Heating up Europe's geothermal industry. Handling the downhole temperature with heat transfer and cooling solutions.

Across Europe, interest in geothermal projects has grown as officials search for ways to decarbonise their energy systems. At the end of 2022, the German government published a plan to increase the production of geothermal energy tenfold by 2030 to 10 terawatt hours (Twh). Across the border in France, the government has plans to increase the number of deep geothermal energy schemes by 40% by 2030. The Italian and numerous other European governments are also gearing up to support expansion.

This interest is unsurprising. According to the European Commission, with today’s technology, 25% of the European population can cost-effectively deploy geothermal heating and geothermal power plants could provide up to 10% of Europe’s power demand. Crucially, unlike other renewable energy sources, such as solar and wind, geothermal is constantly available.

So, the opportunity and appetite are clear. The challenge is achieving this in a commercially viable, efficient, and responsible manner. With higher CAPEX and lower initial returns compared to other energy projects, it’s vital to keep a tight leash on early-stage projects to avoid overruns – especially during the initial drilling stage.

Handling the heat

The thing about drilling geothermal wells is that, by definition, you are drilling in a high temperature environment. After all, heat is precisely what the project is all about. High temperature drilling is, of course, nothing new. The oil and gas sector has been drilling wells with bottomhole temperatures in excess of 149^oC for decades and has pioneered countless engineering innovations to better cope with such downhole conditions.

A crucial process in any high temperature drilling operation is mud cooling. The ambient heat downhole and friction-generated heat from drilling combine to heat the drilling fluids which must be cooled at the surface before being returned downhole. If the mud is not sufficiently cooled, not only can it emit fumes and vapours that pose a health and safety risk to the rig crew, but the temperature will continue to rise until it exceeds the temperature ratings for the equipment. At this point, measurement tools may be damaged or give false readings, or drill bits can fail.

Not only can this lead to expensive replacements for damaged equipment, but it incurs costly delays to the project. The drilling operator will typically have hired the rig, the rig crew, and the majority of the specialised equipment for the project. All of this comes with a day rate that quickly adds up, so anytime spent paying but not drilling, can seriously eat into an already squeezed margin.

Precise costs will vary project by project, but it’s likely that each day’s delay comes with a six-figure price tag. A typical geothermal well might take 90-180 days, so even a week or two of delays can significantly raise project costs.

Keeping their cool

Mud cooling is therefore critical to any commercially successful geothermal project. However, cooling itself comes with a cost, so it’s vital to correctly engineer a project-specific solution that balances the twin imperatives of mitigating risks and keeping a control on costs. One size does not fit all.

In offshore oil and gas drilling scenarios, the simplest approach to mud cooling is to use seawater as a cooling medium. For obvious reasons, this is not possible for geothermal projects, but a similar approach can be taken if the site happens to be adjacent to a suitable body of water, such as a river or water well. If so, while always safeguarding against contamination, the drilling operator may be able to meet all or a large portion of its cooling needs fairly cost-effectively.

The geothermal drilling dilemma

If the drilling site is not so obliging, then a more engineered approach must be taken. At one end of the spectrum, this could take the form of chillers. These are extremely effective and we have successfully used them for onshore drilling projects in the extreme heat of the Middle East. However, they are energy hungry and typically fuelled by diesel generators, so may compromise both cost and environmental, social and governance (ESG) considerations for a European geothermal project. More suitable alternatives might be dry air coolers or the use of cooling towers.

An intelligent approach must be taken on a site-by-site basis. For example, we have worked on a geothermal development in the upper Rhine Valley of Germany. Downhole temperatures were estimated at 155-190^oC with mud flowline temperatures of 80^oC, posing both surface health and safety and downhole tool integrity risks. In this instance, we designed a high volume mud cooler package with a hugely restricted cooling medium of one tank of water at only 25 per cent capacity. With a technician onsite to manage the equipment, we achieved a 25 per cent temperature reduction which safeguarded equipment integrity, the project schedule, and prevented surface-level health and safety risks to the crew.

Neo geothermal

A reminder: the European Commission says that with today’s technology, 25% of the European population can cost-effectively deploy geothermal heating and geothermal power plants could provide up to 10% of Europe’s power demand. That’s with today’s technology. No doubt tomorrow there will be advances that allow new approaches, that require us to drill deeper and tap into even higher temperatures. We’re already seeing a nascent generation of combined geothermal and lithium mining projects, which enjoy certain synergies that can improve project returns.

The one constant is change, and long experience in energy engineering teaches us that best practice is iterative and project-specific. Expert and attentive engineering for cooling methods will be indispensable for the rise of geothermal energy in Europe.