Retrofitting abandoned oil wells into storage for renewable energy

Posted: October 20, 2025

Renewables promise clean, cheap energy. But when energy companies lack an adequate means of storing it, or can’t sell it to the grid, clean energy is often wasted—in Britain, energy companies are sometimes paid to stop producing when cables connected to the grid are overloaded. Energy bills stay high, and renewable megawatts are lost forever. 

Robust energy storage could help prevent this.

For short-term storage—five hours or less—lithium-ion batteries are cost-effective. Beyond that, stacking batteries becomes expensive and inefficient. To dispatch energy for longer durations, long-term storage is required, and an emerging geopressure storage battery developed by Sage Geosystems could fit the bill.

Batteries are not well-suited for extended periods of high energy demand, such as sustained consumption peaks, prolonged cloudy or windless weather, or grid emergencies. Because these events are rare or difficult to predict, utilities must invest in battery capacity that sits idle most of the time, driving up costs. In contrast, longer-term storage technologies, such as geopressured systems, can provide the same energy security at a lower overall cost.

Long-duration energy storage isn't new. Pumped hydropower, by far the most prevalent form of long-term storage, has been around since the early 20th century. It works by converting excess renewable electricity into gravitational potential and back into energy when needed. When more electricity is generated than is required to meet current demand, excess energy can be used to pump water from a low-elevation reservoir to a high-elevation reservoir. Then, when the grid needs energy, the water from the elevated reservoir is allowed to flow back to the lower one through Pelton Turbines, which are essentially water wheels that generate electricity when turned.

Pumped hydro is a proven and reliable technology. But there's a problem: It's a massive undertaking to deploy a new project, and it often requires specific geography—mountains and valleys. As more renewables are incorporated into the grid, finding alternatives to pumped hydro is indispensable in places where the landscape simply can't accommodate it.

Geopressure batteries could provide a solution suitable for nearly any geography.

Earthstore: pumped hydro turned upside down

The EarthStore battery, made by Sage Geosystems, depends on a network of underground fractures that expand and shrink like a pair of lungs, though they are filled with water rather than air. EarthStore absorbs excess energy from renewables by pumping water into the underground cracks, expanding and pressurizing them. To prevent the water from rushing to the surface, the fractures are plugged with a valve.

Then, when the sun goes down or the wind stops blowing, the water can be released; propelled by pressure, it shoots back up to the surface, turning turbines and generating electricity. “The Pelton turbine looks like a kid's pinwheel,” Cindy Taff, CEO of Sage Geosystems, told Our Industrial Life. “Basically, the water is spraying at a bucket on the wheel, and it makes the wheel turn. [It’s] very simple equipment, very low maintenance. And we're doing the same thing as pumped storage hydropower.”

And EarthStore doesn’t need mountains or valleys. It can be developed almost anywhere. The main geographical limitation for EarthStore is the subsurface, the layer of rock below the ground. If it’s too porous, Sage’s “earthen battery” wouldn’t work properly because the water would seep away and become depressurized.  

EarthStore also requires four to ten times less space than pumped hydro, while using significantly less water to deliver the same amount of energy. Sage achieves this by sending its fractures deep into the ground, where pressurized water holds the fractures open. At greater depths, the cracks are more resistant to opening, and more water pressure is required to hold them open. That means the deeper you go, the greater the storage potential. 

Gravity fracturing and geothermal energy 

In Sage's field validation of EarthStore, it used an abandoned oil well in South Texas, though the same process could be done anywhere by drilling a well from scratch. Sage deepened the existing well with gravity fracturing, a process that uses a high-density fluid, often weighted with minerals, to create fractures below the well. When the fracturing fluid fills up a well, its hydrostatic pressure increases in proportion to its height. A tall column of dense fluid exerts a tremendous downward force on the rock, which causes it to crack.

Sage has another technology that capitalizes on both mechanical energy storage and geothermal. In the right geologic conditions, and with deeper fractures, Sage breaks into hot subsurface rock—geothermal energy. Pumping water into this rock pressurizes and heats it up (increasing the pressure even further). 

When this heated water is released, the fracture will naturally try to close and propel the water to the surface as it does. The water that rushes back up the well bore is directed into pipes that carry it to turbines—and to heat exchangers if there’s significant geothermal energy. 

A mechanical storage system loses about 30 percent of the energy it stores. But with geothermal in the mix, Sage can improve its energy efficiency by generating power in addition to what is stored.  

To produce power 24/7, Sage imagines that two geothermal wells drilled in proximity would produce energy at different times. While one is pumped full of water, absorbing heat for about 12 hours, the other one is supplying heated, pressurized water that generates electricity. Then, they switch. The first well supplies water and heat for energy, and the other is pumped with new water. 

Sage'sfacility in Christine, Texas, is queued up for grid interconnection before the end of 2025, and the company recently announced a new partnership with a conventional geothermal company called Ormat Technologies. 

With Ormat, Sage will deploy its geothermal technology on a geothermal plant with untapped potential. Its gravity fracturing fluid will be used to drill below the conventional geothermal wellbore, giving Ormat access to new heat. Sage also has an agreement with Meta to build a geothermal plant east of the Rockies in 2027. This plant will primarily supply energy to a data center.

“As we build, we will continue to learn,” Taff says. “It's not anything different than what we did in the oil and gas industry.”