The Iceland Deep Drilling Project 4.5 km deep well, IDDP-2, in the seawater-recharged Reykjanes geothermal field in SW Iceland has successfully reached its supercritical target

Abstract

Abstract. The Iceland Deep Drilling Project research well RN-15/IDDP-2 at Reykjanes, Iceland, reached its target of supercritical conditions at a depth of 4.5 km in January 2017. After only 6 days of heating, the measured bottom hole temperature was 426 °C, and the fluid pressure was 34 MPa. The southern tip of the Reykjanes peninsula is the landward extension of the Mid-Atlantic Ridge in Iceland. Reykjanes is unique among Icelandic geothermal systems in that it is recharged by seawater, which has a critical point of 406 °C at 29.8 MPa. The geologic setting and fluid characteristics at Reykjanes provide a geochemical analog that allows us to investigate the roots of a mid-ocean ridge submarine black smoker hydrothermal system. Drilling began with deepening an existing 2.5 km deep vertical production well (RN-15) to 3 km depth, followed by inclined drilling directed towards the main upflow zone of the system, for a total slant depth of 4659 m ( ∼ 4.5 km vertical depth). Total circulation losses of drilling fluid were encountered below 2.5 km, which could not be cured using lost circulation blocking materials or multiple cement jobs. Accordingly, drilling continued to the total depth without return of drill cuttings. Thirteen spot coring attempts were made below 3 km depth. Rocks in the cores are basalts and dolerites with alteration ranging from upper greenschist facies to amphibolite facies, suggesting that formation temperatures at depth exceed 450 °C. High-permeability circulation-fluid loss zones (feed points or feed zones) were detected at multiple depth levels below 3 km depth to bottom. The largest circulation losses (most permeable zones) occurred between the bottom of the casing and 3.4 km depth. Permeable zones encountered below 3.4 km accepted less than 5 % of the injected water. Currently, the project is attempting soft stimulation to increase deep permeability. While it is too early to speculate on the energy potential of this well and its economics, the IDDP-2 is a milestone in the development of geothermal resources and the study of hydrothermal systems. It is the first well that successfully encountered supercritical hydrothermal conditions, with potential high-power output, and in which on-going hydrothermal metamorphism at amphibolite facies conditions can be observed. The next step will be to carry out flow testing and fluid sampling to determine the chemical and thermodynamic properties of the formation fluids.

Volatile Degassing From Magma Chambers as a Control on Volcanic Eruptions

“…Recent compilations of deep crustal permeability measurements (Achtziger‐Zupančič et al, ; Ingebritsen & Gleeson, ) clearly show that the permeability‐depth profiles of tectonically quiescent and active regions are markedly different with much larger permeability in active regions. Besides, in situ measurements of permeability in volcanic systems from drilling projects (Fridhleifsson et al, ; Ikeda et al, ; Reinsch et al, ) and lab experiments also suggest nonnegligible permeability even at temperatures higher than the brittle‐ductile transition (∼>500 °C; Watanabe, Numakura, et al ; Watanabe, Egawa, et al ).…”

New Conceptual Model for the Magma-Hydrothermal-Tectonic System of Krafla, NE Iceland

“…As mentioned above, no silicic rocks are found on the Reykjanes peninsula west of Hengill. The only occurrences are a basalt andesite intrusion encountered at a depth of around 800 m in well SG-12 in Svartsengi [60] and some felsite veins at the depth of 4634.5 m in IDDP-2 at the tip of the peninsula [61]. This is probably because the Reykjanes peninsula is a thin and young, basically oceanic, crust and different from crust further inland.…”

Tectonic and Anthropogenic Microseismic Activity While Drilling Toward Supercritical Conditions in the Larderello‐Travale Geothermal Field, Italy

“…Among these experiments, only the IDDP‐2 well in Reykjanes was able to provide a clear evidence of the occurrence of supercritical fluids. In January 2017 fluids at 426 °C and 34 MPa were reached at 4,500 m depth (Frileifsson et al, ) in Iceland. One of the most recent attempts to tap supercritical fluids took place in Italy at the Larderello‐Travale geothermal field (LTGF) in the framework of the DESCRAMBLE project (Bertani et al, ).…”