Corrosion damage of injection string from the deep geothermal well IDDP-2 in Reykjanes Iceland

The second deep geothermal well drilled in the Iceland Deep Drilling Project (IDDP) at Reykjanes was completed in the year 2017. The final depth of the IDDP-2 well reached 4650 m depth, with a bottom hole temperature of 427°C and a pressure around 340 bar. The well was injected with cold tap water for stimulation after being completed. Temperature measurements were performed during an intermediate heat up in the well where no cold water injection was performed. A carbon steel injection pipe was implemented to the bottom of the well to ensure cold water and improved stimulation into the deepest part of the well. Extensive corrosion damages were discovered on the lowest part of the injection string when retrieved. Multiple axial cracks were also observed on the joint ends in a 600-meter interval of the pipe, from 4650 up to 4000 m depth. Failure analysis of damaged parts of the injection pipe with visual inspection and microscopic examination revealed extensive uniform and pitting corrosion. The analyze indicate that the high temperature and relatively high oxygen content in the cold water used for injection and contact with corrosive reservoir fluid caused the severe corrosion. The analysis of the cracks and hardness measurements of the joints indicate that sulfide stress corrosion cracking is the most likely cause of failure due to combined effect of thermal stresses, corrosive environment and susceptible material.