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

• Published in: Journal of Volcanology and Geothermal Research
• Main Authors: Friðleifsson, Guðmundur Ó., Elders, Wilfred, Zierenberg, Robert, Fowler, Andrew P.G., Weisenberger, Tobias, Mesfin, Kiflom, Sigurðsson, Ómar, Níelsson, Steinþór, Einarsson, Gunnlaugur, Óskarsson, Finnbogi, Guðnason, Egill Á., Tulinius, Helga, Hokstad, Ketil, Gibert, Benoit, Nono, Frank, Loggia, Didier, Parat, Fleurice, Cichy, Sarah, Escobedo, David, Mainprice, David
• Other Authors: Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA), Université de Pau et des Pays de l'Adour (UPPA), German Research Centre for Geosciences - Helmholtz-Centre Potsdam (GFZ)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: IDDP Reykjanes; Supercritical fluids; Deep drilling; Black smokers; Geothermal; [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; Mid-Atlantic Ridge; Reykjanes; Iceland
• Online Access: https://hal.umontpellier.fr/hal-02131788; https://doi.org/10.1016/j.jvolgeores.2018.08.013

International audience 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 ...