Proceedings World Geothermal Congress 2020+1 Reykjavik, Iceland, April - October 2021 1 Geological Risk Associated with Drilling into Magma at Krafla Caldera, Iceland: Preliminary Evaluation Olivera Ilic *1,3 , Freysteinn Sigmundsson 1 , Yan Lavallée 2 , Anette K. Mortensen 3 , John Eichelberger 4 , Sigurdur H. Markusson 3 , Paolo Papale 5 and Thor Thordarson 1 1 Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, 101 Reykjavík, Iceland 2 School of Environmental Sciences, University of Liverpool, Liverpool, UK 3 Landsvirkjun, Háaleitisbraut 68, 103 Reykjavík, Iceland 4 International Arctic Research Center (IARC), University of Alaska Fairbanks, Fairbanks, AK 99775-7340, USA 5 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, via Della Faggiola 32, 56126, Pisa, Italy * E-mail address: oli3@hi.is; oliverai@lv.is Keywords: Krafla, magma, drilling, KMT, Krafla Magma Testbed, risk, geological risk ABSTRACT Magma has been encountered unexpectedly when drilling in several volcanic regions in the world, one being in Iceland. In 2009, drilling of Iceland Deep Drilling Project’s IDDP-1, intended to reach supercritical conditions at a depth of 4 – 5 km beneath Krafla caldera, ended abruptly when ~900°C rhyolitic magma was intersected at a depth of 2.1 km. The aim of Krafla Magma Testbed (KMT) is to drill into shallow magma at Krafla to advance our understanding of magmatic systems and their coupling to hydrothermal reservoirs. It is unprecedented to purposefully drill into magma at these depths and this unusual objective raises the question of associated risks. Here we aim to identify and assess the geological risks and discuss mitigating measures. The active Krafla volcanic system, with its fissure swarm and caldera volcano had a volcano-tectonic episode in 1975-84 featuring nine eruptions. It is also a geothermal energy production site for the past 40 years. The current evaluation of risks is underpinned by existing geological, volcanological and geophysical knowledge of the Krafla volcanic system, experience from the IDDP-1 project, as well as experiences from drilling into magma in Menengai, Kenya and Puna, Hawaii. Identified risk factors include: i) upwelling of magma into the borehole and other movement of magma within the bedrock, ii) magmatic eruptions of rhyolitic or basaltic origin, iii) increase in seismic activity, iv) changes in the chemical composition of groundwater or hydrothermal fluid, and v) harmful gas emissions. There is also need for assessing how these factors could impact the ongoing energy production at the site. At both IDDP-1 and Puna, it is inferred that magma upwelled about 10 metres up into the borehole. Therefore, risk associated with magma upwelling is of particular concern and needs to be evaluated in detail. 1. INTRODUCTION Geothermal energy has been utilized since ancient times. In the beginning, geothermal water was used for bathing and washing. Later on, it was used for district heating and cooking as well and, since early last century, it has been used to produce electricity. Constant development within the sector has allowed geothermal power to become a viable option amongst renewable energy sources. In 2018, the world total installed capacity for geothermal power was 13,329 MWe according to data from the International Renewable Energy Agency (IRENA, 2018). However, this represents only ~0.6% of global energy production from renewable energy sources, and despite its advantages of small footprint and baseload power, adoption has lagged behind other clean, renewable energy resources. Increased worldwide demand for energy and the urgent need to reduce consumption of fossil fuels, calls for new ways to utilize geothermal energy so that sustainable production can be maintained. Recent advancements included the ability to drill deeper and to sustain high enthalpy wells at locations with a high thermal gradient. Ideas about drilling deep enough to reach supercritical conditions started surfacing around the turn of the century. One evolved into the Icelandic Deep Drilling Project, IDDP. The first of the project boreholes, IDDP-1, was drilled in Krafla caldera in 2009. The project came to a halt when the drill hit magma at 2100 m depth. IDDP- 1 was never completed in the sense that it never reached the designated depth and conditions. However, the well was maintained for the next two years and flow testing revealed that such a well might in fact support much higher production capacity than conventional geothermal wells (Elders et al., 2013). The IDDP-1 project generated new questions as to whether harnessing the energy of magma, the ultimate geothermal source, is possible. It also raised the possibility of directly observing and testing magma at depth for purposes of improving eruption hazard assessment and eruption forecasting. Hence arose a new initiative, the Krafla Magma Testbed, KMT. Although intentional magma drilling has never been undertaken, there are several instances of drilling encounters with magma. In 2005, during the drilling of injection well KS-13 at the Puna Geothermal Venture wellfield on the Big Island of Hawaii, a melt of dacitic composition was encountered at 2488 m depth (Teplow et al., 2009). In the fall of 2008, geothermal well KJ-39 was drilled to a depth of 2865 m in the Krafla geothermal field in north-eastern Iceland. The drill got stuck in the well and temperatures measured up to 385.6°C The drilling produced cuttings including silicic glass from the bottom of the well suggesting that the drill had intersected melt (Mortensen et al., 2010). In 2009 the IDDP-1 intersected magma and produced similar glassy cuttings. Two years later, in early 2011, drilling began for a geothermal well field in the Menengai volcano, Kenya. The plan was to drill to 3000 m depth but proximity to a magma body in the shallow crust prevented them from reaching the desired depth in some of the wells. Cuttings from two of the wells, MW-04 and MW-06, yielded glass at depths of ~2100 and ~2200 m respectively (Mbia et al., 2015). From a volcanology standpoint, the opportunity provided by retrieving glass directly quenched from magma at depth, provides us with a mean to constrain magmatic conditions, important for risk assessment.