Underground storage of green gas

A fully sustainable energy system needs large-scale energy storage. Dr Hadi Hajibeygi's proposal for storing green gas in geological formations has won him a Vidi grant from the Dutch research fund NWO.

“I offer a data-informed simulation method for the safe use of underground formations for the cyclic injecting and producing of green fuels,” Hajibeygi promises in his research proposal ADMIRE (stands for Adaptive Dynamic Multiscale Integrated Reservoir Earth simulation method) to NWO. His research expertise is underground fluid dynamics. What looks like impenetrable rock to laymen, is the domain of subsoil streams of gas, oil and water to him. ‘Life is porous’ is his motto.

Underground gas fields are an option for storing renewable energy for months. “We measure capacity in terawatt hours (TWh = 1012 Watthour),” says Hajibeygi. “That is the order of magnitude of a national energy storage – 10 million times more than the capacity of a brand new car battery.” For comparison, energy consumption in the Netherlands is about 800 TWh per year.

The gas reservoir Bergermeer in Alkmaar (Photo: Taqa) 

There is experience with the underground storage of gas, says the Vidi laureate. He mentions the Bergermeer gas reservoir near Alkmaar, which has been used for the commercial seasonal storage of methane since 2014. Elsewhere, hydrogen has been stored in salt caverns. This often involves high pressure (up to 200 bar). In comparison with green methane, hydrogen flows much more easily in porous rocks. While the chance of leakage is higher, the conversions are more direct. A surplus of renewable electricity produces hydrogen by hydrolysis. Hydrogen can be converted back into electricity by a gas engine or a fuel cell. The round-trip efficiency is currently about 40%.

Underground gas storage depends on how the gas flows through the pore spaces in rocks and through the reservoir. Hajibeygi studies these flows by coupling laboratory measurements with large-scale simulations (at kilometre scale with centimetre resolution) and seismic field measurements. His goal is to find suitable locations and safe operational procedures for underground gas storage.

How does he think local people will react to the idea of repeatedly injecting and producing gas from under their feet? “We need to choose wisely where to store it,” says Hajibeygi. “Therefore we need to map, predict and monitor the flow of green gas and the properties of the earth layers.”

In Alkmaar, people initially feared earthquakes when the gas storage was planned, but since the facility is in use, KNMI, the royal meteorological institute, has hardly registered any significant seismic activity.

The ADMIRE project’s first PhD candidate will start soon. Next year, another PhD and a postdoc will follow. With this team, and in collaboration with research labs and universities in Germany, the Netherlands and the United States, Hajibeygi aims to couple modelling and monitoring to reduce the uncertainties about green gas storage.