Yes, but drilling to 16-20 km represents a major engineering challenge that has not yet been demonstrated commercially with a conventional geothermal well. Conventional drilling technology has already reached exceptional depths: the Kola Superdeep Borehole reached approximately 12.3 km, while modern geothermal drilling continues to push the limits of depth and temperature. Fervo Energy, for example, drilled a geothermal well to 19,448 ft (5.93 km) measured depth, reaching a 460°F (~238°C) resource, demonstrating how rapidly modern oil-and-gas-derived drilling technology is advancing.

The Iceland Deep Drilling Project (IDDP) has demonstrated that conventional drilling technology can be used to access the SuperHot regime. IDDP's drilling strategy was based principally on conventional geothermal production-well technology, using large drilling rigs, rotary drilling, casing and cement, with specialised adaptations for the extreme conditions. At Reykjanes, IDDP-2 reached approximately 4.5 km and encountered supercritical conditions at temperatures above 400°C. The IDDP programme has also evaluated conventional drilling strategies targeting approximately 5 km and 500°C.

Why does it become so difficult? At extreme depths, several challenges increase simultaneously:

1. Temperature
Depending on the local geothermal gradient, temperatures approaching or exceeding 400-500°C may be encountered. Conventional downhole electronics, seals, drilling motors, measurement tools, elastomers, cement systems and other components have operating limits well below these temperatures. The US Department of Energy's current SUPERHOT programme specifically identifies the construction of wells capable of operating for 15 years or more above 375°C as a major technology-development challenge.

2. Pressure
Pressure increases enormously with depth. At 20 km, a simplified hydrostatic water column would already correspond to roughly 200 MPa (2,000 bar), while the weight of the overlying rock can produce lithostatic stresses on the order of 500 MPa (5,000 bar), depending on rock density and geological conditions. Actual formation pressure and stress will vary considerably by location.

These pressures place very high loads on casing, connections, wellheads, valves, cement, drilling equipment and pressure-control systems. Importantly, the pressure is not simply a load that the equipment has to withstand once: the well must remain mechanically stable while drilling, circulating fluids, running casing, cementing, completing and eventually producing.

3. Extreme mechanical loads and drilling dynamics
A 16-20 km drillstring is an extraordinarily long mechanical system. Weight, torque, bending, vibration, buckling, temperature-induced expansion and friction all become increasingly important. Bit wear and penetration rate become critical economic factors, while maintaining the required well trajectory becomes increasingly difficult.

Modern drilling technology is nevertheless progressing rapidly. Fervo's latest generation has demonstrated that deeper, hotter wells can be drilled substantially faster than only a few years ago: its Sawtooth 7 well reached 19,448 ft with a 7,500-ft lateral in 21 days. This is still only around 6 km measured depth, however, and should not be confused with demonstrating 16-20 km drilling.

4. Casing and cement
At extreme temperatures and pressures, the conventional steel-casing-and-Portland-cement system becomes increasingly difficult to maintain over the lifetime of a well. Thermal expansion and contraction can create substantial stresses, while cement integrity, casing connections and corrosion become critical issues. ARPA-E explicitly states that conventional steel casing/liner and Portland cement designs are inadequate for long-term superhot wells without significant modification or alternative approaches.

5. Supercritical-fluid chemistry
Supercritical geothermal fluids are not simply extremely hot water. Depending on the geological environment, they can contain dissolved salts, silica, CO₂, H₂S and other chemically aggressive constituents. As pressure, temperature and fluid chemistry change during circulation, minerals can precipitate and form scale while the fluid can attack casing, pipes, valves and heat-exchanger surfaces.

Conventional geothermal experience already demonstrates the seriousness of this problem: corrosion depends on factors including chloride concentration, pH, H₂S and temperature, while silica, metal sulphides and calcium carbonate are among the principal scaling mechanisms. Material selection therefore has to be based on the actual chemistry of the specific geothermal fluid rather than simply choosing a stronger grade of steel.

At SuperHot conditions, this challenge becomes significantly more severe. This is one reason why current research focuses not only on drilling, but also on new casing materials, coatings, cement systems, well architectures and high-temperature components.
 

How is Quaise different?
Quaise takes a fundamentally different approach to the deepest part of the well. Rather than attempting to extend conventional mechanical drilling all the way to 16-20 km, Quaise proposes to use conventional rotary drilling to reach basement rock and then switch to high-power millimeter-wave energy.

A surface-based gyrotron generates the millimeter waves, which are transmitted down the well through a waveguide. At the bottom of the well, the electromagnetic energy heats, melts and vaporizes the rock rather than mechanically crushing it with a conventional drill bit. A gas stream is then used to transport the resulting fine rock material back towards the surface.

This approach is designed specifically to overcome one of the fundamental limitations of conventional drilling: the deeper and hotter the well becomes, the more difficult it is to keep mechanical drilling equipment operating at the bottom of the hole.

Quaise therefore does not represent conventional drilling to 20 km. It represents a potential hybrid pathway: conventional drilling where conventional drilling works well, followed by a fundamentally different drilling technology where temperature and depth make conventional mechanical drilling increasingly difficult.

Quaise has now moved its millimeter-wave technology from laboratory development into field testing. In 2025 it reported reaching a 100-metre milestone in granite and subsequently reported further progress towards commercial-scale systems. This is an important technology-development milestone, but it is still a long way from demonstrating a 16-20 km production well.

What does this mean for Endoria?
Endoria's approach is deliberately based on the enormous body of knowledge accumulated by the oil & gas and geothermal industries using conventional drilling technology. IDDP demonstrates that conventional drilling can reach the SuperHot regime at favourable locations, while Fervo demonstrates how rapidly modern oil-and-gas-derived drilling technology is improving. Mazama is demonstrating SuperHot EGS at Newberry, where temperatures above 400°C occur at less than 5 km because of the exceptional local geothermal gradient.

Endoria's challenge is different: to extend these capabilities to locations where the required SuperHot temperature may occur substantially deeper below the surface.

We therefore do not regard 16-20 km as a single technological leap. It is a sequence of engineering challenges - drilling, well construction, materials, pressure control, high-temperature operation, fluid chemistry, heat transfer and power conversion - that must progressively be solved and validated.


Summarized:

Endoria sits at the intersection of two developments: the conventional deep-drilling capability is already there, the SuperHot geothermal resource has been demonstrated, and the remaining challenge is to make the combination work economically at the much greater depths that may be required in continental Europe.


The technology required to reach 16-20 km is not yet commercially proven. However, the underlying physics is well established, conventional drilling has already reached depths exceeding 12 km, modern geothermal drilling is rapidly moving towards deeper and hotter wells, and new technologies such as Quaise's millimeter-wave drilling are being developed specifically to overcome the limitations of conventional drilling.


Endoria's objective is therefore not to assume that today's technology can simply be extended to 20 km, but to combine proven deep-drilling technology with the next generation of high-temperature materials, drilling systems and engineering solutions required to make Ultra-Deep SuperHot Geothermal technically and economically viable.


Drilling costs generally increase substantially with depth, particularly as temperature, pressure, drilling time, and equipment requirements rise, resulting in exceptionally high initial CAPEX. However, because a geothermal plant requires no external feedstock - such as coal or natural gas - the ongoing fuel costs are zero. Over a long operational lifetime, this remarkably low OPEX offsets the steep upfront drilling expenses. While project economics remain site-specific, these factors ultimately make long-term project economics and revenue generation highly attractive. This topic is further outlined at FAQ-10.