Secrets of a Next-Gen Geothermal Company

Bastien Hermant – Lead Exploration Geologist

“Who knows how to swim through vast data sets?”

Episode 2 explores hydrothermal reservoirs vs. hydrothermal systems, flowing heat anomalies, the blind leading to brine and Angola’s underwater oil exploration as a conceptual model.

As we strive for a future powered by clean, abundant energy, TLS Tech Talks invites you to be a part of the conversation.

Dive deeper into the development, exploration, and production of geothermal energy with TLS.  Don’t miss out on this fascinating exploration. Subscribe, follow along and let us know what inside secrets you wanna know?

Thanks for listening!


Below you will find the complete transcript from Episode 2:

Rusty Muscarella: Hello and welcome to TLS Tech Talks Episode 2.1, today we are featuring Bastien Hermant, our Lead Exploration Geologist. Bastien, Thanks for joining us today, let’s start with you sharing a little bit about your experience in geology and where your inspiration came from to study it.

Bastien Hermant: Mmm, yeah. My first educational experience was at the engineering school in Nancy. Before that, I spent two years studying intensive mathematics and physics. Geology was relatively unknown to me then, aside from some high school teachings. 

During my time at the school, I chose to specialize in resource exploration and then geothermal energy. Geology, particularly high-temperature geothermal energy for electricity production, seemed like the best fit. 

I did an internship at TLS, seeking experience in high-temperature geothermal exploration. Since then, I’ve been working as an exploration geologist. Working alongside Mathieu Bellanger, a great geologist, has been incredibly educational. That’s why I’ve stayed for years, and I’m really happy to work here at TLS.

Rusty Muscarella: Beautiful. Next, can you tell us about geothermal systems compared to geothermal reservoirs?

Bastien Hermant: Yeah, it’s an important distinction. At TLS, we emphasize the difference between a geothermal reservoir and a geothermal system. The geothermal reservoir is the target, where you find hot water to produce electricity. In contrast, the geothermal system includes all aspects that produce the geothermal reservoir: where and how the heat anomaly induces hot water circulation.

Understanding the entire system is crucial because it helps determine the favorability of having a geothermal system and, therefore, a geothermal resource. We define a system as a combination of heat (the energy we’re looking for), fluid (the vector that transports this energy), and the drain or reservoir (where you find hot fluid circulation and storage).

You need all three components for a viable hydrothermal geothermal system. Other types of geothermal developments, like Enhanced Geothermal Systems (EGS) and Advanced Geothermal Systems (AGS), ignore some of these key elements. For instance, AGS focuses solely on heat, ignoring natural fluid and drainage/reservoir. Similarly, EGS focuses mainly on heat and attempts to build or improve the reservoir, then inject fluids.

However, with hydrothermal geothermal systems, which encompass most all current geothermal production, you need to consider all three key elements: heat, fluids, and the drain/reservoir. These are all very important.

Rusty Muscarella: Yep, nice. For TLS, tell us about TLS’s focus on identifying blind geothermal systems.

Bastien Hermant: Yeah, we think it’s important because several scientific publications in the western US show that most of the high geothermal potential is blind, meaning there are no surface manifestations like hot springs. For us, it’s obvious to focus on these blind systems because they represent most of the resource. It’s also quite challenging since you don’t have surface evidence, so you need to really understand how the system works. That’s why looking at geothermal systems is very interesting, because you know the key elements and what parameters influence these elements, allowing you to assess where you will find resources without relying on surface manifestations.

Not only surface manifestations but also data from previous exploration are important. Most resources, especially in the western US, were discovered thanks to hot springs or previous mineral and gas exploration. It’s really challenging to discover a truly blind system without anything on the surface.

Rusty Muscarella: Is this something that has been approached in the past but maybe the technology wasn’t available to identify, which is why there’s been a shift in focus?

Bastien Hermant: I think mainly because it’s easier to look for obvious resources. Potentially due to the lack of data in the past, but now with the number of projects, we have a lot of data, including regional data from geological surveys like the USGS and several universities producing strong datasets that help explore geothermal potential at a large scale. There’s a move in the geothermal community towards blind geothermal systems because we know they exist, they represent most of the resource, and we need to change the exploration parameters. 

At TLS, we’re working to discover these resources, much like the oil and gas industry did long ago. After finding obvious resources with oil seeps at the surface, the petroleum industry thought about the petroleum system and its key parameters to find resources, leading to huge discoveries offshore, like in Angola. There, you don’t have any oil seeps when looking at a resource beneath 2000 meters of water; it’s only based on the concept of the petroleum system. Similarly, in geothermal energy, we want to identify and understand the geothermal system’s key parameters to find resources based on a conceptual model.

Rusty Muscarella: So I guess this explains the unique process of TLS’ super top secret strategy to de-risk geothermal investments.

Bastien Hermant: The approach we use is quite new, and it’s founded on this exploration method. It leads us to focus on what we call the Crustal Fault Zone, a specific type of geothermal system that we believe is very ubiquitous. We can find it all over the world, and it has very high geothermal potential. It’s something we discovered in France, where we began our history at TLS. We have a project in the French Massif Central focused on Crustal Faults, but we also found this concept applicable in the US and many other countries. This led us to begin exploration in the US with new projects based on the Crustal Fault Zone system. 

We also developed artificial intelligence tools to help us manage and analyze the vast amounts of data we have, allowing us to rank which data are interesting and which parameters are crucial for assessing the system’s favorability. This has led to the development of machine learning and deep learning tools to evaluate geothermal potential and make the most of the data we have.

Rusty Muscarella: When you’re using this approach and technology, it’s data-heavy. Is data the only thing you integrate when choosing your prospects or locations?

Bastien Hermant: Obviously, there is still a geologist controlling the work done by our artificial intelligence software named DIG4GEO. The results of the favorability assessments are scientific, mainly based on geothermal potential. However, to develop geothermal power plants, we also consider other factors for economic viability. The first factor is the connection to the electric grid, which is crucial for project development. We map the electric grid and compare the results of geothermal favorability produced by DIG4GEO to create these maps, ensuring there is genuine economic geothermal potential.

Another important element is environmental stipulations. We want geothermal power plants to have the lowest possible impact on the environment. We carefully consider protected areas and regions with environmental stipulations because these can prolong project timelines and increase impact. By reducing environmental impact from the beginning, we make the project timeline more manageable. This conceptual approach to exploration helps us, especially in places like Nevada’s deserts, where hot springs indicate water and energy, leading to high biodiversity. Discovering blind geothermal systems far from hot springs allows us to develop viable power plants with minimal impact on local biodiversity.

Rusty Muscarella: How would you speak to the concept of abundance and the term durability, which we use as one of our parameters? Can you give us insights into how you calculate or understand the durability of hydrothermal systems?

Bastien Hermant: Yeah, there are several parameters to consider. First, we need to assess the volume of circulation we’re targeting, which involves understanding the cold water flow into the system. Next, we need to evaluate the amount of heat in the system since we’re extracting heat, not water, by pumping and reinjecting water into the ground. The main parameter is the heat, so we must model the heat entering and leaving the system. 

We do this through dynamic modeling, building geological models to simulate fluid circulation within the geothermal reservoir and fault zones. We can then experiment with different numbers of wells to see how they impact the resource in terms of temperature and fluid flow. The initial drilling and hydraulic tests from one or two wells, especially if we can connect them, will provide valuable data on the system’s dynamics. 

Conceptually, if the heat entering the system balances the heat we’re extracting, we can produce heat for a long time. However, geological systems can’t regenerate heat as quickly as we can extract it. The question is how long it will take before we see a decline in heat production. If the heat flow into the system is high, it could take hundreds of years to notice a decline. Conversely, if the system is small and we’re pumping too much, production and heat levels could decline rapidly.

Rusty Muscarella: I’ve heard of this occurring in other locations where durability was miscalculated. How do we monitor the flows and temperatures to track the impact on the heat source?

Bastien Hermant: Yes, monitoring fluid flow and temperature in each well is crucial. We also conduct tests between wells to determine how long it takes for water to travel from one well to another, which gives us information about the permeability and connection between wells. The model and production history will help us better assess the resource’s durability once we start producing. 

Rusty Muscarella: Yeah, I think like you said, there’s the science and the process at each stage of development to bring in the analysis and the proper tools to navigate efficiently and effectively the production of clean energy. In closing, can you share a bit about how you see the industry evolving and the scalability or real opportunities we are looking at with the success of our approach?

Bastien Hermant: I think we are at a key moment in geothermal exploration and for the geothermal community. People are increasingly aware that we need to produce more clean energy, and I’m sure that more and more people will become interested in geothermal energy because it has many advantages. Especially in the US, there is a lot of geothermal potential. So, I think the timing is great.

There are also efforts to develop other kinds of geothermal systems, like Enhanced Geothermal Systems (EGS) and Advanced Geothermal Systems (AGS). I’m looking forward to seeing what they will be able to produce, and it’s very interesting. However, I believe hydrothermal must remain the most interesting kind of geothermal energy because we know how to do it. When we discover something, we know how to produce clean energy from a viable geothermal system.

The key is our ability to discover the next blind geothermal system, and that’s where TLS excels. Our goal is to discover these systems through our conceptual approach and the technological tools we’ve developed to support this approach. I think this conceptual approach is highly scalable because once you understand the favorable parameters, you just need to find where these specific parameters exist elsewhere without relying on hot springs or other surface manifestations.

So, I think the timing is great for geothermal energy, and it’s also great for TLS to discover a lot of geothermal potential.

Rusty Muscarella: Beautiful. Yeah, I think we can continue digging into the approach that will allow us to identify these hidden sources. We also have a lot of technical processes to address, especially with our current projects in Nevada, with a major step being drilling. We’ll get to follow along as the process unfolds over the coming years and continue these conversations. If you have something else to share, we can continue, or we can say our goodbyes and share this conversation with the community interested in these clean energy opportunities and looking for solutions to some of our challenges.

Bastien Hermant: Just one thing I can share is that we are always open to sharing our knowledge and building strong collaborative relationships because the geothermal community is very small. We really need to help each other and bring geothermal energy to the place it belongs within the renewable energy landscape. For that, we need to build technological and financial partnerships to help each other develop projects. I believe there is enough space for everyone to develop their projects, including TLS and other companies. It’s important to keep in mind that we need to produce more clean energy to replace oil, gas, and coal plants. For that, we need to work together.

Sure, I think it’s part of my conviction to protect nature. I believe I am working towards that by having an impact on a global scale through producing clean energy at a more local scale. In France, particularly in the Pyrenees mountains close to Toulouse, it’s important to me. Sharing the real happiness of being in nature and witnessing its beauty is very important. It’s crucial to share this and teach people the importance of preserving nature.

Russ Muscarella: thank you listeners for tuning in, subscribing and commenting on our tech talks. Keep the questions coming and we will continue to share secrets from inside TLS. 

End of Transcript:


Ep 2.1
Ep 2.2

Episode 2.2 clip


“Insights from geothermal superheroes” Celebrating successes, reflecting on challenges, and uncovering massive opportunities in-between the crustal fault lines.

Geothermal Hydrothermal Exploration USA

Secrets of a Next-Gen Geothermal Company

Geothermal Exploration AI Tools
Mathieu Bellanger, Ph.D. 
20 Minute Listen /

“When drilling, we’re essentially asking detailed questions of the Earth”.

“While it’s possible we might encounter unexpected findings, our extensive preparatory work means that surprises are unlikely. If they occur, they would be outside the broad range of possibilities we’ve already considered.” 

You are tuned in to “TLS Tech Talks,” behind-the-scenes access to our AI-enhanced exploration tool development.

Thank you for being with us as we explore tales of perseverance, innovation, and the pursuit of truly sustainable energy solutions. 

Subscribe & stay tuned as we go deeper into the development of exploration, development, and production of geothermal energy.


Below you will find the abbreviated transcript from Episode 1.3: 

Rusty: Hey, welcome back to TLS Tech Talks with Mathieu Bellanger. This is the continuation of Episode 1, finishing our chat with Mathieu Bellanger. 
Mathieu: Our exploration strategy is all about probabilities and considering multiple models and scenarios. We gather extensive data across various scales, from lithospheric to fault interaction levels. When drilling, we’re essentially asking detailed questions of the Earth. While it’s possible we might encounter unexpected findings, our extensive preparatory work means that surprises are unlikely. If they occur, they would be outside the broad range of possibilities we’ve already considered.
Rusty: That’s a very methodical approach. Can you explain the role of algorithms in creating these geological models?
Mathieu: Our models are based on a combination of various factors like salinity, permeability, and thermal properties. These aren’t just single predictions but a range of possible scenarios that our data supports. The algorithms help us synthesize this information into coherent models that guide our exploration and drilling plans.
Rusty: Looking forward, once you’ve established a geothermal site, what’s the long-term impact on the target location?
Mathieu: Our simulations suggest that a geothermal site, especially in deep zones like those we target, can be exploited for over 30 years. We’re not just extracting heat; we’re engaging in a sustainable exchange with the Earth’s natural thermal systems. The size of these systems is incredibly vast, making long-term exploitation feasible.
Rusty: How do you quantify the energy potential of these geothermal systems?
Mathieu: We use a combination of mathematical and physical models to predict the energy potential. For example, in Buffalo Valley, we estimate a potential of around 50 MW of electrical power. This reflects the immense thermal energy present in the crust. However, it’s more meaningful to discuss how this energy translates into power plant capacity and what it means for human and societal needs.
Rusty: So, regarding the power capacity of the geothermal energy, you mentioned 50 MW. Could you elaborate on how this is calculated?
Mathieu: Certainly. When we talk about 50 MW, we refer to the installed capacity of a geothermal power plant, capable of operating at 70 to 90% efficiency. This means that if you install a 50 MW plant, it effectively produces 35-45 MW of power hour by hour, akin to a constant flow of energy.
Rusty: That’s quite efficient. How does this compare to other energy sources like solar?
Mathieu: Geothermal energy has a high availability factor. For instance, a 1-megawatt geothermal plant operates almost like a 0.9-megawatt plant continuously, unlike solar, where the actual energy yield might be lower due to various operational factors.
Rusty: Interesting. So, as TLS continues to evolve, do you see geothermal energy being used more in urban settings?
Mathieu: The potential for geothermal energy is vast, but its deployment depends on the geological properties of each location. It’s not always possible to find geothermal resources near cities. That’s why electricity, which can be easily transported, plays a crucial role in harnessing geothermal energy. For residential heating, for instance, the consistent temperature of the underground can be harnessed almost everywhere, but it still requires electricity to operate the systems.
Rusty: Does this mean geothermal energy is more suited to isolated locations rather than urban centers?
Mathieu: Geothermal resources are abundant, but they are not always situated near populated areas. We need to connect these resource-rich sites to consumers via power grids. California, for example, has great geothermal potential, but we must also consider seismic risks and ensure public safety.
Rusty: It seems like a balance between harnessing natural resources and ensuring community safety.
Mathieu: Absolutely. Our primary focus at TLS is to contribute positively to society. We aim to progress and improve life conditions, not regress. This commitment shapes our approach to every project we undertake.
Rusty: Perfect close. This talk has been very meaningful for me, and hopefully for our listeners. It gives us all an opportunity to share our voice and excitement about the projects

End Transcript – Please subscribe to TLS Tech Talks for Ep. 2 – Exploration Geology with Bastien Hermant

TLS Tech Talks Ep. 1.2

Secrets of a Next-Gen Geothermal Exploration Company

How do we identify the POROSITY & DURABILITY of a geothermal hydrothermal resource 6000 feet below the Earths surface?

You are tuned in to “TLS Tech Talks”, behind-the-scenes access to our AI-enhanced exploration tool development.

Part 2 of this episode we go deeper into the technical side of our geophysical tools. How is it possible to identify durability of a hydrothermal source? What do Legos and Python have in common?

Thank you for subscribing & traveling with us as we explore tales of perseverance, innovation, and the pursuit of truly sustainable energy solutions.

Subscribe & stay tuned as we go deeper into the development of Exploration, Development and Production of geothermal energy.


Below you will find the complete transcript from Episode 1.2 :

Rusty: Hey, welcome back to TLS Tech. Talks with Mathieu Bellanger. This is the continuation form episode 1.1… presenting geothermal clean energy exploration techniques.

Mathieu: High permeability allows for efficient fluid flow within the wells. The amount of heat you can extract depends not just on the temperature but also on the mass of fluid you can extract per unit of time. In highly permeable areas, you can extract significant quantities of fluid, which increases the amount of heat you can harness. But, you must manage the flow using pumps and maintain low pressure in the reservoir to avoid causing damage to the rock structure.

The injection index and production index are crucial parameters in this process. They link the pressure inside the system to the fluid flow rate achievable in the wells. For a system to be economical, you often need these indicators to be above certain levels. 

My work involves identifying such systems underground, even in the absence of surface manifestations like springs or volcanoes. The workflow we’ve developed at TLS is about exploring these systems and determining their economic viability. This approach is quite different from traditional methods used in the 2010s, which often relied on surface manifestations. We focus on crystalline rocks, a medium that wasn’t well-explored due to the lack of oil and gas resources. We’re looking to demonstrate the presence of geothermal resources in granite or crystalline rocks within fault zones through deep drilling projects in France.

Rusty: We’ve tried this approach in France and are working on it in the US, specifically in places like Buffalo Valley, you must be quite excited?

Mathieu: Absolutely, I’m very excited. The Basin and Range, from a geological perspective, is fascinating with significant mass transport and energy distribution. There’s a lot of energy potential at relatively shallow depths in Buffalo Valley. We have had to adapt our techniques slightly, considering it’s more sedimentary compared to our usual focus on crystalline rocks. We’ve adjusted our workflow accordingly.

Rusty: Could you elaborate on how you develop these 3D pictures of underground resources?

Mathieu: Certainly. In our exploration, we aim to create 3D images of the underground, which we do using various geophysical tools combined with geological knowledge. Although wells are expensive, we can still gather valuable data. We primarily use methods like gravimetry, ambient noise tomography, and seismic ambient noise recording. These methods help us record variations in electrical and magnetic fields over time, which are linked by an impedance tensor mostly dependent on the rock’s conductivity underground. 

By recording these variations, we can infer the underground’s electrical conductivity or resistivity. This approach gives us insight into the underground’s properties. However, interpreting these readings is challenging as multiple configurations can explain the data we record. We use joint inversion to combine petrophysical properties, reducing the number of possible models that explain our data.

Additionally, as a geologist, I’m interested in converting these physical properties into geological properties like lithology, temperature, porosity, and permeability. This conversion is crucial for understanding the potential for geothermal energy extraction.

Rusty: So, you’re developing tools that differ from traditional oil and gas exploration tools?

Mathieu: Yes, we’re exploring different environments than what’s typically sought in oil and gas exploration. Our tools are designed to identify hot underground locations suitable for geothermal energy. This approach differs significantly from traditional methods, which often miss potential geothermal sites. 

Most existing geothermal power plants are located near surface manifestations like springs, but our methods allow us to explore areas without such surface indicators. Jim Faulds’ work from Reno University shows that most geothermal systems are hidden with no surface manifestations. These systems account for a significant portion of geothermal resources. Our tools are tailored to identify these hidden systems, allowing us to explore geothermal energy in areas previously overlooked.

Rusty: So, your tools are specifically oriented towards the unique requirements of geothermal energy exploration?

Mathieu: Our tools are designed with the specific challenges and objectives of geothermal energy exploration in mind. We’ve developed them to adapt to different geological environments and to address the particular needs of identifying viable geothermal resources.

Rusty: We’re talking about geometries and underground properties. Could you explain more about the tools you use?

Mathieu: Absolutely, our work often revolves around understanding the geometry of faults and various underground properties. We’ve developed tools that help us manipulate spatial data, as geology is largely concerned with geometric problems. We’ve also been working on joint inversion methods, which I mentioned earlier, to convert physical properties into more geologically relevant information, like permeabilities and temperatures.

Rusty: So you’re using Python for programming these tools?

Mathieu: Yes, we use Python, a versatile scripting language, to develop our tools. It’s like having a vast array of bricks, similar to Legos, allowing us to build new things. We use Python for various tasks like data manipulation, visualization, cleaning, transforming, and even 3D modeling or simulations.

Rusty: That sounds like a comprehensive approach. Now, about Buffalo Valley, our most advanced project, what are the key aspects you focus on, especially concerning underground water sources?

Mathieu: In Buffalo Valley, and generally at depths greater than 1 kilometer, the water is quite different. In hydrothermal systems, the water is salt-rich, making it unsuitable for direct consumption. Our focus is on deep, hot waters, different from surface waters. To confirm the presence and qualities of these deep water sources, we look at various factors. For instance, in Buffalo Valley, we’ve identified water at depths between 1,500 to 2,000 meters, which likely originates from even deeper, around 6,000 meters. 

Rusty: How do you ensure sustainability and environmental safety in these operations?

Mathieu: We operate in closed systems, using both production and injection wells. The geothermal fluids are never exposed to the environment, ensuring no depletion of the underground resources. We focus on reinjecting the extracted fluids back into the ground after heat extraction, which is crucial for maintaining the system’s sustainability.

Rusty: So, understanding the sustainability aspect is key. How about the durability of the heat source?

Mathieu: In Buffalo Valley, there’s a high probability of magmatic systems contributing to the heat. However, it’s important to note that geothermal systems can be viable even without magmatic involvement. The heat can originate from the radioactivity of the crust or from deeper asthenospheric flows. These deep, hot materials, often related to plate subduction processes, are a significant heat source. This approach allows us to tap into geothermal energy in various geological settings, not limited to areas with magmatic activity.

Rusty: Let’s discuss the source of geothermal heat. How do you understand the dynamics of mass and energy transport within the crust?

Mathieu: The heat source for our geothermal projects comes from various deep-earth processes. For example, in areas like the Basin and Range, we have mass and energy transport due to geological activities over long periods. These processes facilitate the transport of heat vertically through the crust. It’s this heat that we aim to tap into and extract.

Rusty: It sounds like understanding the history and dynamics of an area is crucial. Could you elaborate on how you evaluate the potential of a geothermal site?

Mathieu: The longevity of thermal circulation is a key factor. For instance, whether the fluid  circulation has been ongoing for thousands or millions of years significantly impacts the potential of a site. In the Basin and Range, we’ve identified various periods of material and energy flows, making it an intriguing area for geothermal exploration.

Rusty: Thank you Mathieu. For those of you listening in, thank you for joining us, please subscribe and stay tuned for our 3rd segment with Mathieu Bellanger. 

End Transcript – See following Tech Talks Episode 1.3 for continued transcript.

Inside TLS Geothermics

Secrets of a Next-Gen Geothermal Exploration Company

Mathieu Bellanger – Head of R&D at TLS since 2014

Is there anywhere on Earth that hasn’t been touched by humans?

Tune in to “TLS Tech Talks” for behind-the-scenes access to our AI-enhanced exploration tool development. We dig thousands of feet below the surface of the Earth with big data geoscience.

Our first episode features a captivating conversation with our leading geoscientist, Mathieu Bellanger PhD sharing his journey and expertise in next-generation geothermal exploration.

From completing his PhD with a focus on field geology in the Western Alps to his pivotal role at TLS Geothermics, he shares the challenges and triumphs of securing geothermal licenses and beginning explorations.

By crafting advanced geophysical tools and innovative approaches like 3D imaging, Mathieu and his team aim to uncover hidden geothermal systems capable of sustaining long-term, economically viable, on-demand energy production. This conversation is not just about the technicalities of geothermal exploration but also about envisioning a future where clean energy is accessible and impactful.

Thank you for being with us as we explore tales of perseverance, innovation, and the pursuit of truly sustainable energy solutions.

If you enjoy this introduction, stay tuned for part 2 and 3 of this conversation.


For those who prefer to read, below you will find the complete transcript from our podcast:

Rusty: Hello and welcome to TLS Tech Talks Episode 1. This is Russ Muscarella and Im bringing you Mathieu Bellanger, he is Head of R&D at TLS and has been since 2014. Welcome Mathieu.

Mathieu: Hi, thanks for these meetings and the opportunity to discuss with you.

Rusty: Absolutely. Tell us a little bit about where you are and how you got there.

Mathieu: I’m in the southwest of France, close to Toulouse, living in the countryside because I enjoy being close to trees and nature. I work for TLS Geothermics, which is based in Toulouse. I’m an exploration geologist. Maybe I should start by talking about my journey before joining TLS.

Rusty: Sounds good.

Mathieu: Before my PhD, I studied geology at Orléans University, with a strong focus on field geology, geodynamics, and ore prospecting. Then, I completed my PhD at the same university, focusing on field geology in the Western Alps with a strong structural component. My research involved discussing processes during mountain building, extensive fieldwork, and laboratory measurements like chemistry and radiochronology to evaluate the timing of the deformation. After my PhD, I worked for a year as a teacher before becoming an exploration geologist in Geothermal energy. Interestingly, I hadn’t studied geothermal energy specifically before; I discovered it when I started working with TLS Geothermics.

Mathieu: In my first two years at TLS Geothermics, I wasn’t in Toulouse as we had no office. I worked from my home in the Western Alps, being the only employee at that time, starting in 2014. For more than three years, I was the sole employee, alongside the CEO of the company. During this time, our ambition was to obtain a geothermal license, which in France involves a slightly different process than in the US. In France, you must request an exploration license from the government to prioritize exploitation if you discover resources. You can conduct exploration without this license, but having it gives you priority over the resources in the targeted area.

Mathieu: At the start, we began our exploration quickly. I decided which area we would explore. Initially, we were looking for areas in France with potential geothermal resources. However, in 2014, there weren’t many in metropolitan France. One exception was a power plant in the Rhine Graben in the northeast of France, established several decades ago following oil and gas exploration that uncovered very hot areas. Initially, they intended to extract energy from dry rocks but discovered very hot rocks with significant fluid reserves, leading to the first power plant that utilized natural fluids within the fault zone, mostly below the basin.

Mathieu: At the start of my job at TLS Geothermics, everything was possible. We needed to build a workflow for our exploration, as our goal was to produce electrical power from geothermal energy in metropolitan areas. We focused on exploiting hydrothermal systems. Our intention was not to create overly complex systems or AGS, but rather hydrothermal systems, potentially with some enhancements or stimulation to connect the wells to the geothermal system, but with minimal intervention. We built our workflow to identify systems that could be extracted for economic value, aiming to be economically viable without external assistance. Initially, the feeding tariff for geothermal energy in France was favorable, allowing us to target fluids at 150°C at 5 kilometers depth. However, we aimed to track shallower resources based on the knowledge we had acquired, which suggested the possibility of finding such temperatures closer to 3 kilometers depth.

Rusty: So, this was your start. How did you build your workflow process?

Mathieu: Yes, we developed our workflow process using epistemology and complex thinking. This approach is crucial when you’re an explorer making world explorations. There are many unknowns, many things you don’t know. Therefore, it’s essential to manage this lack of knowledge to be able to identify the resources beneath the ground with very limited information. A significant aspect for us was to use epistemology, which allowed us to manage the knowledge we had and also acknowledge what we didn’t know.

We constructed a workflow to approach exploration, not in the traditional way. Typically, exploration starts from surface manifestations like active volcanoes, springs, or oil and gas wells. These are the classical starting points. However, we began with a conceptual model. From the beginning, we defined what combination of Earth’s properties we should meet to have geothermal resources. 

Rusty: Interesting. Can you elaborate on that?

Mathieu: Certainly, after defining our conceptual model, we tracked it in various areas. In our case, it was in the French Massif Central. This region is particularly intriguing because of the very shallow asthenosphere, a thin crust, which is rich in granite content and very radioactive. These conditions are ideal for brittle deformation, which is an essential factor for us.

Rusty: Did you say brittle transformation?

Mathieu: Yes, brittle deformation. It happens when you have strain. If the material is very hot, you can have a ductile strain where the deformation is distributed throughout the material. Conversely, in colder conditions, the deformation becomes more  brittle, localized along faults or failures, accommodating the strain. This distinction is crucial because brittle and ductile deformations have different properties for fluid flows.  Brittle deformation creates large spaces in various types of deformation, allowing fluids to flow through the crust with good velocity. However, near the  brittle-ductile transition or in the ductile part of the crust, the movement of water or fluids is different, with distinct properties and speeds, making resource exploitation more challenging.

Some people track these very hot areas for geothermal energy. But the main challenge, despite the high temperatures, is allowing fluid to flow and to extract the heat from the rocks. It’s very challenging to maintain the sufficient opening of the structures to allow fluid flows.

For us, the brittle part of the crust is the main target for hydrothermal systems, which we call permeability.

Rusty: So, permeability is essentially the ability of the medium to allow fluid flows, leading to more velocity and less pressure?

Mathieu: That’s right. Permeability is crucial because it dictates how easily the fluid can flow within the medium. Now, regarding how techniques have evolved in geothermal energy, there are several ways to extract heat. You can use totally impermeable mediums, which are very hot, and create artificial pathways for fluid flows to recover the heat from the rocks. However, maintaining permeability between wells has been challenging, leading to several failed attempts.

Rusty: Could you also talk a bit about EGS or Enhanced Geothermal Systems?

Mathieu: Certainly, EGS concerns stimulating the medium that already has strained mediums with lots of fractures and faults, and natural water. But you might find cementation in parts of these systems. To enhance the natural fluid flow, stimulation is applied, which can be chemical, thermal, or hydraulic, to increase permeability. But EGS is a bit confusing because it sits between the hot dry rock systems and hydrothermal systems. If an EGS system is close to a hydrothermal system, you don’t need to add much energy to increase permeability—it’s more about connecting the wells to natural systems. But EGS systems close to hot dry rock systems require significant energy to increase permeability.

Rusty: And what about the AGS approach?

Mathieu: AGS involves a closed loop, like a single well with both injection and production, or connecting two wells to circulate the water. Modern technology allows us to connect wells even at great depths. These systems can extract heat, but from our perspective and in terms of cost, they don’t seem the most economical way to extract heat from the earth. Our focus is on tracking cheaper ways to extract heat, primarily through hydrothermal systems.

Rusty: So why is it more economical to focus on hydrothermal systems?

Mathieu: Hydrothermal systems are more economical because they often consist of very permeable systems where the fluid flows naturally, creating thermal anomalies. There are three ways to transport heat: radiation, which is not very effective underground, conduction, which is heat transfer in solid mediums, and convection, where you transport mass and, with it, heat. Convection is an effective way to transport heat, especially when fluids naturally flow within the Earth.

Rusty: So, when fluids flow inside the Earth, they can transport heat, but convection can create thermal anomalies, which can be positive or negative. It’s essential in exploration to identify where there is upflow and downflow of fluids within the crust.

Mathieu: Exactly. Sometimes, an area might seem very cold, but if it’s an anomalously cold area, it might indicate convection. And close to this point, you could find very hot areas. It’s not just about finding heat; it’s about understanding the flow of fluids in the crust. In conduction, heat transfer is mostly homogeneous, depending on the thermal conductivity of the rocks. Some rocks, like clay or sedimentary rocks, don’t transfer heat well, but others, like granite, are excellent conductors.

In areas of convection, the situation is different. In places where fluid flows, the area is colder because of the influx of cooler fluids from the surface. These fluids then heat up and move towards the surface along specific pathways, creating hot zones. Fluid can flow for thousands, even millions of years, heating the surrounding rocks. It’s a misconception that you need magmatic activity to have geothermal resources. We’ve demonstrated that geothermal resources can be economically viable at temperatures between 150 to 250 degrees Celsius at depths of 3 to 4 kilometers, even without magmatic activity.

End Transcript – See following Tech Talks Episode 1.2 for continued transcript.

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geothermal specialists video interview

“Insights from geothermal superheroes”
Celebrating successes, reflecting on challenges, and uncovering massive opportunities in-between the crustal fault lines.

✨🌍The expansion of our Geothermal project portfolio with the launch of two new geothermal energy leases in Nevada!🌍✨