| Title | Coring at Extreme Temperatures, Design and Operation of a Core barrel for the Iceland Deep Drilling Project (IDDP) |
|---|---|
| Authors | Alister Skinner, Paul Bowers, Sverrir Þórhallsson, Guðmundur Ómar Friðleifsson, Hermann Guðmundsson |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | core bit, bit cooling, coring, core tube data logger, high temperature core barrel, International Continental Drilling Project (ICDP), Iceland Deep Drilling Project (IDDP), Reykjanes Ridge, SW Iceland, RN-17, scientific coring, spot coring, supercritical |
| Abstract | The science program of the Iceland Deep Drilling Project (IDDP) requested that as much coring as possible should be done in the transition zone to supercritical and inside the supercritical zone (>374ºC), in the depth interval 2400-4500 m. Early ideas were to employ a hybrid mining-type wireline coring system and do continuous coring. This was abandoned in favour of taking spot cores (10 m in length) at selected depths in a production size hole of 8½” (215.9 mm). The coring system selected is of conventional design, non-wireline with a 7¼” (184.15 mm) OD and capable of collection of a 4” (101.6 mm) diameter core using an 8½” (215.9 mm) OD core bit. This system incorporates materials, clearances and bearings which are compatible with the operation of the core barrel at high temperatures. This is important as the projected temperatures in the IDDP scientific borehole before cooling could be as high as 450ºC. Special attention was given to the volume of flushing which could be applied to the core barrel and through the bit while running in/out and while coring and this in turn impacts on internal core barrel design of waterways and bearing configuration. Before the deployment in the IDDP it was decided to test the new core barrel and bit design. In November 2008 a very successful spot coring was performed at 2800 m depth in the production well RN-17 B at Reykjanes, where the formation temperature is 315ºC. Well RN-17B was being reconditioned by sidetracking it out of well RN-17 at 930 m depth below the production casing, to become an inclined exploration/production well. The core trial was performed in the open hole at 35º inclination. The main benefit of the core barrel is its unique feature to enable high water flow rates for cooling during coring, of up to 40 l/s. A core tube data logger was also designed and placed inside the inner barrel to monitor the effectiveness of cooling. The temperature could be maintained at 100ºC while coring but it reached 170ºC for a very short period while tripping in. The effective cooling is attributed to a top drive being employed which allows circulation while tripping in or out, except for the very short time when a new drill pipe connection is being made. A 9.3 m hydrothermally altered hyaloclastite breccia was cored with 100% core recovery, in spite of it being highly fractured. Unfortunately unexpected geological conditions in well IDDP-1 has precluded further use of the core barrel in this borehole and further operational results will have to await further developments in the IDDP program. |