Unlocking underground energy storage with defunct fossil fuel infrastructure

Defunct fossil fuel infrastructure could play a key role in the energy transition when repurposed for underground energy storage (UES). 

A recent study out of Pennsylvania State University found that abandoned oil and gas wells (AOGWs) can be integrated into compressed-air energy storage systems (CAES) in order to take advantage of their natural geothermal heat. Rather than being environmental liabilities, AOGWs could serve as boons for energy storage. 

Researchers found that this combination can boost the efficiency of CAES by nearly 10%. 

Traditional CAES systems compress and store air underground during times of low energy demand and release that air to power turbines during peak loads. Compressing air heats it up and adds more pressure; expansion cools the air.  

Storing and using the heat generated from compressing can help improve the system’s efficiency and could potentially store more energy, which is why adding in geothermal heat from AOGWs can be such a valuable asset for CAES.  

Until now, these systems have struggled to reach commercial deployment due to tricky economics, but the improved efficiency could pave a smoother road to widespread rollout and make CAES projects more attractive to investors and utilities considering grid-scale storage.  

The report also notes that AOGWs offer some unique advantages like stability and natural insulation. And they’re easy to find: the U.S. Department of the Interior has documented 130,000 orphaned oil wells, with the U.S. Environmental Protection Agency estimating another two to three million AOGWs across the country. 

“These repurposing strategies not only address the challenges of renewable energy integration but also offer economic and environmental benefits by revitalizing abandoned sites and reducing the carbon footprint of energy production,” the study authors said, noting that these storage systems can easily tie into renewable energy generations. 

Retrofitting existing wells is much cheaper than drilling new underground energy storage facilities, which can be prohibitively expensive. Researchers also note that this approach can shave a year off of a project’s payback period and help lessen the sticker shock, as “the cash inflow in each year can reach over $10 million.” 

Repurposing AOGWs can also help provide job security and generate clean jobs in regions like Pennsylvania (where the study was conducted) that rely on the fossil fuel industry while also reducing potential environmental ramifications of unplugged wells.  

The study was published in the Journal of Energy Storage and was supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy; it was conducted through the Repurposing Center for Energy Transition at Penn State, which seeks to repurpose fossil energy infrastructure for energy transition applications.