Utilizing supercritical geothermal systems: a review of past ventures and ongoing research activities
Supercritical geothermal systems are very high-temperature geothermal systems that are located at depths near or below the brittle–ductile transition zone in the crust where the reservoir fluid is assumed to be in the supercritical state, that is for pure water, temperature and pressure are, respectively, in excess of 374 °C and 221 bar. These systems have garnered attention in recent years as a possible type of unconventional geothermal resource due to their very high enthalpy fluids. Supercritical conditions are often found at the roots of volcanic-hosted hydrothermal systems. More than 25 deep wells drilled in geothermal fields such as The Geysers, Salton Sea, and on Hawaii (USA), Kakkonda (Japan), Larderello (Italy), Krafla (Iceland), Los Humeros (Mexico), and Menengai (Kenya) have encountered temperatures in excess of 374 °C, and in some cases have encountered magma. Although fluid entries were documented for some of these wells, it remains an open question if permeability can be maintained at high enthalpy conditions. The IDDP-1 well at Krafla encountered magma, and ended up producing very high enthalpy fluids; however, these fluids were very corrosive and abrasive. Innovative drilling and well completion techniques are therefore needed to deal with the extreme temperatures and aggressive fluid chemistry compositions of these systems. New efforts are underway in Japan (northern Honshu), Italy (Larderello), Iceland (Reykjanes peninsula and Krafla), Mexico (Los Humeros), USA (Newberry), and New Zealand (Taupo Volcanic Zone) to investigate supercritical systems. Here, we review past studies, describe current research efforts, and outline the challenges and potential opportunities that these systems provide for international collaboration to ultimately utilize supercritical geothermal systems as a geothermal energy resource.
The Newberry Deep Drilling Project (NDDP) workshop
Abstract. The important scientific questions that will form the basis of a full
proposal to drill a deep well to the ductile–brittle transition zone
(T>400 ∘C) at Newberry Volcano, central Oregon
state, USA, were discussed during an International Continental Drilling
Program (ICDP) sponsored workshop held at the Oregon State
University-Cascades campus in Bend, Oregon, from 10 to 13 September 2017.
Newberry Volcano is one of the largest geothermal heat reservoirs in the USA
and has been extensively studied for the last 40 years. The Newberry Deep
Drilling Project (NDDP) will be located at an idle geothermal exploration
well, NWG 46-16, drilled in 2008, 3500 m deep and 340–374 ∘C at
bottom, which will be deepened another 1000 to 1300 m to reach
500 ∘C. The workshop concluded by setting ambitious goals for
the NDDP: (1) test the enhanced geothermal system (EGS) above the critical
point of water, (2) collect samples of rocks within the brittle–ductile
transition, (3) investigate volcanic hazards, (4) study magmatic
geomechanics, (5) calibrate geophysical imaging techniques, and (6) test
technology for drilling, well completion, and geophysical monitoring in a
very high-temperature environment. Based on these recommendations, a full
drilling proposal was submitted in January 2018 to the ICDP for deepening an
existing well. The next steps will be to continue building a team with
project, technology, and investment partners to make the NDDP a reality.

Geological evolution of the trachytic caldera volcano Menengai, Kenya Rift Valley
Menengai is a trachytic central volcano underlain by a high-level magma chamber. Activity started shortly before 0.18 Ma, with the growth of a low-angle trachyte lava shield having a volume of about 30 km³. Krakatau-style collapse to form a 77 km² caldera within an embayed ring-fracture was accompanied by the eruption of two ash-flow tuffs representing a combined magma volume of about 50 km³. The eruption of both tuffs was preceded by an air-fall phase. Both were emplaced as single flow units, and have intermediate aspect ratios of c. 1:4000. The tuffs cover an area of c.1350 km², including outcrops higher than the eruptive vents. During post-caldera times, some 25 km³ of magma was erupted, mostly as lava flows which now cover the caldera floor, but also as cinder cones and plinian-type tephra sheets. The chronology of syn- and post-caldera events is based on correlation with dated fluctuations in the levels of nearby lakes, suggesting that the two ash-flows may have been erupted at about 29 000 and before 12 850 years ago. Lake sediments inside the caldera provide evidence for a late intra-caldera lake from about 10 300 to 8300 years B.P.