Depleted oil fields could be used to contain liquid hydrogen as much of the infrastructure already in place can be repurposed, researchers at King Abdullah University of Science and Technology (KAUST) have said.

Hydrogen is a clean-burning gas that could help to tackle climate change by reducing our dependence on fossil fuels as it can be produced from water using renewable energy. But storing and transporting the gas is typically very expensive and involves a number of technical challenges such as high-pressure gas tanks or cryogenic systems that operate at very cold temperatures.

The oil industry is currently in a peak period of decommissioning, with assets installed between the late 1970s and early 1990s reaching the end of their 30-40-year design lives. The decommissioning market is also expected to grow by as much as 8% a year over the next decade. There are some metrics that suggest the world has surpassed ‘peak oil’, as other sources of energy and technology such as electric vehicles become more commonplace.

According to the KAUST team, infrastructure can be repurposed if hydrogen is incorporated into carbon-based molecules known as Liquid Organic Hydrogen Carriers (LOHCs), which are safer and easier to handle than the gas itself. 

“These advantages make LOHCs a compelling alternative to conventional hydrogen storage technologies,” said Hussein Hoteit, who led the research team.

LOHC systems use a catalyst to chemically combine hydrogen with a liquid organic molecule, forming a hydrogenated liquid that can be stored or transported like a conventional fuel. A second catalytic reaction is subsequently used to release the hydrogen and regenerate the initial carrier molecule.

The liquid can be handled using existing petrochemical infrastructure, such as pipelines, tankers and large-scale storage facilities. 

“This significantly reduces the cost and complexity of building new hydrogen-specific infrastructure, which is one of the major barriers to widespread hydrogen deployment,” said Zeeshan Tariq, a member of the team.

The researchers simulated how two different LOHC systems would perform in a depleted sandstone reservoir at a depth of about 2,200 metres, typical of oil fields in Saudi Arabia. Their calculations included a wide range of factors, including the viscosity, stability and hydrogen-storage capacity of the LOHC molecules.

One of the liquids trialled, known as methylcyclohexane, was injected into the reservoir for five months, left for two months, and then extracted over five months. The year-long cycle was repeated 15 times. Calculations suggest that about three-quarters of the methylcyclohexane could be recovered after each cycle. 

By the end of the simulation, more than half of the residual oil trapped in the field had also been recovered. This additional oil would offset storage costs, and the researchers estimate that the whole project would generate $70m more in value than it consumed.