Tech Insights

Can Depleted Fossil Fuel Reservoirs Be Revived for Hydrogen Storage?

May 04, 2024 by Shannon Cuthrell

Subsurface hydrogen storage research explores the possibilities and potential consequences of tapping depleted oil and natural gas reserves for long-duration and seasonal energy storage. 

As a clean and flexible fuel increasingly used in transportation and electricity generation, hydrogen represents a valuable low-carbon resource in the energy transition. However, due to hydrogen’s low volumetric density, large-scale storage is limited. 

Large quantities of hydrogen are difficult to compress. Hydrogen gas can successfully be stored in high-pressure tanks, but its low energy density doesn’t meet the needs of long-range or large-scale applications. Liquid storage also has limitations, requiring cryogenic temperatures to accommodate hydrogen’s low boiling point (-487ºF) at atmospheric pressure. Plus, storage in above-ground vessels is more costly than geologic methods.

 

Testing to determine if hydrogen can be safely stored in depleted oil reservoirs

Testing to determine if hydrogen can be safely stored in depleted oil reservoirs. Image used courtesy of Sandia National Laboratories

 

Alternatively, hydrogen can be stored on solid surfaces through adsorption or within solids via absorption. Underground methods are safer because they separate hydrogen from external risks like floods, ignition sources, or oxygen exposure. Researchers from Sandia National Laboratories are weighing the pros and cons of applying this concept in depleted oil and gas reservoirs for long-term or seasonal storage. 

Salt deposits (specifically salt domes or caverns) are ideal, but such sites are relatively sparse in the U.S. As such, the Sandia team sees promise in repurposing the nation’s many depleted sandstone reservoirs once used for storing oil and gas. It's also considering the potential consequences of hydrogen leaking, becoming contaminated, or getting trapped in the rock. 

 

Storage reservoir maps.

Storage reservoir maps. Image used courtesy of DOE (Slide 11)

 

Why Tap Underground Oil and Gas Infrastructure? 

Underground natural gas storage infrastructure has been used for long-duration storage for over a century, mainly to meet seasonal heating demand. Such sites are widespread throughout the U.S., usually near cities and metro areas with high demand. Facilities that have ceased operations could be reused to hold hydrogen, which has a similar volumetric storage performance as natural gas and supercritical carbon dioxide (CO2). 

 

Underground hydrogen storage methods

Underground hydrogen storage methods. Image used courtesy of DOE 

 

The Department of Energy (DOE)’s National Energy Technology Laboratory has previously estimated U.S. gas storage facilities could enable 327 TWh of pure hydrogen—a significant contribution to the overall demand projected by 2050. Nearly 75% of underground gas storage facilities can store 20% hydrogen-natural gas blends while still satisfying current energy needs. 

However, questions remain regarding the impact of hydrogen gas (H2) blending on underground storage and whether existing facilities can be converted to meet expected demand. Sandia National Laboratories is exploring other practical disadvantages, such as contamination risks, seal integrity, and interactions with residual hydrocarbons left over in oil and gas reservoirs. 

 

Hydrogen Interactions in Shale and Sandstone

In their study, the Sandia team ran experiments predicting interactions between pure H2 and hydrogen and methane (CH₄), a highly flammable greenhouse gas containing carbon and hydrogen. They used nuclear magnetic resonance (NMR) technology to analyze injected H2 into Duvernay shale (mud compressed into rock made of clay-rich mineral particles) and Berea sandstone. Sandstone is a strong candidate because material can easily flow through the gaps between particles.

Then, molecular simulations focused on H2/CH₄ adsorption and diffusion in kerogen, a nanoporous material common in shales. The study identified two H2 populations with distinct NMR responses: free H2 and adsorbed H2. About 10% of injected H2 could be lost due to adsorption/desorption hysteresis in shale, though no H2 loss was found in sandstone. In other words, hydrogen effectively leaves the sandstone when pumped out, but a 10% share of the adsorbed gas remains stuck inside the shale. 

The same researchers published a paper last year studying water and hydrogen interactions in montmorillonite, the type of clay used in oil and gas reservoir shales. The results found limited hydrogen loss and leakage through hydrated interlayers in a subsurface storage system. 

 

Effects of Leftover Oil or Natural Gas 

Sandia’s simulations also found that CH₄ outperformed H2 in kerogen adsorption because it has stronger interactions with the material. Still, about 30% of residual CH₄ could be desorbed after hydrogen is injected into a depleted gas reservoir with low CH₄ pressure. H2 diffusion in porous kerogen is one order of magnitude higher than CH₄ and CO2

This means the reservoir’s rocks could release residual natural gas into the injected hydrogen. Since natural gas contains carbon, a small amount of CO2 would be released when the hydrogen output is burned. 

Other Sandia experiments are now investigating the same phenomenon in depleted oil reservoirs and the potential for hydrogen gas contamination. The findings will inform large-scale field tests. 

1 Comment
  • C
    ChuckD May 10, 2024

    The climate change alarmist are destroying our industrial capability. It’s no longer funny. Oil and gas are best source of cheap energy on the planet. This fact is why the world’s poverty rate has steadily declined since the birth of the industrial age. Until climate change took over and made big impacts on government subsidized boondoggles, the world’s poverty fell below 10% for the first time in history in 2018. Since the adoption of the un-scientific, politically motivated advance of “renewable energy”, the world’s poverty rate has spiked upward. Restricting the availability of cheap energy will do much more harm to the poor and working class of this world than a warm planet ever will.

    Like. Reply