The aim of the Iceland Deep Drilling Project (IDDP) is to 
drill a 4-5 km deep exploration well into a high-
temperature geothermal system in order to reach 400-
600°C hot supercritical hydrous fluid. The main purpose 
of the IDDP is to find out if it is economically feasible to 
extract energy and chemicals out of hydrothermal 
systems at supercritical conditions.
•	The IDDP design premises were initially 
assessed on basis of the presumed deep temperature 
and pressure values at the depth of 5,000 m. Two 
possibilities were considered, viz.:
Linear extrapolation from the established temperature 
and pressure values pertaining to the critical point in 
fresh water (374.15°C and 22.12 MPa)1, and 
considered to exist at a depth of 3,500 m. Linear 
extrapolation to 5,000 m depth yields a temperature of 
about 550°C and 25 MPa pressure.
•	Estimation based upon “Isochor” behaviour 
would on the other hand yield 391°C and 26.7 MPa at a 
depth of 5,000 m.
Three alternative temperature and pressure cases are 
selected for assessing load and stress conditions in the 
upper part of the anchor casing, the wellhead flange 
and the wellhead master valve.
Flowing well:
T= 500°C and P= 19,5 MPa (Linear)
T= 340°C and P= 14,5 MPa (Isochor)
Closed well:
T= 400°C and P= 22 Mpa
T= 20°C and P= 26.7 MPa
The casing design is based on the ASME Boiler and 
Pressure Vessel Code, Section VIII, Div 2, Alternative 
Rules.  Addenda July 1, 2003, and ANSI and API 
standards for flanges and valves. The design consisted 
of the following:
•	Design of anchor and production casings; 
ensuring strength integrity; materials and couplings 
selection.
•	Selection of materials and pressure class for 
wellhead master valve.
•	Selection materials and pressure class for 
wellhead master valve flanges.
The conclusion was to use thick K-55 grade steel for the 
casings, except for the top 300 m of the anchor casing 
where T-95 would  be used due to its creep resistance. 
The connections are Hydril 563 couplings and threads 
for the anchor and production casing, Wellhead and 
valves are to be of ANSI pressure Class 2500.

Grensasvegur 9
Reykjavik,
Iceland