Expanding a Geothermal Field Downwards. The Challenge of Drilling a Deep Well in the Hengill Area, SW Iceland.

Abstract

<p><span>In 1986 a well, which was planned as a convetional production well in the Nesjavellir Field in the Hengill Area, SW Iceland, was unexpectedly drilled into a very hot formation at the depth of 2.1 km. The measured temperature in the lowest part of the well was 380°C, which was the upper range of the measuring tool used. Thus, the bottom-hole temperature was most probably higher. No one expected to hit such a hot body in this place and the well design was not appropriate to handle such high temperatures and resulting pressures. Thus, the lower parts of that well were closed off and it has since then been operated as a conventional geothermal well.</span></p><p><span>This incidence sparked the idea of drilling deeper into volcanic hydrothermal systems in Iceland in order to gain a better understanding of the roots of the geothermal systems and to be able to produce fluids with higher enthalpy. The Iceland Deep Drilling Project (IDDP) is supposed to realize that idea. The IDDP project is a consortium of domestic and international partners, both from industry and academia. The three power companies in Iceland, which operate power-production in volcanic geothermal fields (Landsvirkjun, HS-Orka, OR), committed themselves to drill one deep well each in a field of theirs. </span></p><p><span>To date two wells have been drilled in the IDDP project. The first one, IDDP-1, was drilled in the Krafla Field, N Iceland, which is operated by Landsvirkjun, and the second well, IDDP-2, was drilled in the Reykjanes Field, which is operated by HS-Orka. The original plan was to drill down to 4-5 km. However, the IDDP-1 in Krafla was drilled into magma of rhyolite composition at the depth of 2.1 km and could therefore not be drilled further. During flow tests, it was flowing superheated steam at high pressure at well head temperature of 450°C. The power capacity was estimated to be 36 MW<sub>e</sub>. However, due to hostile chemistry of the fluid and damaged casing, the well had to be abandoned and closed after the well tests. IDDP-2 was drilled down to 4,659 m. The highest temperature measured in the bottom of the well was 426°C at a pressure of 340 bar. It was also possible to obtain core samples from the bottom of the well. However, due to damaged casing it hasn't been possible to do further temperature and pressure measurements in the lower parts of IDDP-2. To date flow tests in IDDP-2 have not started.</span></p><p><span>The next well in the IDDP project is planned in the Hengill Area. The most promising target is the hot body that started it all in the Nesjavellir Field. According to experience from IDDP-1 and IDDP-2 the main techincal obstacle is the casing. Both wells have serious casing problems. The magma body unexpectedly hit by IDDP-1 illustrated that careful interdisciplinary preperations are needed when drilling into the unknown. Currently, few projects are ongoing to fill the knowledge gaps in order to minimize risk and maximize the probability of successful drilling. </span></p>

Association Between Injection and Microseismicity in Geothermal Fields With Multiple Wells: Data‐Driven Modeling of Rotokawa, New Zealand, and Húsmúli, Iceland

“…Several seismicity spikes occur during this period, which are likely due to seismic swarms YU ET AL. 10.1029/2022JB025952 7 of 32 associated with injection activities, but could be a mix of natural and triggered seismicity (Gunnarsson et al, 2015;Juncu et al, 2020). While well HN-14 injects into low permeability hyaloclastite formation, HN-09 is injecting into a fairly permeable region, and HN-12 and HN-16 are drilled into a very permeable region (Gunnarsson, 2013).…”

“…10.1029/2022JB025952 7 of 32 associated with injection activities, but could be a mix of natural and triggered seismicity (Gunnarsson et al, 2015;Juncu et al, 2020). While well HN-14 injects into low permeability hyaloclastite formation, HN-09 is injecting into a fairly permeable region, and HN-12 and HN-16 are drilled into a very permeable region (Gunnarsson, 2013). Injectivity is dependent on the temperature of the injected water in all wells, which could be explained by a thermomechanical effect that promotes fracture opening in the fractured reservoir (Gunnarsson, 2011).…”

“…One reason for the sensitivity of these particular wells is that they are drilled into active faults, or are near to faults that are becoming reactivated by stress perturbations associated with injection. This could include stresses generated both from thermal cooling and stress transfer from other microseismicity events (Ágústsson et al, 2015;Gunnarsson, 2011Gunnarsson, , 2013.…”

“…HN14 lies on the Western-most part of the field and crosses paths with a NE-SW fault that seems to segment the reservoir and create a permeability boundary. This well has the lowest permeability of the five in Húsmúli (Gunnarsson, 2011), which might result in a larger pressure build-up (and hence higher or more responsive seismicity rate) compared with a higher permeability formation under the same injection rate/volume. Its sensitivity to microseismicity could be linked to spatially clustered events happening between 2016 and 2018 (Figure 3c), which could correspond to the periods of higher rate seismicity (Figure 7).…”

“…Annual reinjection at Húsmúli is about 12 million tonnes of geothermal brine and condensate (∼60°C–80°C) at depths between 1,200 and 2,100 m. Average rates into these wells have similar magnitudes over the study period (Figure 4), although there is considerable individual variability over short and medium time scales due to operational requirements. Several seismicity spikes occur during this period, which are likely due to seismic swarms associated with injection activities, but could be a mix of natural and triggered seismicity (Gunnarsson et al., 2015; Juncu et al., 2020). While well HN‐14 injects into low permeability hyaloclastite formation, HN‐09 is injecting into a fairly permeable region, and HN‐12 and HN‐16 are drilled into a very permeable region (Gunnarsson, 2013).…”