Geothermal Energy Storage From Abandoned Oil and Gas Wells
Researchers have discovered a way of repurposing methane-emitting oil and gas wells, transforming them into geothermal batteries for industrial waste heat.
Investigators from the University of Illinois Urbana-Champaign (UIUC) have successfully demonstrated a functioning geothermal battery system within the Illinois basin. This is the first field investigation using a geothermal energy storage system in an abandoned oil and gas well.
Abandoned oil well. Image used courtesy of Adobe Stock
The study was led by the UIUC’s Assistant Professor at the Department of Civil and Environmental Engineering, Tugce Baser. Other contributing researchers included those from the Projeo Corporation and the Illinois State Geological Survey. The study findings were published in the journal Renewable Energy.
According to a policy analysis published in the Environmental Science and Technology journal, millions of abandoned oil and gas wells are peppered across the U.S.
Since the excavation and drilling of these wells in the 1800s, many have been left unplugged and unused.
The U.S. Environmental Protection Agency estimates around 3.2 million abandoned wells are not being used for injection, production, or other activities. Of these 3.2 million wells, about 2.1 million are believed to be unplugged abandoned wells.
In the early days of the oil and gas industry, regulatory programs did not provide incentives for well decommissioning, nor did they map drilled wells' locations. With this in mind, the estimated abandoned wells mentioned above cannot be taken at face value.
A schematic depicting the type of geothermal battery used in the research study. Image used courtesy of Tugce Baser and Renewable Energy
Environmental Costs, Decommissioning Abandoned Wells
Abandoned, unplugged oil and gas wells can leak methane into the atmosphere, leading to serious environmental implications. The structural integrity of wells can diminish over time and cause gas and fluid to leak into groundwater or surface water. In addition to water contamination, other harmful air pollutants (benzene, hydrogen sulfide, volatile organic compounds, or benzene) can be released from unplugged wells and negatively impact human health.
Results from the policy analysis were concluded from the investigation of 19,500 wells. The researchers found that the median costs for decommissioning came to around $20,000 for plugging and $76,000 for surface reclamation and plugging. In rare cases, prices can go well beyond $1 million for each well. The well depth also has a bearing on cost, with every 1,000 feet bringing up costs by 20 percent. Older wells were found to incur a greater cost than more recent wells. The policy analysis also showed that prices varied with surface characteristics between natural gas wells and oil-producing wells across different states.
Understanding the costs and environmental benefits of decommissioning can allow policymakers to develop policies that incentivize the process or instruct companies to bond and decommission their sites and carefully consider the level of taxpayer money that may be used to tackle health and environmental issues.
Storing Waste Heat
The research team chose the Illinois basin oil and gas well to test its geothermal battery because of the nature of subsurface rock formation and the leftover infrastructure of the former well.
Professor Tugce Baser led research concerning the first field demonstration of the geothermal battery in the Illinois Basin. Image used courtesy of the University of Illinois
The basin contains porous, spongelike rock with minerals that provide good thermal conductivity between insulating layers. This environment provides the space and insulation required to set up an artificial heat reservoir that can hold hot fluids for generating electricity.
The researchers injected heated fluid into the porous Cypress Sandstone, situated about 900 meters below the test site surface.
In April 2021, the research team injected water with a temperature reading of 50 degrees Celsius into the well for three days to test the site’s heat storage capacity. Combining test results with numerical modeling revealed a sustained thermal storage efficiency of 82 percent.
The study also revealed an average cost of electricity production of $0.138 per kilowatt-hour.
Given the study’s results, Baser believes that the geothermal battery could be an effective way to store waste heat from industrial sources. Eventually, Baser believes that energy from wind and solar could also be stored.
Repurposing abandoned oil and gas wells in this way could also be a way of saving on decommissioning costs and incentivizing oil and gas companies to turnover and transform their assets to advance the energy transition.