CHAMPAIGN, Illinois – Researchers from the University of Illinois Urbana-Champaign have successfully demonstrated efficient geothermal heat storage while reusing a disused oil and gas well.
A new study led by Professor Tugce Baser of Civil and Environmental Engineering is the first field investigation of a geothermal energy storage system in the Illinois Basin — a geological structure deep underground.
The results are published in the journal Renewable Energy.
Baser said the Illinois Basin is a low-temperature basin, meaning it doesn’t naturally produce geothermal energy to generate electricity. However, the formations deeper underground have the thermal and hydraulic properties required to create an artificial geothermal reservoir.
“Many of the same properties that make a subterranean rock formation ideal for oil and gas production also make it ideal for geothermal storage,” Baser said. “And since our test site is a former gas well, it already has much of the necessary infrastructure in place.”
According to Baser, the pool contains spongy open-pore rock units and minerals with optimal thermal conductivity sandwiched between layers of insulation — providing the space and insulation needed to construct an artificial heat reservoir capable of holding liquids hot enough hold to generate electricity.
Using data from previous field observations and preliminary numerical modeling studies, the team chose to inject preheated fluid into the Cypress Sandstone, a porous rock unit located approximately 900 meters below the surface of the test site.
To test the site’s heat storage capacity, researchers injected water heated to 50 degrees Celsius into the well for three days in April 2021. After the well was shut down, the team monitored changes in pressure, thermal conditions, and hydraulics for five days.
“Our field results, combined with further numerical modelling, show that the process can maintain a thermal storage efficiency of 82%,” said Baser.
The study also reports an average total net cost of generating electricity of $0.138 per kilowatt hour, making the proposed system economically viable and viable.
“Our results show that the Illinois Basin can be an effective means of storing excess thermal energy from industrial sources and eventually from more sustainable sources like wind and solar,” Baser said. “The underground reservoir essentially functions as a large underground battery while reusing abandoned oil and gas wells. It’s a win-win situation.”
Researchers from the Illinois State Geological Survey and Projeo Corporation also contributed to this research.
The US Department of Energy supported this study.