READ MORE: Fossil fuel power stations could accelerate net zero – here’s how
Utah Forge (Frontier Observatory for Research in Geothermal Energy) is helping to make that happen. Managed by the Energy & Geoscience Institute at the University of Utah and sponsored by the US Department of Energy, the laboratory is developing and de-risking key technologies.
Principal investigator Dr Joseph Moore has managed the project for the last 10 years. With 50 years of industry expertise, he is also a research professor at the University of Utah. We spoke to him about the unusual conditions at the Utah Forge site, the risk of earthquakes from geothermal-related fracking, and the huge potential of EGS.
What makes the location of Utah Forge so suitable for geothermal research?
The Forge project is at depths where we commonly drill conventional geothermal systems. [With conventional systems] there's a source of heat, there's a source of permeability, there's fractures and there's water.
We can typically drill to 10,000 feet, a little over three kilometres. The Forge project is unusual in that respect because there's molten magma at relatively shallow depths, so we don't need to drill much deeper than 9-10,000 feet at this point to get temperatures of 225ºC. But typically, the temperature increases at 21-25ºC per kilometre.
Are the conditions accessible at the Utah Forge site potentially accessible around the world, at greater depths?
Correct. Our temperatures are higher than what you might normally find at those depths. That was one of the reasons Forge was selected.
The goal of Forge was to develop the tools and technologies for Enhanced Geothermal System development, and that meant de-risking tools and technologies, and drilling wells. Drilling wells is expensive, so the goal was to really limit the cost by drilling shallower.
How extreme are the conditions underground?
The Forge site is in granite. The site is, as I said, hot at relatively shallow depth with very little permeability – in fact, almost no permeability. So for EGS we need to create fractures, and that's one of the main challenges, to create the fractures that we need to allow water to circulate through the rock and extract heat from that rock.
People have been attempting to do EGS since the ‘70s, and really, there's no commercial project at this point. Maybe the closest would be Soultz in France or the one in Cornwall in the UK.
But these were actually hybrid systems. Forge has no permeability. Soultz, Cornwall, they had fractures – major fractures – and so there was some permeability in the rock. That's when we went from the concept of hot dry rock, no permeability, no fractures, to some fractures where we enhance the permeability, more like conventional geothermal systems.
Heat is challenging. This is a tool and technology development project. Anytime we get over say 200ºC, electronics tend to fail. It’s very difficult to make measurements at these temperatures, and measurements are critical for understanding what's going on.
It's very difficult to collect seismic data at reservoir depth – the seismic data is just a release of energy when the rock cracks. In order to understand where the fractures are going, how long they are, how they're evolving, we need to be able to measure it. Microseismic data is the best method for measuring it.
Drilling tools, especially those that work on electronics, are very difficult. The rock is very hard, and because it's hard, it's very abrasive. Think of a beautiful granite countertop – that's what we're dealing with.
We're trying to understand what is happening underground. An important reason for understanding fractures, for example, is we want to create a network of fractures that will allow us to extract heat over a long period of time. Typical geothermal wells, nowadays, maybe have a lifespan of 15 years. That’s what [the industry needs] to recoup the money we spent drilling the well. If there are short circuits, if we have too good a connection between the two wells, that is going to cool too quickly. We have to be able to understand what the connections look like.
That sounds like a lot of challenges. How is Utah Forge trying to solve them?
We were the first EGS project to drill a highly deviated well. Now that's important. Geothermal wells are typically vertical, or they’re slightly inclined, say 30º. It’s very, very easy to do. Oil and gas wells are horizontal, right? They go down vertically, then they turn horizontally. Our wells are 65º, not quite horizontal, but much, much more horizontal than a typical, near-vertical well.
Fractures tend to grow up, and so the more horizontal the well, the more fractures you can encounter. So that's just a very simple concept, but that's why oil and gas went that way as well.
We were the first to case wells. So usually the wells are left open-hole, and that has some challenges to it. If we case the well, if we put metal casing in the well, then we have much better control over flow devices. How do we control flow from different areas? How do we create the fractures?
Typically what we'll do is what the oil and gas industry does, they'll use what's called packers and plugs. We go into the well and we put a ‘cork’ down, called a plug, without a hole in it. Then we'll go in with a perforating gun, and we'll shoot holes in the casing. And those holes will go into the rock. They will be our fractures that allow us to get from the inside of the well to the rock. We then put water into the well, and we cause those holes to expand or cause fractures to form. That’s called fracking, basically, in the oil and gas industry and so that's what we do to stimulate the well because we have to create the fractures.
Once we've created the fractures, we go back in with the next plug and do it all over. It's called plug-and-perf, and we just do it all the way up the hole. Forge was the first project that did plug-and-perf in geothermal, so there were major issues in terms of ‘Will the elastomers that we're using for these plugs work?’ We had virtually 100% failure rate when we started, because it was too hot, over 200ºC. So we were the first to do that.
We were the first to stimulate rock behind casing. We were the first to measure seismic activity at reservoir depths, using new tools. We were the first to test new drilling technologies. One used BBs to fracture the rock and ideally drill faster, and the other used a mud hammer, more like a jackhammer. They weren't terribly successful, but we were the only group that was out there testing new tools and trying to build these tools.
Steam rises during circulation of water through wells at Utah Forge (Credit: Eric Larson, Flash Point SLC)
Fracking is a controversial topic, with concerns about earthquakes. What are the findings from the seismic testing you have carried out?
What happens in the oil and gas industry is that they produce water plus oil and or gas from the reservoir. The water that they produced cannot be put back into their reservoir, so that water has to go to some other site. In the US these are permanent injection sites. They're injection wells that are designed to take tens of millions of gallons of water and get rid of it, because you can't sell the water.
Eventually these injection sites fill up like a sponge. Any fractures that may exist in the subsurface, particularly in the basement rocks, can be lubricated. You have fractures, you reduce the stress, you lubricate the fault, and they slip – you get earthquakes where you never had any before. That's the problem with fracking.
EGS uses a different concept. The water that we inject into the well to make the system work is continually reinjected, so we don't take that water to some other site. Ideally we want 100% reinjection, 90% would be great.
We have gone in and done stimulations, and we've had hundreds of thousands of seismic events, but we haven't seen anything over two on the Richter scale. Up to two is an acceptable magnitude, you won't feel it at all, even if you're standing there. If you go then to say a three, you will feel it, activities have to stop. We've also developed a traffic light system, which defines our operations at different magnitudes.
How widespread could EGS become in future?
I think it has the potential to go anywhere. One of its real applications is going to conventional geothermal fields and drilling the margins. That’s a low-hanging fruit, because the margins are hot but they really lacked the permeability, and you’ve got all the infrastructure there.
You can use it for heating and cooling. You can use it for CO2 sequestration. I think there are any number of applications of EGS – ultra-hot, ultra-deep, where the energy density is maybe up to 10-times more than conventional geothermal.
Want the best engineering stories delivered straight to your inbox? The Professional Engineering newsletter gives you vital updates on the most cutting-edge engineering and exciting new job opportunities. To sign up, click here.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.