water into them. Structural impact of large temperature and pressure changes remains one of the challenges to be solved for utilization of deep geothermal wells. Thermal expansion of materials, degradation of structural properties at elevated temperatures, corrosion and cyclic loads are of particular concern as well as determining how many thermal cycles casings can go through before failure occurs. A nonlinear structural finite-element model of the cased section of high temperature geothermal well is presented and discussed here. The purpose of the model is to evaluate the structural integrity of casings when subjected to large temperature and pressure loads. The model can be used further to evaluate well designs and material selections for deep geothermal wells.