The last posts were about batteries and pumped-hydro storage, which will be used to handle excess energy from variable renewables. But what happens when there’s no sun or wind for weeks on end? There still needs to be something to provide baseload power. Currently that’s done by nuclear and gas-powered plants, but nuclear is way expensive, and gas plants leak the powerful greenhouse gas methane, and emit CO2 as they burn. There are some other renewable resources still coming on-line, such as big hydro-power projects in northern Quebec, and some interesting work around tidal power plants, but more alternatives would be good.
Enter Eavor, who have a scheme for tapping the Earth’s heat in a much wider range of places than can be done at present:
They drill down to a hot layer, which may be kilometers under the surface, then take a right angle turn and go horizontally for a while. They put out multiple horizontal legs to maximize the surface area. Then they drill a second well next to the first, also with horizontal legs, and carefully connect them at the ends. Cold fluid sinks down the blue well, gets heated up, and rises up the red, where it can be used for process heat or to turn a generator.
The temperature out determines how well this works. Getting 200C is enough for some power, and for industrial heating applications and greenhouses. Getting 300C gets really efficient power generation, but usually means going a lot deeper. Well drilling is an O(N2 ) process, since the deeper you go the harder it is to turn the bit and to get the pipe in and out. That means that deep wells are far more expensive, so you better be sure you’re going to get really hot fluid back up.
The whole system is sealed, with no fluids going in or out of the rock. They use a proprietary casing called Rock-Pipe on the wells. This gets around a problem with geothermal at present, where tapping hot brine can cause the ground to shift in earthquakes, or perturb water levels. Having an open-loop system may not be as bad as the opponents of fracking claim, but a closed-loop scheme avoids the issue entirely.
They make a point of not using pumps to drive the fluid down, saying that that costs too much energy. They rely instead of “thermo-siphoning”, where fluid expands and rises as it heats up. They also don’t say what the fluid is, so maybe its thermal expansion factor is really high.
The key problem here is getting the wells to connect up when they’re kilometers underground. This is called Wellbore Intersection, and is apparently a standard service these days. They use something called Magnetic Ranging Technology, and one scheme for that looks like this:
After drilling one well, you put a sensor package down it that generates a magnetic field. A rotating magnet sensor in the second well can then pick up the first’s direction and distance, and guide the drill bit. You go as far as you can, and then guide the second well to connect with the first. It’s astonishing that this works.
Eavor has done one demo already in Alberta to test out the concept. They’re only aiming for 70C, but it’s just a demo. They’ve cut deals with firms in Bavaria and the Netherlands, and those should start soon. They recently raised $40M from BP and Chevron. That’s nice, but will only take them for one or two more wells. Their management team is mainly from Alberta, and look to be old hands at drilling. They’ve just brought an interesting guy onto their board, a Dutch professor of petroleum engineering from the University of Texas. He has been working on directional drilling for a long time.
All of this shows another advantage of this approach – it taps into the huge expertise and resources available in the oil & gas sector. There are lots of people who can do this once the tech is profitable. There are lots of oil companies that are looking at doom when (not if) fossil fuels are phased out, but could switch over to this and still have a future. There are lots of places like Texas and Alberta that are now striving mightily to hold back the renewables revolution, but could get their place at the table with this.
But it’s early days! It’s not clear in how many places this will work, or whether it’s economic. Everything gets cheaper as it’s scaled up, but first you have to show that it’s practical and reliable. Here’s wishing them luck!