Oil wells may be the solution to one of hydrogen’s biggest problems

To be considered a clean fuel, hydrogen must be green and therefore produced, generally by electrolysis, splitting water through solar or wind energy. It can be used directly feeding engines to generate electricity for industry and in fuel cellspowering electric vehicles and eliminating battery problems.

An additional advantage is that hydrogen can be stored for months and used when energy needs exceed the supply provided by renewable energy sources. However, hydrogen has less energy capacity in a specific volume than carbon-based fuels such as natural gas or propane. Also, compressing it is more complicated. Therefore, Storing large amounts of hydrogen in metal tanks on the surface is not feasible.

Incredibly, the solution comes from oil

In the United States, a team of scientists is investigating, using computer simulations and laboratory experiments, the possibility of using depleted oil and natural gas fields to store hydrogen.

It is already known that hydrogen can be stored underground in salt caverns, but these are not widespread. The chemical engineering team at Sandia National Laboratories, Tuan Hodirector of the research, is studying whether the hydrogen stored in depleted oil and gas fields will be trapped in the rock, will leak or become contaminated.

The objective is to ensure that hydrogen stays where it is injected to avoid losses and guarantee storage efficiency, they explain in a statement and in an article published in the International Journal of Hydrogen Energy. “In summer it is possible to produce a lot of electricity with solar energy, but it is not needed. The excess can be converted into hydrogen and stored until winter,” he adds.

The step-by-step investigation

Ho’s team studied whether hydrogen would become trapped in sandstone or shale that forms the body and would seal many oil and gas deposits or, on the contrary, would leak.

The sandstone It is made up of sand-sized grains of minerals and rocks that have been compressed over eons. It has many spaces between particles and can therefore store water in aquifers or form oil and gas reservoirs. He shale It is mud compressed into rock and is made up of much smaller particles of clay-rich minerals. Therefore, shale can form a seal around sandstone, trapping oil and natural gas. This way, the injected hydrogen remains in the same place and is not lost.

They used experiments to study how hydrogen interacts with samples of sandstone and shale. They found that the hydrogen does not remain inside the sandstone after being pumped, but up to 10% of the adsorbed gas is trapped inside the shale sample. These results were confirmed by computer simulations performed by Ho.

By taking a closer look at a specific type of clay, which is common in shale around oil and gas fields, Ho performed virtual simulations of the molecular interactions between layers of montmorillonite clay, water and hydrogen. He discovered that hydrogen does not penetrate the watery spaces between the mineral layers of that type of clay.

This means that the loss of hydrogen in the clay due to getting stuck or moving through it is small and confirms the viability of underground hydrogen storage. These clay findings were published last year in the journal Sustainable Energy and Fuels. Additional absorption experiments are currently being performed at Stevens Institute of Technology and the University of Oklahoma to confirm the molecular simulation results.

Using experiments and simulations, Ho’s team discovered that residual natural gas can be released from the rock into hydrogen when it is injected into a depleted natural gas reservoir. This means that when the hydrogen is removed for use, will contain a small amount of natural gas. Therefore, it is important to keep in mind that when that hydrogen is burned it will also produce a small amount of carbon dioxide.

Currently, and through simulations and molecular experiments, Ho’s team is studying the effects of hydrogen on a depleted oil field and how the leftover could contaminate or interact with it. But additional research is still needed to understand how microorganisms and other chemicals in depleted oil reservoirs might interact with stored hydrogen.