Deep Drilling: A Shared Infrastructure Across Multiple Energy Sectors
Deep drilling represents one of the largest investments in a geothermal project. According to a report from MIT and the U.S. Department of Energy, well construction could account for roughly 30% of the capital in certain projects with favorable resources, and climb to 60% or more when geological conditions were less advantageous [3].
This infrastructure isn't limited to geothermal energy, though. Exploring natural hydrogen, geological CO₂ storage, and recovering critical minerals all draw on similar skills, equipment, and services, even though each well must be designed for its specific purpose.
What Is Deep Drilling?
Deep drilling involves digging a well into the subsurface to reach a geological formation, resource, or reservoir located hundreds, or even thousands, of meters below the surface. It can be used to tap into the earth's heat, explore certain natural resources, or inject fluids into suitable formations.
There's no single depth at which a well is automatically considered "deep," though. The definition depends on the regulatory framework, the geological context, and the intended application.
Shallow Drilling versus Deep Drilling: Where Is the Line?
Under U.S. regulations governing certain offshore exploration activities, the Bureau of Ocean Energy Management defines a "deep stratigraphic test" as a well that penetrates more than 500 feet, or roughly 152 meters, below the seafloor [1]. This threshold reflects a specific regulatory context and isn't meant as a universal definition of deep drilling.
In the geothermal sector, the British Geological Survey places deep geothermal resources between 500 and 5,000 meters in depth [2]. This range reflects the diversity of geological settings and technologies involved. Geothermal projects long focused on high-temperature resources, above 160°C, that were accessible at less than 500 meters in certain favorable regions.
Advances in drilling techniques now make it possible to reach and use deeper resources, sometimes at more moderate temperatures. According to the BGS, fluids above roughly 60°C can supply heat to buildings, district heating networks, or industrial facilities [2].
For the purposes of this article, the term deep drilling mainly refers to wells exceeding 500 meters. The actual depths targeted vary considerably, however, depending on the sector, the temperature sought, and the characteristics of the subsurface.
Table 1 — Depth Thresholds by Context
| Context | Depth or Criterion Indicated |
|---|---|
| Deep stratigraphic test, U.S. offshore regulations | Penetration of more than 152 m below the seafloor |
| Deep geothermal resource per the BGS | 500 to 5,000 m |
| Enhanced geothermal systems, EGS | Wells reaching 2,000 to 5,000 m |
| Conventional geological CO₂ storage | Generally more than 800 m |
The Origins of Deep Drilling: Expertise Drawn from Multiple Industries
The technologies used in deep geothermal drilling largely stem from methods developed in the oil, gas, mining, and hydrogeology sectors. According to a report from MIT and the U.S. Department of Energy, the geothermal industry has adapted equipment, materials, and practices from these fields to suit its own needs [3].
Directional drilling is a notable example of this technology transfer. Unlike a strictly vertical well, this method allows the drilling path to be gradually adjusted to reach a precise underground target. Originally developed by the oil and gas industry, it's now used in numerous geothermal projects [3].
The European Commission's Joint Research Centre also notes that a large share of suppliers of subsurface equipment for geothermal projects come from the oil and gas supply chain. This includes drilling rigs, casing, pumps, and certain exploration equipment [4].
Deep drilling therefore rests on an already well-established industrial foundation. Applications differ from one sector to another, but many skills, tools, and services can be adapted for geothermal energy, natural hydrogen exploration, or geological CO₂ storage. That said, every project still requires a design tailored to its own goals, geological conditions, and well-integrity requirements.
Deep Drilling Serving Multiple Energy Sectors
Deep drilling plays a role in several sectors that draw on the resources and storage capacity of the subsurface. Geothermal energy, natural hydrogen, geological CO₂ storage, and critical mineral recovery each pursue different goals, yet they share some of the skills, equipment, and services needed to build wells.
This shared technological foundation doesn't mean a single well can automatically serve multiple purposes. Its design, materials, and operating method must be tailored to the geological conditions and intended use.
Natural Hydrogen: Exploring Underground Accumulations
Natural hydrogen, also known as geological hydrogen or white hydrogen, forms through various processes within the earth's crust, notably through reactions between water and certain iron-rich rocks. When it migrates and accumulates in a sufficiently sealed reservoir, it can become a resource potentially recoverable through drilling.
Exploring for it relies on several methods borrowed from the oil and gas industry, such as geological analysis, subsurface imaging, and the study of gases encountered while drilling.
Geothermal Energy, CO₂ Storage, and Critical Minerals
Deep drilling can also support several other energy and industrial applications:
Deep geothermal energy: enhanced geothermal systems, or EGS, aim to facilitate fluid circulation in deep, hot rocks whose natural permeability isn't sufficient. According to GEODEEP, some wells can reach 2,000 to 5,000 meters and target temperatures of 150 to 200°C [5]. Resources starting at around 60°C can also power buildings, industrial facilities, or heating networks [2] [4].
Geological CO₂ storage: drilling makes it possible to reach formations generally located more than 800 meters down, then inject CO₂ into them as a dense fluid [8]. Since it typically remains less dense than the reservoir's brine, the quality of the cap rock and the integrity of the well play a crucial role in its long-term containment.
Critical minerals: certain deep geothermal brines contain lithium and other critical materials of potential interest for recovery [4]. In this type of project, the extracted fluids can therefore supply heat while opening the door to a second economic activity. The viability of this recovery, however, depends on the brine's composition, the concentrations present, and the separation processes used.
Conclusion: One Body of Expertise, Many Possibilities
Deep drilling forms a shared technological foundation for several subsurface applications. Geothermal energy, natural hydrogen exploration, geological CO₂ storage, and critical mineral recovery all draw on comparable skills, equipment, and services, even though each project still requires a design suited to its own goals and geological setting.
Gaining better control over drilling costs, risks, and techniques could therefore support the growth of several sectors at once. This convergence doesn't make projects interchangeable, but it does encourage the sharing of know-how and the adaptation of already-established industrial capacity to new subsurface energy applications.
References
[1] "30 CFR § 551.1 - Definitions." Code of Federal Regulations, U.S. Government Publishing Office, rev. 2016, Bureau of Ocean Energy Management, https://www.law.cornell.edu/cfr/text/30/551.1.
[2] Jones, Darren, et al. "Unlocking the Deep Geothermal Energy Potential of the Carboniferous Limestone Supergroup." British Geological Survey, 28 June 2021, British Geological Survey, https://www.bgs.ac.uk/news/unlocking-the-deep-geothermal-energy-potential-of-the-carboniferous-limestone-supergroup/.
[3] Augustine, Chad, et al. "Drilling Technology and Costs." The Future of Geothermal Energy, MIT and U.S. Department of Energy, 2006, pp. 6-1–6-31, https://www1.eere.energy.gov/geothermal/pdfs/egs_chapter_6.pdf.
[4] Taylor, Nigel, et al. Clean Energy Technology Observatory: Deep Geothermal Heat and Power in the European Union – 2023 Status Report on Technology Development, Trends, Value Chains and Markets. Publications Office of the European Union, 2023, JRC135206, doi:10.2760/545601.
[5] "What Is Geothermal Energy." GEODEEP, 2020, GEODEEP Cluster, https://www.geodeep.fr/geodeep-cluster/what-is-geothermal-energy/.
[8] Parisio, Francesco, and Victor Vilarrasa. "Sinking CO₂ in Supercritical Reservoirs." Geophysical Research Letters, vol. 47, no. 23, 2020, e2020GL090456, doi:10.1029/2020GL090456.
