The Iceland Deep Drilling Project at Reykjanes: Drilling into the root zone of a black smoker analog

Guðmundur Friðleifsson, Wilfred A. Elders, Robert A. Zierenberg, Andrew P.G. Fowler, Tobias B. Weisenberger, Kiflom G. Mesfin, Ómar Sigurðsson, Steinþór Níelsson, Gunnlaugur Einarsson, Finnbogi Óskarsson, Egill Guðnason, Helga Tulinius, Ketil Hokstad, Gibert Benoit, Frank Nono, Didier Loggia, Fleurice Parat, Sarah B. Cichy, David Escobedo, David Mainprice

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Abstract

The aim of the Iceland Deep Drilling Project is to drill into supercritical geothermal systems and examine their economic potential. The exploratory well IDDP-2 was drilled in the Reykjanes geothermal field in SW Iceland, on the landward extension of the Mid-Atlantic Ridge. The Reykjanes geothermal field produces from a <300 °C reservoir at 1 to 2.5 km depth and is unusual because it is recharged by seawater. The well was cased to 3000 m depth, and then angled towards the main up-flow zone of the system, to a total slant depth of 4659 m (~4500 m vertical depth). Based on alteration mineral assemblages, joint inversion of wireline logging, and rate of heating measurements, the bottom hole temperature is estimated to be about 535 °C. The major problem encountered during drilling was the total loss of circulation below 3 km depth and continuing to the final depth. Drilling continued without recovering drill cuttings, consequently spot coring provided the only deep rock samples from the well. These cores are characteristic of a basaltic sheeted dike complex, with hydrothermal alteration mineral assemblages that range from greenschist to amphibolite facies, hornblende hornfels, and pyroxene hornfels, allowing the opportunity to investigate water-rock interaction in the active roots of an analog of a submarine hydrothermal system. As they have not yet been sampled, the composition of the deep fluids at Reykjanes is unknown at present. Cold water is currently being injected with the aim of enhancing permeability at depth, before allowing the well to heat up prior to flow tests planned for early 2019. The well has at least two fluid feed zones, a dominant one at 3.4 km depth and a second smaller one at 4.5 km. Extensive geophysical surveys of the Reykjanes Peninsula completed recently allow correlation of geophysical signals with rocks properties and in-situ conditions in the subsurface. Earthquake activity monitored with a local seismic network during drilling the IDDP-2 drilling detected abundant small earthquakes (ML ≤ 2) within the depth range of 3–5 km. A zone at 3–5 km depth below the producing geothermal field that was generally aseismic prior to drilling, but became seismically active during the drilling. The drilling of the IDDP-2 has achieved number of scientific and engineering firsts. It is the deepest and hottest drill hole so far sited on an active mid-ocean spreading center. It penetrated an active supercritical hydrothermal environment at depths analogous to those postulated as the high temperature reaction zones feeding black smoker systems.

Original languageEnglish (US)
Article number106435
JournalJournal of Volcanology and Geothermal Research
Volume391
DOIs
StatePublished - Feb 1 2020

Bibliographical note

Funding Information:
The IDDP-2 was funded by HS Orka , Landsvirkjun , Orkuveita Reykjavíkur , and the National Energy Authority (Orkustofnun) in Iceland , together with Statoil (Equinor) , the Norwegian Oil and Gas Company . The IDDP has also received funding from the EU H2020 (DEEPEGS, grant no. 690771 ). Funding for IDDP to obtain spot cores at Reykjanes and elsewhere was provided by ICDP and the US NSF (grant no. 05076725 ). EU FP7 project IMAGE (grant number No. 608553 ) supported petrophysical studies of cores. The authors also thank two anonymous reviewers for their contributions to the improvement of this paper.

Funding Information:
The IDDP-2 was funded by HS Orka, Landsvirkjun, Orkuveita Reykjavíkur, and the National Energy Authority (Orkustofnun) in Iceland, together with Statoil (Equinor), the Norwegian Oil and Gas Company. The IDDP has also received funding from the EU H2020 (DEEPEGS, grant no. 690771). Funding for IDDP to obtain spot cores at Reykjanes and elsewhere was provided by ICDP and the US NSF (grant no. 05076725). EU FP7 project IMAGE (grant number No. 608553) supported petrophysical studies of cores. The authors also thank two anonymous reviewers for their contributions to the improvement of this paper.

Publisher Copyright:
© 2018 Elsevier B.V.

Keywords

  • Black smokers
  • Deep drilling
  • Geothermal
  • IDDP
  • Reykjanes
  • Supercritical fluids

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