Emissions from petroleum production account for over 25% of Norway’s total CO2 emissions, and these must be significantly reduced to meet Norway’s ambitions in the Paris Agreement. One way to reduce these emissions is to switch to renewable energy to power all operations and offshore platforms. However, due to the variable supply of renewable energy such as wind and solar, it is necessary to be able to store excess energy to make it available when production levels decrease (e.g. at night or when the wind stops blowing). In this project, we investigated whether energy, in the form of hydrogen (H2), can be safely stored underground in produced oil and gas reservoirs. These are widely available in Norway, and their use for H2 storage could open up a renewable offshore future for the country. The project included both experiments and modeling to study the interaction between H2 and subsurface rocks, reservoir flow and caprock integrity. A student from Ecole Polytechnique in Paris spent 4 months at SINTEF looking at fatigue effects on cap rock that seals a reservoir, where it is cyclically filled and emptied of H2. The results show that it is important not to completely empty the reservoir each cycle, otherwise areas around the reservoir will deform more and more, with the risk of the rock fracturing, and a potential leakage path will arise. New simulations were run in 2024 and show the same concentration of deformation in the flanks of the storage site, but indicate less likelihood that the caprock may fracture. In the new model, the anisotropy of the caprock was taken into account; this implies different properties in different directions. In Oslo, a seminar was organized by the project’s postdoc at the University of Oslo (UiO), M. Masoudi, in April 2024. There, results from the project were presented, including SINTEF Digital’s modeling of hydrogen solubility in water and saltwater. This is important for calculating how much gas dissolves into the pore water in the storage reservoir, and how much hydrogen can be retrieved again during each injection cycle. From NORCE, their work on comparing software for simulating hydrogen flow in porous reservoirs was presented. SINTEF’s modeling of caprock fatigue and other invited contributions, such as NORCE’s projects on H2 and research conducted by the University of Edinburgh, were also presented. UiO has conducted experimental work in the project where hydrogen adsorption in caprock samples has been measured. The results show that it is important to control for water saturation in the samples, as it significantly affects the diffusion and adsorption of hydrogen. Two master’s students from Bremen, Germany, conducted H2 exposure tests on sandstone samples obtained from the Norwegian Offshore Directorate in Stavanger. They analyzed the samples after exposure using XRD (X-ray diffraction), a method that provides information about mineral content by measuring how much the radiation is diffracted by the material as a function of the crystals the beam has passed through. A new master’s student from École Polytechnique in Paris exposed shale samples to hydrogen, also from the Norwegian Offshore Directorate, taken from caprock cores. A more extensive test plan was used, where in addition to diffraction tests, fluorescence and combined fluid chromatography with mass spectrometry were conducted at NTNU. These two additional tests provide information about elemental atoms present in the samples and minerals that may have been flushed into the pore fluid displaced from the samples during exposure. In addition, reference tests were conducted using inert argon gas instead of hydrogen. Finally, the samples were subjected to “punch” testing, i.e., cutting out a cylinder while measuring the force required and the resulting deformation, which allows for calculating the shear strength of the material. The same samples were also characterized by measuring ultrasonic velocity, both with pressure and shear waves, at SINTEF. The results show that there is a difference between the reference samples and those exposed to hydrogen—more so for sandstone than shale—even though the differences are small. The conclusion from the project is that exposure to H2 has the greatest effect on reservoir rock, depending on its mineralogy, while it has less effect on the sealing caprock. However, fatigue effects during injection and production are still important, in light of the different responses between the reservoir and the surrounding sealing layers; this should be further investigated through experimental work in new projects.
Hydrogen storage has the potential of increasing the amount of renewable power that can be used for powering offshore platforms. In the long run it can even enable zero-emission petroleum production on the Norwegian Continental Shelf. This will be needed in a future where it is foreseen that hydrocarbons are not burnt, but instead used solely as raw materials in the production of important goods such as plastics, paints, textiles, pharmaseuticals and asphalt. Results from the project show that offshore storage in depleted fields looks promising, as no showstoppers have so far been uncovered. Provided that fatigue effects and deformation of the storage complex can be monitored closely, it should be possible to store vast amounts of hydrogen in these reservoirs. Remediation upon early warning of accumulating rock deformation around the reservoir could be reduction of stored volume, or increase in cushion gas volume. This would reduce the pressure fluctuation levels in the reservoir pore fluid, and ensure no transmitted accumulation of plastic deformation in the caprock. These encouraging results for the feasibility of pure H2 storage offshore, may lead to rapid achievement of EU ambitions of a carbon-neutral energy supply.
Emissions from petroleum production stand for over 25% of Norway's total CO2 emissions, and these must be significantly reduced for the country to reach its ambitions in the Paris Agreement. Powering offshore platforms by renewables is thus an important goal, but it relies on large-scale energy storage options for balancing out the mismatch between power supply and demand. In the present project we investigate whether energy, in the form of hydrogen (H2), can be stored safely underground in depleted oil and gas reservoirs. These are widely available in Norway, and their use for H2 storage can open for a renewable offshore future for the country by powering petroleum platforms. The project involves a national team of world-renowned experts in the fields of geochemistry, geomechanics, materials science and reservoir flow modelling from SINTEF, NORCE and the University of Oslo, and an international research partner from Queen Mary University of London, an acclaimed expert in oilfield chemistry and flow in porous media. Through experiments and modelling, the team will study the fundamental geochemical effects of H2 in the subsurface, reservoir flow and caprock integrity. This will give a first indication on whether future, more applied, research projects should be initiated on the topic.
