Geothermal: Turning Oil Wells Into Energy Storage
If you dig deep enough anywhere on Earth it gets hot not volcanic hot just steadily reliably hot for decades geothermal power has relied on finding rare places where the heat rises close to the surface like Iceland or parts of California if you didn't have the perfect geology you didn't have geothermal.
Cindy Taff, CEO of Sage Geosystems, spent 35 years at Shell building and drilling thousands of oil and gas wells her last job was driving down costs at scale and now she's applying those same skills to geothermal instead of searching for water and natural flow.
paths Sage drills for heat and then engineers the reservoir itself and then there is the twist along the way Sage realized the same underground systems could act like a battery storing energy under pressure and then releasing it on demand a bit like pumped hydro but underground no mountains required whether you can scale is still up for debate but this conversation is all about taking a century of subsurface expertise and repurposing it for an energy system that needs reliable carbon-free power around the clock.
The Shift from Conventional to Next-Generation Geothermal
Currently all of the production around the world is from conventional geothermal so when you think about conventional geothermal you think about Iceland or the geysers in California and what you're drilling for is a very unicorn or unique geology you're looking for water you're looking for heat of course and then you're looking for flow paths or permeability for that water to flow but because it's so unique it only represents about 2% of the geothermal potential around the world.
so next generation geothermal which is really looking for mainly heat and not water and permeability opens up that geothermal potential to probably 50 to 60% of the geothermal potential around the world.
The oil and gas industry drills just in the US 25 to 30,000 wells per year while the conventional geothermal industry may drill usually less than a hundred years and it's interesting because those industries never crossed paths before whereas now with next generation geothermal you're seeing a lot of that influence for the oil from the oil and gas industry coming into this hot dry rock or next generation geothermal resource for geothermal.
The skills the equipment the knowhow all of that is a really almost an exact overlay from oil and gas into geothermal and the other exciting thing is because the oil and gas industry is still operating it's really poised to help us scale next generation geothermal right now you don't have to build the skill sets you don't have to wait on all of that because it's ready to go right now.
Engineering the Reservoir
The earth's core is unbelievably high temperature and that heat radiates out toward the exterior of the earth and what we're tapping into for geothermal is that heat so you're drilling a well just like you do in oil and gas but for oil and gas of course you're looking for a specific layer of rock that contains either the oil or the gas what we're doing is drilling deep into the earth getting closer to that core where that heat is and so as we go deeper of course it gets it's it gets hotter.
What you're doing with next generation geothermal or this hot dry rock geothermal is you're drilling into the earth toward that heat and then you're also creating a or engineering a reservoir an artificial reservoir to simulate what mother nature is doing in conventional geothermal we do it through fractures we create a fracture in the earth and that gives you surface area to basically harvest the heat and then what you're doing is pumping water from the surface harvesting that heat and then using that water to carry the heat to the surface to generate electricity or you could use that heat for direct heating as well and so in the simplest forms geothermal is using the earth's heat as an energy source.
Solar and wind have done a great job draining the grid but they're intermittent wind produces power when the wind's blowing solar produces power when the sun is shining and so what geothermal gives you is a reliable dispatchable power 24/7 and it's carbon free.
Geothermal as Energy Storage: EarthStore
When we went in the field in 2021 in 2022 we re-entered a oil and gas well we created a fracture which is our artificial reservoir our engineered reservoir and we started operating that fracture to basically identify how best to get the heat out of the earth without putting a lot of energy into the system.
We noticed that we were having higher water losses than expected as well as friction losses or additional pressure that we had to overcome so we started operating that fracture instead of circulating through it we started operating it more like a balloon or you can use your lungs as an analogy we would put water into that fracture hold the fracture open with the water pressure just like your lungs are held open with the air pressure.
then we would basically open a valve at surface let that fracture close cuz mother nature's wanting to put that fracture back into the closed state and when we did we would get basically water to the surface under a great deal of pressure.
We recognized not only was this a way to reduce the amount of energy we're putting into a geothermal system but if we drilled a well shallower and we weren't even looking for heat we could turn that well into a energy storage system or a battery.
If you think about pump storage hydropower where you're pumping a lake up a mountain and then you're letting that lake basically rush down the mountain go through a Pelton turbine we're doing the same thing except we're doing it upside down so one of our reservoirs is deep in the earth and the advantage being that you don't need a mountain,
we actually have a higher energy density than most pump storage hydropowers because we're deeper than than the tallest pump storage hydropower so our battery is deep in the earth and it's using the water pressure and the earth's elasticity to store that water under pressure.
Technical Efficiency and Scalability
For a single well so say a well that has a 9 and 5/8 or 10 in casing we can get about a 3 megawatt capacity in the system and so what we're doing is we're we're cycling about 30,000 barrels of water in order to achieve the longer duration production we are targeting discharge durations of greater than 6 hours because we are not trying to compete with lithium-ion batteries they're doing a great job at the 2 to 4 hour discharge durations but for that 6 plus hours we're needing.
When we're ready to basically open that valve the water has to go about 4 ft in the piping to hit the Pelton turbine go through a nozzle hit the Pelton turbine we've tested that we can get that Pelton turbine spinning in less than 60 seconds. One thing that's an advantage with our technology that the lithium ion batteries don't have is when we cycle it we don't degrade it whereas when you're cycling lithium ion batteries the way I've heard it kind of phrased is you're kind of kind of beating up that battery so we're not having degradation because of cycling.
This next generation geothermal is tapping into a lot of the learnings from the oil and gas industry and in particular the unconventional shale revolution. During the unconventional shale development directional drilling drilling long laterals at a long at a low cost were really perfected as well as using hydraulic fracturing which you can use in next generation geothermal to create a very controlled engineered reservoir.
Pre-scale so under say 150 megawws you're looking at a cost of 10 to 12 cents a kilowatt hour if we can drive that scale up to 150 megawws or greater then we can get those costs below 10 cents a kilowatt hour.
Future Outlook and Energy Expansion
The DOE did a study and they compared the resource for conventional geothermal which was about 40 gawatt to the resource for next generation geothermal which is about 5.5 terowatt 5.5 terowatt is 5,500 gaww which is 5.5 million megawws and one megawatt in the US will power about 600 or 700 houses.
2026 2027 is going to be 4 to 8 megawws that's just for geothermal we'll have also storage at 10 to 15 megawws 2030 we're going to be probably in the 50 to 100 megawatt range.
Energy is the great equalizer everybody needs energy and everybody should have energy at a cost they can afford and so just being part of that journey is what excites me. We at Sage we're moving from building pilots to actually building at scale we've got our first commercial project at the Smecky coal plant we're going to be deploying our first commercial project with Meta we're working with ORAT and of course we're working with the Department of Defense.
We need more of an energy expansion than energy transition next generation geothermal is going to play a huge part of that and the oil and gas industry is really poised right now to scale that resource and tap into that resource
