| Title | Well Design and Drilling Plans of the Iceland Deep Drilling Project (IDDP) |
|---|---|
| Authors | Sverrir Thorhallsson, Bjarni Palsson, Sveinbjörn Hólmgeirsson, Kristinn Ingason, Matthías Matthíasson, Hinrik Árni Bóasson, Hannes Sverrisson |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | Iceland Deep Drilling, well design, supercritical steam |
| Abstract | The Iceland Deep Drilling Projects (IDDP) aim is to drill to 4-5 km to investigate the roots of geothermal systems. One question is whether it is technically and economically feasible to extract energy and chemicals where the temperature and pressure may be above the critical point which for fresh water is 374.15°C and 22.12 MPa. Such wells are planned to be drilled at three geothermal sites: Krafla (Landsvirkjun), Hellisheidi (Reykjavik Energy) and Reykjanes (HS Orka). Design and planning of the drilling project was given to the IDDP Drilling Technique Group. Several well designs and drilling scenarios were evaluated to meet the goals of the industrial sponsors and science funds. The scientist wanted to get as much core as possible during the drilling and the power companies for the well to be of large enough diameter for flow testing. Initial plans were for continuous coring below 2400 m with a hybrid coring system that would drill a 4 hole with a HQ wireline core barrel. The final decision was to abandon continuous coring and drill a wider hole and take only spot cores. The final section 3400-4500 m is a 8-1/2 hole where 10 m long 4 diameter spot cores will be taken. The IDDP well is deeper, wider and hotter than have been drilled to date in Iceland. By circulating large quantities of cold water during drilling it is hoped that the temperature inside the well can be maintained below 250°C allowing tri-cone bits to work and not require special materials. A modified core barrel was built to allow high water flows for improved cooling. Drilling mud will be used in drilling to 2400 m but water below that depth. Mud motors will be used to the same depth for improved rate of penetration. The wellhead has been designed for a maximum temperature of 500°C and pressure of 19.5 MPa. The well will have five cemented casing strings, all run from surface, 32 to 80 m, 24-1/2 to 300 m, 18-5/8 to 800 m, 13-5/8 and 13-3/8 to 2400 m and 9-5/8 to 3500 m. The open hole interval 3500-4500 m will have a 7 slotted liner. One of the main challenges is to successfully cement such long casing strings. Stage cementing was selected for the casings to 2400 m and 3500 m. Then the first stage is inner-string cementing to bottom and the second stage is by cementing through ports in the stage collar. Thick walled casing of API K-55 grade steel is selected, same steel as for conventional geothermal wells, except for the top 300 m of the anchor casing where API T-95 is used due to its creep resistance. The casing connections are Hydril/Tenaris 563 for the 13 5/8 and 13 3/8 anchor and 9 5/8 production casing. Wellhead and valves are of ANSI pressure Class 2500. The valves and expansion spool internal surfaces have weld overlays of stainless and hard facing to protect against eventual acid gases and erosion. The drilling cost of an IDDP well to 4500 m is estimated to be 20 million US$. Several papers at this conference describe the Krafla IDDP-1 well drilled in 2008-2009 which reached 2100 m instead of the target 4500 m as it intersected magma. |