Materials for Geothermal Steam Utilization at Higher Temperatures and Pressure

Materials used in high temperature/pressure geothermal steam can be subjected to corrosion due to the aggressiveness of the geothermal fluid and non-condensable gasses such as hydrogen sulfide (H2S) and carbon dioxide (CO2), chloride ions (Cl - ) and hydrogen fluoride (HF). Icelandic Deep Drilling well (IDDP-1) in the Krafla area in NA Iceland gave well head temperature of 452°C at 140 bar pressure flowing 12 ks/s of superheated steam. This well alone could produce 25-35 MWe, but due to extreme conditions it is not currently operational. This paper focus on learnings from the material testing performed during the lifetime of the well and reveal several promising material choices for utilizing geothermal steam in extreme conditions like in IDDP1. Work is now ongoing in designing the next Icelandic Deep Drilling (IDDP-2) well in Iceland and expectations are to get 400-500°C steam with well head pressure over 100 bar. This will put several constrains on materials normally suitable for high temperature geothermal steam and calls for redesigning of materials, both down hole and above surface. Safety issues will be considered and direct or indirect use of the steam for electricity production will be discussed. Materials are evaluated based on research from the first IDDP well and possible changes in chemical composition of the geothermal fluid and gas contents are discussed.