Chloé Arson goes deep into the potential of geothermal heat

Chloé Arson, professor in the Department of Earth and Atmospheric Sciences in Cornell Engineering, discusses her interest in rock mechanics and geothermal heat, addresses common misunderstandings about the technology and recounts the unexpected, zigzagging journey that led to her becoming a literal rock star.

Transcript

David Nutt  00:05

Welcome to the Cornell Chronicle podcast, where we speak with the people behind our latest headlines about how they came to make their discoveries and what their discoveries mean for the world. Today we're talking with Chloe Arson, professor in the Department of Earth and Atmospheric Sciences, whose research interests center on damage and healing rock mechanics, micro, macro modeling of porous media and computational geomechanics. In short, Arson is a literal rock star. One of the major applications of this research is leveraging the role that geology plays in generating what's called earth source, or geothermal, heat.

David Nutt  00:44

Chloe, for the uninitiated, what is geothermal heat and how does your research address it?

Chloé Arson  00:50

So geothermal heat, as the name indicates, is heat coming from the earth. You have various ways to harvest it. Perhaps the most spectacular way to harvest it is to use geysers. The advantage of geysers is that it produces a heat carrier -- steam or water -- that is naturally ejected, so you don't even have to pump for it. Now there are many places where those geysers don't exist, and that led engineers and scientists to think about other ways to harvest this kind of heat. You have different kinds of technologies amenable to different depths. You've probably heard about shallow geothermal systems, which essentially consist in embedding coils at a few meters of depth. These are closed-loop systems where water or another fluid is circulated in a tubing system and gets heated as it passes through the soil. That is not the technology that I'm working on, which is more related to deep geothermal systems. So again, you have different ways to harvest heat at depth. The reason why we're interested in depth is that earth is hotter at depth. For example, in Ithaca, at three kilometers of depth, the region is at 80 Celsius degrees. So with that differential of temperature between the atmospheric temperature and the temperature of the rock, you may induce some energy using heat pumps, for instance. So here comes the research that we are working on. We are working on a system that would allow us to extract hot water circulated through a system of fractures within the rock in order to heat buildings. So what we are looking at is not a system that would produce electricity like you may have heard of in Utah or Nevada. The reason for this is at reasonable depth the rock is not hot enough. Other research groups are interested in those technologies where, essentially, you have two wells. One is used for pumping water underground, another one for extracting fluid out of the ground after it has circulated through the rock, and it is then used to activate turbines. That's not the technology we have in mind at Cornell, which is essentially inject a cold fluid in the rock, extract it after it passes through the hot rock at a higher temperature, pass it through a heat pump, and then circulate the heat carrier within buildings, in place of electrified heat systems. 

David Nutt  03:33

What are the components that you're studying to get there, like, what are some of the things that you're exploring?

Chloé Arson  03:38

So the part of the research that I'm specifically interested in is the prediction of fracture patterns. So in an ideal world, you would drill a vertical well and then deviate it laterally in a rock mass that's naturally hot, then drill another well next to it, inject water in the first well, push the water through the fractures collected from the second well, and the time that the fluid stays within the rock within the fractures would be sufficient to heat up that fluid as it comes to the second well. Of course, it doesn't work quite that way in natural systems. You don't have the natural fractures and the natural permeability that you normally would want to have in order to provide sufficient heating. And so usually, those systems have to be enhanced, enhanced means typically after drilling the wells, we need to induce fractures out of those wells in order to convey the fluid from one well to the next and allow those pathways between those wells. It is a complicated problem to design a fracture pattern, because the fracture that we induced, for example, by injecting a fluid at high pressure, interact with fractures that already exist.

Chloé Arson  05:00

Add to this that rocks are naturally very heterogeneous. They have a lot of defects, very tortuous, porous pathways, and so predicting those fracture patterns is difficult. So the work ahead is multifaceted. One is work with people who instrument reservoirs in order to collect data and somewhat back-calculate the properties of the rock in order to have an initial reference state of the reservoir model that we are using. The second one is to indeed model the reservoir with the data that we have. These data include geometry for geological information, hydrologic information, temperature distributions, rock properties, and then simulate processes, including the construction of the system, the drilling of the wells, the production of fractures, the operation of the system, the injection from a well, the collection from another well, playing around with different injection and pumping rates, different temperatures of injection, and see at what condition the reservoir will remain at a sufficient temperature. Can well imagine that if you keep pumping heat locally, the earth will become colder. Now the heat that is stored in those geological layers is so immense that it will naturally also regenerate, because the earth masses next to it are hot, and so temperature will come back to it. But in order to optimize the utilization of such a system, it is useful to alternate periods of usage and periods of rest, or alternate usage for heating and usage for cooling. When you heat you inject a cold fluid, you extract a hotter one. When you cool a building, you inject a hot fluid, you extract a cooler one, and that allows you to store heat back. So a lot of the work that we do in my group pertain to proposing a variety of models at different scales to understand the response of the rocks to those kind of stimulations. And that includes what we call forward modeling, where we have a process in mind that we can translate into an equation, then an equation that we can implement in a code. I typically use the finite-element method, which is a method that allows you to represent a reservoir into a variety of small elements of rocks and solve a system of equations at the scale of each element in order to have a representation of the entire evolution of the temperature, pore pressure and stresses in the rock, in the entire reservoir. That's one way to do it. Oftentimes the problems are very coupled. You have many degrees of freedom, including displacements, pressures, temperature, chemical concentrations, plus the possibility of propagating fractures. And when those problems become complicated, it is useful to develop surrogate models for portions of it, where you basically sequentially solve different portions of the problem and exchange information between different solvers after a few time-steps. And sometimes both solvers are forward models. Sometimes some of them are surrogate models. And those surrogate models we develop thanks to deep learning, so that is also part of the equation. Now, of course, I collaborate with many people. The entire field of geothermal energy encompasses more than just that. You can well imagine that people are also interested in induced seismicity, and there is a lot of research that pertain to that, on how to best instrument the site, how to read the data, how to combine different kinds of data in order to make sense of what's happening in the bedrock. I work with applied mathematicians who are very interested in the development of digital twins of reservoirs. So that's also an area for research. But don't forget the people interested in environmental laws. There are fundamental gaps in the laws that pertain energy, and there is really buoyant research in that area too, as well as techno-economic analysis and social impact

David Nutt  09:12

That's a lot. 

Chloé Arson  09:14

Yes.

David Nutt  09:15

What's the biggest misunderstanding about geothermal heat?

Chloé Arson  09:18

One is, okay, so one is, when you repurpose oil and gas equipment, does that mean that you deepen oil and gas wells and then inject something into a depleted oil well to then produce geothermal energy? No, that's not what we have in mind. You may have read some opinion pieces, including my own, calling for leveraging our knowledge of the oil and gas engineering field towards geothermal. But what we mean by that is that we can leverage the equipment, the type of drilling rigs and drill bits that we use, the kind of personnel who is typically deployed on site. To make boreholes deviate them laterally and produce fractures for geothermal reservoirs. But the thought is not to go back to oil and gas wells that have been depleted to work on them later on for geothermal purposes. So that's perhaps one of the misunderstandings. The other one is this idea of the risks associated with geothermal energy, because some of the techniques that are used in geothermal energy for deep technologies resemble the ones that we use for oil and gas. People often associate the same risks, for example, in geo seismicity, so induced seismicity in the oil and gas industry has been something that has been full of uncertainty, that has been causing a lot of turmoil, because there was a strong correlation between hydraulic fracturing events in shale reservoirs and induced seismicity close by, indeed in enhanced geothermal systems, systems for which it is necessary to engineer the reservoir to have sufficient permeability, for example, by creating fractures, hydraulic fracturing is the prevailing technology that is envisioned for a treatment of permeability. That being said, the type of rocks in which injections are made, the depth at which those injections are made and the volumes that are being injected are quite different, and so are the fluids that are being used. So the risks associated to seismicity are often related to the volumes being injected. When you think about an enhanced geothermal system, you hydraulic fracture the rock only once, when you produce a system of very conductive fractures to link several wells. Once those fractures are created, you inject and pump in a semi-closed loop. And you know, you you may have a little bit of loss of fluid along the way, because some of the fluids that are injected in the bedrock and pumped back may escape through fractures that are not connecting the wells and are connecting to the rest of the reservoir. But for the most part, it's a semi-closed loop system, and you're not injecting to produce fractures in operation mode. That's one thing. In the shale gas industry, you have to continuously produce hydraulic fractures if you want to continue to produce gas. So the risk of induced seismicity, we think, is higher. The technologies that have been developed to monitor seismicity have widely improved. There is, for example, at Cornell, a network of sensors that has already been deployed and has already measured the background seismicity, such that if a facility were to operate, we would be able to compare the level of seismicity during the construction of the facility and during its operation versus before. So that gives us an additional layer of protection, because we continuously would monitor the system, and we want to advance that area of research in terms of seismicity detection. So that's one of the main misunderstandings. Other associated risks that you may hear about geothermal as a translation or a proxy from the risks that people have heard about on from the shale gas industry include water usage. So as I explained, the system in EGS is a semi-closed loop you do use water that you cannot really reuse when you're in the phase of constructing the hydraulic fractures. Anything that you pump to produce the fractures would have to be extracted and then treated, usually for EGSes, you don't have treatment on site, so that means you wouldn't have wastewater plants just next to your operation, unless you do have a specific plant that is that has the capability of treating that water after you've used it for injection. So the risks of water pollution from disposal ponds is not comparable to the shale gas industry. After that, the use of water, again, is in semi-closed loop, so you may have a little bit of loss of water, but this is closely monitored and designed in such a way that you have minimum loss. Air pollution is not an excluded risk. When you drill through several layers, some layers may naturally contain natural gas that may escape throughout the well. This is also something that we learned how to monitor and keep track of. Some technologies are now being developed to precipitate the methane in place before it actually flares, before it actually escapes in the atmosphere. These also are mechanisms in place that have been continuously developed. So those risks are similar, but not comparable in magnitude to the risks that you would typically associate with the shale gas industry. So I would think these are the main misconceptions that people may have. Perhaps another thing that I could add is geothermal energy is really ubiquitous. If you do use it, not so much to produce electricity, but if you do use it for direct heat use, like what we're envisioning at Cornell, really you can, you can reach the temperature that you need at about three kilometers of depth, which is very achievable with the current state of the technologies for drilling. So there is a high potential to scale that technology at the scale of the entire country, if used properly, it can be renewable, as I explained before, you can avoid thermal drawdown, which is the depletion of heat in the reservoir, if you face the operations of a reservoir very wisely, in particular, if you use more than just one well pair, and you use different well pairs in sequence. So this is a very scalable energy. It is not a sparse system that only exist when geysers are here. So there's a high potential that may be also a misconception that often occurs, that people think that maybe it's only available at certain places in the country. It is potentially very scalable.

David Nutt  16:35

How did your interest in rocks and geothermal heat develop? I noticed on your your bio that you majored in philosophy as an undergrad. How do we get from philosophy to geothermal?

Chloé Arson  16:50

So I double majored. So that's why that happened. So the story was, when I was in high school, my favorite topics were mathematics and philosophy. And in France, you can't really study both at the same time. The system just doesn't work that way. You have to pick a track. So I picked the scientific track with the understanding that one day I would go back to philosophy somehow. I went into this very competitive program where you take two to three years of math and physics classes, you take a national exam, and depending on your ranking, you can enroll in one engineering school or the other. Was admitted in one of the top engineering schools in France that's traditionally very strong in civil engineering and mechanics. And as I entered my first year in engineering, I decided to go back to philosophy. So basically, I was pursuing two degrees at the same time from two different institutions. So I did that for one year. That was not sustainable to do that more than that. So during that year, I would go to the center of Paris reading books about epistemology and logics and the history of sciences and and then I would go back to the suburbs of Paris to study in my engineering degree. And along the way, I managed to get the first level degree in philosophy associated to epistemology, which I was really passionate about. And then when I entered in my second year of engineering school, I decided that I didn't have enough time to commute between the two institutions, but I still continued to read a lot of books of philosophy, history of science and sociology, but then I focused more on my engineering studies for my academic degrees, and so in the second year, you had to pick a major. I was more interested in math, but also was very intrigued by mechanics. I loved the mechanics how it's taught in France, because it's really applied applied mathematics in the way it's taught. And what I liked about it is this combination of mathematics and physics and the possibility of solving tangible problems from it. And so I picked a major that had the most mechanics in it, and in my school that was civil engineering, not even mechanical engineering. The civil engineering track had more mechanics courses than anything else. And so I picked that track. And along the way, I got more interested in geomechanics, which is the mechanics of soils, rocks and porous materials, because it had an environmental component to it. I could solve problems that were important for humanity because of their environmental impact. And my PhD thesis was on nuclear waste disposals, and the goal of the study was really to anticipate how much damage would be caused to the rock when you dispose of very hot waste in a rock that naturally contains fluids in it. So that was a very coupled problem involving mechanical processes, hydraulic processes, thermal processes and damage. So that's how I started with this idea of studying rocks damage and, later on, healing.

David Nutt  20:03

The range here. I mean, what? How do you feel about interdisciplinary work? It's something that we tout a lot of at Cornell, and I seem to constantly run into people that have this really crazy array of interests. I mean, do you put yourself in that category also?

Chloé Arson  20:19

Yes. So in several ways. The work that I do is at the intersection of science and engineering, and the bond between the two being mechanics. And in addition to that, at Cornell, I've been very active in trying to form a kind of collective of faculty members interested in deep geothermal energy, and that group is very interdisciplinary. We do have economists, philosophers, scientists, engineers and practitioners at the table. We also had environmental groups talk to us. So the idea being to cultivate an ecosystem of scholars interested in that topic, and when I started that group, I quickly realized that it was indispensable to have a continuous communication between all of these disciplines to make any progress. If one wanted to have an impact on society and an actual application to take place. Then little by little that led me to write proposals with a wider crowd of people. I have a proposal pending with somebody from the School of Public Policy. I have another one with an applied mathematician. So the anchor in all of that was geothermal energy, which is not only bearing a lot of scientific problems, but is also a societal issue, and that led me to form a more and more interdisciplinary group where, really it's several people working on problems together, developing proposals together, and hopefully, if it's funded, collaborating on projects, co-advising students. I also have this idea of developing a curriculum that would be of interest to engineers and potentially also of public policy students who might be interested in learning more about techno-economic analysis of renewable energies, for example. So all of those ideas have really been promoted by the Cornellian spirit of lowering the boundaries between different departments. It's been quite easy to reach out to people at Cornell and get them involved in workshops and discussions, to brainstorm on these ideas and propose something very unique that would completely integrate disciplines. So yes, I'm considering myself as an interdisciplinary researcher, but I also realize that it's work in progress. We can always do better. I could always take classes in public policy or get more training or more exposure. Time is limited, but I would say my gradient of interest leans towards more and more interdisciplinary work as I also strengthen my foundation in mechanics.

David Nutt  23:09

That's great. Okay, so this is a two parter. It's a bit of a, it might throw you. On the one hand, you know what has been your greatest professional achievement, you know, the thing that you're proudest of. But at the same time, what do you consider to be your biggest failure, you know? And what did you learn from each?

Chloé Arson  23:27

Yeah... So I think my biggest achievement has always been when I am able to make my students succeed. There is nothing more rewarding to me than this collaboration over the years with bright young scholars, and then seeing them taking off and taking ownership of their scientific projects, coming up with their own ideas to go further in the research that they've started in my group, and then seeing them succeed in their professional career, and I really enjoy keeping in touch with my former students, and soon former post docs, and seeing them becoming their own scientific selves. That has been the best part of my job. In terms of failures, there have been a lot of disappointments in my career. I've been unable to influence certain processes in academia the way I wanted them to improve. So the best failure, the worst failures, in my opinion, have been related more related to my inability to change certain rules, certain protocols, or perhaps the culture of the place in some instances, perhaps because of a clash of leadership style, perhaps because I tend to come up with a lot of ideas and solutions and bring a lot of energy, and people are not ready to really receive that quite yet. There are lots of reasons I question myself quite a bit in the process, but these are what I would consider my biggest failures. It's when I come in with, I see a lot of potential for a group of people to achieve a major milestone, or I see a lot of potential for a department to head in a certain way and lead in a certain area, and when I explain my vision for it and try to strategize with my colleagues that did not go anywhere for a variety of institutional blockages or perhaps some resistance to change as well. So these have been, I think, my main disappointments in my career.

David Nutt  25:49

And how do you deal with that? How do you cope with that, and how it is like in a way, how has that helped you, if it has or sharpened you, or given you a new vantage on things?

Chloé Arson  26:00

Yeah, so how do I handle that? So I cope with it by having an impact in other communities. For example, in my professional associations, I've been able to have an impact through mentoring of women in engineering. I've been elected to certain boards and committees, taking more leadership roles and trying to have an influence on the culture of the profession, taking on roles of as associate editors and organizing events, and trying to also inspire people in engaging in certain kinds of activities, like changing the way they educate on mechanics. For example, I had this interesting anecdote when I co-organized the Engineering Mechanics Institute conference at my prior institution at Georgia Tech, where two people to organize it, my colleague, Yang Wang and myself were the organizers. I was surprised that during the event, several women who were PhD students or post doc wanted a selfie with me because they had not seen many women organizing events in mechanics. So that pushed me to think that what I thought was just a normal thing to do could have more impact than I thought it could, and so I should really continue and double my energy reaching out and organizing events for professional development and impact. That's one way I've been coping. I've been, of course, nurturing a climate of mentoring and professional development in my own lab, which has always given me a lot of satisfaction, expanding my collaborations with other universities or other countries. But in some cases, I've left. In some cases, the culture was just not appropriate for me to stay, and I decided to just leave. That doesn't mean that I cut bridges with everybody, and in fact, it's interesting to see that maybe the waves that I made at the time I was very vocal about asking for change may actually have repercussion now that I'm no longer there, but sometimes that was the best course of action for me, because I discovered that I need a certain environment to be successful and happy.

David Nutt  28:20

How would you sort of characterize the trajectory of your research career? Has it been or has it felt like a straight line, a zigzag, a roller coaster, like when you sort of look at it over time? 

Chloé Arson  28:32

Yeah, it's not been a straight line for sure. Research is very non-linear in my experience. You have perhaps an inspiration or an idea, but at the time you have it, you have no funding, and sometimes you have the funding, but no student or post doc to help you achieve it, or vice versa. So a lot of times it's a very constrained way of achieving anything because of the way research operates. It's not like you're given constant flow of money and availability of people who can help you in your lab, and the output only depends on your inspiration. The inspiration is only one component of it in terms of your ability to deliver outputs that are visible, such as publications. So I've always been interested in the same kind of categories of problems, but the way I've been able to work on those problems have varied widely, depending on availability of funding and inspiration I could draw from the people working next to me. So I've always been interested in damage and healing mechanics in rocks, and looking at those processes from different scales. Also very interested in linking scales. For example, one of my favorite questions is, how can I make sense of the behavior of individual minerals when there are different kinds of minerals and cracks and pores all acting in synergy, and how can I predict the behavior of a composite that encompasses all of these different constituents interacting with one another? And this kind of center of interest has evolved over over the years as I gained more and more understanding of those levels of interactions and the type of interactions that are pertinent to look at for rock materials in particular. But the applications have changed. I was very focused on nuclear waste disposals during my PhD, but then when I joined the faculty at Texas A&M, Yucca Mountain shut down, and so I did not see a lot of future continuing in this kind of applications. At that time, I got interested in salt rock because the United States have been envisioning that salt rock could be a very good host material for nuclear waste, particularly military waste, because it has this ability to self-heal due to creep and pressure solution processes that I'm really happy to expand on but may not be relevant for this conversation. So that was a natural shift to adapt to the local environment I was in, while at the same time satisfying my desire to understand healing mechanics. And then as research evolved, I also got interested in other geological storage technologies. Soon in my career, people started talking about CO2 sequestration. That's a field that emerged as I was also evolving in the field. So I read more and more papers about storing different kinds of fluids underground, and then later on, on geothermal energy and hydraulic fracturing as it pertains to many applications in the energy sector, not only oil and gas, but also geothermal or geological hydrogen extraction. So yeah, this is how it evolved. And the same is true for numerical methods. The numerical methods I was taught as a grad students have diversified widely ever since I became a faculty member, and so the methods that I've employed to solve those research questions have evolved accordingly, leading to more research questions.

David Nutt  32:21

The combination of sort of, like scientific research on one hand and higher education on the other, you know, can can be all consuming. You know, how do you find some sort of, you know, work-life balance outside of the university?

Chloé Arson  32:33

Yeah, you'll often see that professors don't have a very clean, clear boundary between personal and work life, and I'm probably one of those. I love my job. I've wanted to be a professor since age 14. I already knew I wanted to do a PhD then, and for me, learning is fun. So there is a very thin boundary between work and personal life. There are certain constant things that I do, though when a little tired of either academic processes or teaching or intensive derivations of equations. I exercise. I love hiking. Ithaca is a great place to be in order to decompress being outdoors. So I enjoy that a lot. I watch Netflix. I enjoy a good glass of Finger Lakes wine with friends and good discussions. But do I have a clear boundary between work and personal life? No, my schedule is all over the place. When my brain is too tired for research, I take a break and I go for a walk and I go for a run, even if it's in the middle of the day, and then maybe I will work until midnight or 1 a.m., if that's required. I work during the weekend, but that doesn't mean I work all weekends, and that doesn't mean I don't take breaks, but my schedule is not is not in boxes, that's for sure, and sometimes it's a bad thing. I'm not really able to discipline myself say, well, I'm only going to work on this problem from nine to 10, and then I'm going to switch to that. I have a rough distribution of my effort for the week, but I never really stick to it precisely, and I let my mind wander around and then just deal with deadlines as they come, and sometimes work hard at the last minute. I try to avoid that, but sometimes it's inevitable.

David Nutt  34:29

When you look back on the trajectory of your research career so far, is there anything you would change?

Chloé Arson  34:37

It's hard to tell. My parents didn't necessarily have all the information that I have now in order to orient me in my curriculum. So if I had as a student all the information that I have now, maybe I would have chosen a slightly different study path, but I didn't know. So that was not an option. Also, my academic pursuits have changed over the years. My plan when I initially went into these very competitive prep classes and engineering schools that we call grande école for edited schools was to work for the French National Research Center, and life happened a bit differently. In order to have a position as a researcher in those centers, you need at least one or two postdocs. So at the end of my PhD, I was looking for a postdoc, preferably in an English speaking country, because those are more valued, usually on your CV than others. And at the same time, somebody advertised a position at Texas A&M, and I applied, and I got the job, and I had to choose between an academic job or a postdoc. And I thought to myself, well, at the end of the day, I want to be a professor, so why not try now? I didn't know anything about the requirements. I don't think I even really read my offer letter. I didn't know how many classes I was supposed to teach. I had never written a proposal, so it was really hard, and I really thought more than once that I would quit and go back to France and do something else. But there are certain aspects of the American academic system that I really enjoyed, particularly the education part, which I think is closer to the students than the system I was exposed to as a student. And so I decided to stay and make it work. And one thing leading to the next, I got married here. So now the map is quite different, so it's really hard to tell if I would change anything, because I consider myself happy. I'm happy with the life I've had. I've always wanted to have this dynamic interaction with lots of inspired researchers. I love my students, I love my colleagues here at Cornell, and I love Ithaca, so what's to change?

David Nutt  37:04

Okay, last question, what are you most excited about right now?

Chloé Arson  37:09

I'm the most excited by the resilience I see in people around me and their ability to transform challenges into opportunities. I think that's really what keeps me going, especially in challenging times when perhaps research is not supported the way we thought it could be. I'm also very excited by the way the university stands to its principles. That has been also a vector of motivation and perseverance on my end. Of course, I'm excited about the research that I'm working on, but that excitement towards the research that I'm working on, including geothermal, would not be there if I didn't have this institutional support and the excitement of the people around me.

David Nutt  37:58

I would agree with that. Thank you. I appreciate you talking with us today. 

Chloé Arson  38:02

Thank you.