While other renewable energy sources, such as solar and wind, have grown significantly in recent years, geothermal energy has become an afterthought. This renewable energy was left behind. So, why do its most ardent supporters claim that the furnace beneath our feet has the potential to power the entire world? Despite decades of geological research, scientists know little about the planet’s interior movements. The typical image of the interior Earth — a globe with a wedge or hemisphere carved out to expose the four descending layers of crust, mantle, outer core, and inner core — hides a world of ambiguity.
The majority of what we claim to understand about this enigmatic world comes from laboratory simulations and seismic reflection surveys, which record the speed and amplitude of seismic waves travelling from the Earth’s core to various sites on the surface. The mantle is generally considered a semisolid layer of silicate rock, whereas the inner core is a massive ball of iron and nickel around 1,500 miles in circumference. Scientists have long hoped to reach the Mohorovičić Discontinuity, a theorised border between the crust and the seething mantle that may disclose more about our planet’s inner workings. However, no hole has been bored deep enough to collect a sample.
Regardless, or maybe because of ignorance, penetrating the underground has traditionally been associated with discovery and truth-seeking. Contemporary civilisation was built on the fossil fuels we ruthlessly took from underground seams and reservoirs, even though their burning on the surface now threatens our future. Down below, knowledge and devastation coexist. Treasure, like death, lies buried. The further you travel into the Earth’s interior, the hotter it becomes. Some of this heat is primordial, a byproduct of the Earth’s explosive formation. However, the vast majority of it is radiogenic. The interior of Earth is a crucible where unstable isotopes sizzle in an unstoppable radioactive decay.
Humanity’s excavations, as shallow as they are, indicate that crustal heat increases by an average of 100 degrees Fahrenheit each vertical mile. Temperatures in the hottest areas of the core are thought to be around 11,000 degrees, as hot as the sun’s surface. In other words, we live on the outside shell of a massive, functionally endless battery. Geothermal researchers say that harnessing just 0.1% of the Earth’s heat reserves will provide world energy demands for the next two million years.
Most current geothermal facilities are located in places with high tectonic activity, where superheated water may become trapped near the Earth’s surface, resulting in fumaroles, geysers, and hot springs. Atop the Mid-Atlantic Ridge, Iceland gets 30% of its power from these deep hydrothermal pools. The Geysers in Sonoma County, America’s first geothermal power complex, has been producing energy for Northern California since 1960 and is still the most prolific plant in the world. However, the overall capacity of such facilities is minimal globally. The maximum production from 198 geothermal fields in 32 nations is 16.3 gigawatts, less than 0.2% of overall power capacity and 1% of photovoltaic solar.
Various countries and international bodies are keen to increase geothermal output, and it remains a component of many decarbonisation roadmaps, not least because of its potential as a baseload “gap-filler” for more volatile renewable energy sources. At a Global Geothermal Alliance event in 2017, officials from 42 national governments signed the Florence Declaration, pledging to grow geothermal power capacity by 500% by 2030. As part of its Energy Earthshots initiative, the US Department of Energy said last year that it will “unlock” inexpensive geothermal energy for more than 65 million American homes by 2035.
In an age when politics frequently dominate energy policy, there is optimism that geothermal may also be politically neutral — the only renewable energy alternative that might please both climate change activists and “drill baby drill” advocates. “Environmentalists and drillers, dogs and cats, right and left: We all get what we want,” remarked technologist and climate activist Jamie C. Beard at a TED event in August 2021. “Clean energy where we need it, climate change solved, energy poverty eliminated, and drillers continue to drill.” In the next 30 years, we will solve energy if we form the correct partnerships and unify behind a common goal.”
The potential rewards are difficult to exaggerate. According to key research from the International Energy Agency (IEA), next-generation geothermal energy has “the technical potential to meet global electricity and heat demand many times over.” The investigation concluded that America’s national geothermal resource, based on an average well depth of slightly over 3 miles, is 7 terawatts, seven times the country’s present total energy capacity from all other sources combined. CATF estimates a fully established worldwide superhot rock sector could generate power for $25-30 per megawatt-hour, lower than the US market average. In the context of the climate problem, it appears to be a solution — hellfire recast as rescue. But the issue remains: how do we get there?
Industrial drilling remains a black art, although the fundamentals are the same as those of ancient rotary tools: When a sharp-tipped tool is put to a solid mass and spun, it creates downward pressure and bores a hole. On a mechanical deep-drilling rig, excavation is carried out by a heavy-duty bit, often a “tricone” assembly with three inward-canted rotating cones, each fitted with tungsten carbide teeth. A motor on the surface keeps the entire device rotating at around 50 rpm. As the drill’s weight and fluting move it lower, a steady flow of drilling fluid, or “mud” in industry jargon, is fed through perforations to cool and lubricate the cutting face and transport pulverised debris, or “cuttings,” back to the surface for disposal. This method has resulted in some astounding engineering marvels. A modern-day oil or gas well can reach 200 feet per hour. The world’s longest oil well is located in the UAE’s Upper Zakum oilfield, 50,000 feet beneath an artificial island off the coast of Abu Dhabi.
Russia holds the record for the deepest borehole, a “true vertical” hole bored perpendicular to the Earth’s surface. However, this one was excavated not for hydrocarbons but for scientific idealism and Cold War competitiveness. In 1970, a group of Soviet scientists and engineers started ground on what would become known as the Kola Superdeep Borehole. The location, located a hundred miles west of Murmansk in a tract of barren tundra near the Norwegian border, was chosen for its position atop the Baltic Shield, a massive slab of Precambrian metamorphic rock, where engineers expected the stable geology would control underground temperatures.
They built a roughly 250-foot-high derrick called the Uralmash-15000, a precisely engineered drilling platform weighing 15,000 tonnes, in the heart of a utilitarian complex of labs and barracks. Approximately 700 people worked shifts to keep the machine working day and night. Over two decades, they extracted over 10,000 cylindrical cores. Analysis of these rock samples revealed the existence of mineralised water deeper than ever before, as well as fossilised plankton up to four miles deep, which carbon-dating classified as Paleoproterozoic – remains of Earth’s oldest life. David Smythe, a Scottish geophysicist who visited in 1992 following perestroika, characterised the project as “the geological equivalent of going to the moon.”
However, it was also a lesson on the challenges of excavating bottomless trenches. Three kilometres down, the substrate began to exhibit surprising behaviour. The rock grew increasingly permeable, porous, and bendable as if the drill was passing through the plastic. The drilling angle had to be altered numerous times to stay on an actual vertical line, resulting in a pattern of abortive shafts that spread like a tree’s root system. As the rig crunched through layers of plutonic bedrock, the temperature increased significantly faster than the project’s experts had predicted. Downhole equipment began to deform at temperatures approaching 400 degrees; drill bits shattered on tougher rock. Pressure towards the bottom reached 150 megapascals, higher than in the deepest oceanic tunnels. Because of its exceptional depth, the Kola borehole covered just 0.2% of the Earth’s entire radius.
The sector must also address risks, both actual and imagined. Hydraulic fracturing for superdeep geothermal would not entail the harmful chemicals or fracture size used in shale gas production. However, the fracking issue stems from a reasonable public concern that we will never be entirely in control of underground forces, and it is not without merit. In 2017, water injection at an EGS trial project near Pohang, South Korea, caused a magnitude 5.5 earthquake. The shock wounded 90 individuals and inflicted an estimated $52 million in damage. One Korean seismologist called the incident “a wake-up call.”
Subsequent research revealed that a deep tectonic fault caused the quake that previous seismic profiling had failed to detect. In this perspective, the Kola scientists’ finding that subsurface rock becomes more ductile and less brittle at particular temperature and pressure circumstances might be a godsend. Industry experts are optimistic that EGS projects targeting deep parts of the crust, along with rigorous subsurface characterisation, will be able to reduce the danger of “induced seismicity.” Like so many others in the superhot geothermal realm, this subject demands more thorough inquiry.
A widespread belief among geothermal specialists is that marginal successes will ultimately approach critical mass, attracting more knowledge — and, more importantly, capital investment — away from oil and gas. However, other enthusiasts are also concerned that the techno-utopian fervour around superdeep geothermal risks overshadows more immediate benefits. Beard, the activist whose moving TED presentation on geothermal’s untapped potential has been seen over 2 million times, said that a universe of iteration between superhot rock and typical geothermal generation is being missed.
Author: Amar Chowdhury
