World Geothermal Congress 2020+1
March - October, 2021

Magma-sourced Geothermal Energy and Plans for Krafla Magma Testbed

John EICHELBERGER, Charles CARRIGAN, Hjalti Pall INGOLFSSON, Yan LAVALLEE, John LUDDEN, Sigurdur MARKUSSON, Anette MORTENSEN, Paolo PAPALE, Freysteinn SIGMUNDSSON, Jefferson William TESTER, and The KMT Consortium

[, USA]

High-grade, high-temperature geothermal systems are needed for efficiently generating electricity. Often the heat source for these high-grade systems is believed to be associated with magma located below the producing reservoir, perhaps one kilometer deeper or more. Conventional geothermal resource analysis suggests that much of the intervening rock should be ductile and therefore impermeable. Beginning in 2005, geothermal drilling has accidentally intersected silica-rich magma at three very different sites (Hawaii, Iceland, and East African Rift) and at levels little or no deeper than earlier drilling. In all cases, best documented by Iceland Deep Drilling Project’s IDDP-1 in Landsvirkjun’s Krafla field, the transition from solid rock to near-liquidus magma is abrupt and evidence of magma crystallizing against its roof is absent. Because magma contains latent heat of crystallization, it has an order of magnitude higher energy density than equivalent crystalline rock. Latent heat of crystallization amounts to 10^18J/km^3 or 1 GWt if extracted continuously from 1 km^3 over 30 years. Moving heat through magma or rock (conduction) is slow, because both have low thermal conductivity. However, heat transport with flowing magma (advection) is much faster. If 10% of the latent heat of crystallization is delivered to a hydrothermal system by a magma convection current of r ~ 15 m rising at 1 cm/s, the heat transfer rate is about 1 GWt. Thus, in principle, modest convective flow in a magmatic source – consistent with absence of a thick crystallizing roof zone (mush) - can sustain a high geothermal power output if the energy is transferred to the hydrothermal system, where it can again be advected upward in aqueous fluid. However, the rate-controlling step is likely heat transport from magma to the hydrothermal system by conduction through a solid, but ductile, intact lid on the magma reservoir. If this distance is on the scale of meters, kept short by natural or induced thermal fracturing just above the lid as may be inferred for IDDP-1, then the characteristic thermal diffusion time will be years or less; but if hundreds of meters, then thousands of years. This means that producing hydrothermal fluid far from its heat source with a thick intervening conductive regime is effectively mining stored heat. Production proximal to magma taps fluid of far higher enthalpy (with more efficient conversion to electricity) taking energy directly from magma, potentially a much larger and self-renewing source. In one of the best characterized and monitored volcanic and hydrothermal systems in the world, IDDP-1 yielded a tantalizing glimpse of the coupling between hydrothermal and magmatic domains. There now exists an unprecedented opportunity to develop the first international magma observatory, Krafla Magma Testbed (KMT) to improve our quantitative understanding of coupled hydrothermal-magma systems. KMT will provide long-term infrastructure where science and engineering teams can conduct sampling, observations, and experiments in magma and its superhot rock envelope. Analogs from other science fields are particle accelerators and telescope arrays. Critical experiments in Phase One of KMT include: 1) coring through the rock-magma transition; 2) emplacement of a thermocouple string so that correlation of phase changes with temperature and direct calculation of heat flux from magma within the conductive lid can be made; 3) testing of novel slip-joints for casing that will make survival of superhot boreholes possible. As the project progresses, engineering tests of drilling materials, sensors, and energy extraction will be conducted. KMT will be the first deep laboratory in the last frontier of Earth’s crust, with the potential to revolutionize both geothermal energy and volcanology.

        Topic: Advanced Technology (Magma, Geopressure, etc.) Paper Number: 37027

         Session 42C: Advanced Technology 1 [Tuesday 6th July 2021, 10:00 am] (UTC-8)
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