April 21, 2021

Team Profile:
Geological Controls on Geothermal Resources for Power Generation

Egbert Jolie & Isabelle Chambefort

photo credit:
Lloyd Homer

Isabelle Chambefort, Programme Leader for Geothermal: The Next Generation (GNG), has co-authored a recent paper:

Egbert Jolie, Samuel Scott, James Faulds, Isabelle Chambefort, Guðni Axelsson, Luis Carlos Gutiérrez-Negrín, Simona Regenspurg, Moritz Ziegler, Bridget Ayling, Alexander Richter & Meseret Teklemariam Zemedkun (2021) Geological controls on geothermal resources for power generation. Nature Reviews Earth & Environment.

The journal has made this article free-to-access for a couple of weeks – so download it while you can! And read on for a short interview with the lead author, Egbert Jolie, about the writing process for this review.  

Egbert Jolie and co-authors discuss the challenges that future geothermal development will likely face in their path to support sustainable green energy. They focus their discussion on the geological aspect controlling success in geothermal well targeting in intermediate to high-temperature geothermal systems. Geological setting and formations, permeability, fluids, and geothermal wells are amongst the subjects presented.

The following image (from the publication) shows how the enthalpy of geothermal fluids influences the potential of a geothermal reservoir for power production. Enthalpy is the energy per unit mass of a substance, and its value is determined by the temperature, pressure, and composition of the system where the substance occurs.

Thermodynamic availability (the maximum amount of electrical power that can be produced from reservoir fluids at a given pressure and temperature) increases with the vapour content of boiling fluids and temperature; “…supercritical temperatures reduce fluid viscosity and increase compressibility, resulting in higher fluid mobility and mass flow rates in production wells.”

Power generation potential - showing how the enthalpy of geothermal fluids influences the potential of a geothermal reservoir to produce power.

Egbert kindly agreed to answer a couple of questions regarding the “why” and “how” of this manuscript.

Egbert, why did you want to write this Nature Review?

When I was asked by the journal editors, if I would be interested to prepare a manuscript on this topic it took me only a few moments and I agreed. I was excited about the opportunity to develop this Review article, because all geothermal resources are controlled by the geology beneath our feet, and the success of a project depends on a thorough understanding of the heterogeneous subsurface.

The idea behind the article is the compilation of a comprehensive summary of our recent understanding and knowledge, and to provide further literature for anyone who is interested in the topic. The opportunity to communicate all this through Nature Reviews to many people, even outside the geothermal community, was very motivating.

Why was this the right time?

Nowadays, we are able to develop excellent reservoir models. At the same time, advanced computational methods for resource identification and characterization are getting more important. This provides outstanding opportunities for the geothermal market; however, we should always remember that the success of those technological innovations also depends on high-quality input data, and this is data on geology. Everyone involved in a geothermal project must be aware of this fact, including project developers, investors, funding agencies or insurance companies. A comprehensive Review on this topic, addressing a broad readership, didn’t exist before.

What are the key aspects you wanted to emphasize in this article?

The most important message of the article is to emphasize the importance of the key geological controls in geothermal systems. Without a reliable geological data base, we can still develop conceptual or numerical models, but a model is only as good as its input data and its value depends on a comprehensive understanding of the geology. Geological analyses require adequate financial resources and time. This is not only valid for geothermal energy, but also for any other activity related to georesources.

Furthermore, we still require advanced tools or platforms to integrate data from different scientific disciplines and different scales in a meaningful manner, which ultimately helps to better understand the key geological controls, also in unconventional geothermal resources. Such platforms will be important to find a common language and translate geological, geophysical and geochemical parameter into geothermal properties.

What did you learn that you didn’t expect (about this science and/or the process)?

Good question. For the preparation of the article, I’ve set-up a strong team of authors with broad experience in different disciplines and with different roles in the international geothermal community. It was surprising to realize how controversial issues can be discussed, even minor things like terminology. I’ve learned a lot through these discussions, and I’ve realized that such things are often simply related to different scientific backgrounds of people. In most cases there was no wrong or right, it’s more a matter of perspective. For that reason, we decided to add a glossary to the article and included careful definitions throughout the article.

Our research programme, Geothermal: The Next Generation, aims to improve scientific knowledge to de-risk exploration for Aotearoa’s supercritical geothermal development. In the manuscript you discuss supercritical resources as a future perspective. Why do you believe in the potential development of supercritical resources?

There is still a strong need to accelerate the development of geothermal energy projects, if the geothermal community wants to become more visible on the renewable energy market. This can be achieved by additional projects targeting conventional resources, but also relies on new technological concepts and unconventional approaches to harvest the geothermal energy at depth.

The potential of supercritical resources is enormous, and the geothermal market needs such innovations. Success in this field could be a game changer due to much higher power output and smaller surface footprints. It is very motivating to see that more international projects start focusing on this topic. We should also keep in mind that not all geothermal resources, which are technically exploitable should actually be targeted for power generation. Geothermal systems also deserve protection. From this perspective I think that supercritical resources will be a great addition once suitable utilization concepts, technologies and materials are available.

Dr. Egbert Jolie is a researcher at the German Research Centre for Geosciences GFZ in Potsdam and lecturer at FU Berlin. He was the scientific coordinator of the GEMex project (Cooperation in geothermal energy research Europe-Mexico for development of enhanced geothermal systems and superhot geothermal systems). His research interests include geothermal exploration and monitoring of intermediate to high enthalpy systems, magmatic volatiles, mapping and sampling in subaquatic environments, and supercritical geothermal systems. Egbert is co-founder of fluxtec, a Helmholtz Enterprise spin-off for innovative geothermal exploration and monitoring.

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