Clean offshore energy by hydrogen storage in petroleum reservoirs

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. One way to reduce these emissions is to go over to renwable energies to power all the operations and the offshore platforms themselves. However, due to the intermittent nature of renewable energy production such as wind and solar sources, it is necessary to be able to store surplus energy to make it available when production levels drop (e.g. at night or when the wind stops blowing). In the present project we investigate whether energy, in the form of hydrogen (H2), can be stored safely underground in abandoned 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 (chemistry applied to mineral reactions in rocks), geomechanics (solid mechanics applied to porous rocks), materials science and reservoir flow modelling (study of the pore fluid flow in underground rocks) 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 (such as oil-bearing rocks). Through experiments and modelling, the team will study the fundamental interaction of H2 with rocks in the subsurface, reservoir flow and caprock integrity. A student from Ecole Polytechnique in Paris spent 4 months at SINTEF and looked at fatigue effects on cap rock that seals a reservoir, where it is filled and emptied of H2 cyclically. The results show that it is important not to completely empty the reservoir every cycle, otherwise areas around the reservoir are deforming more and more, with the risk of the rock fracturing and a potential leakage path appearing. New simulations were run in 2024 and show the same concentration of deformation in the flanks of the storage site, but give less indication that the caprock can fracture. In the new model, the anisotropy of the caprock was taken into account; This indicates different properties in different directions. The new results have been presented in a hydrogen seminar in Oslo in April 2024 organized by the project's postdoc at UiO, M. Masoudi. Other results from the project were also presented, namely SINTEF Digital's modelling of hydrogen's solubility in water and brine. This is important in order to calculate how much gas is dissolved in the pore water in the storage reservoir, and how much hydrogen can be recovered if needed for each injection cycle. From NORCE, their work on comparison of software to simulate hydrogen flow in porous reservoirs was presented. In the project, UiO has run experimental work where hydrogen adsorption in caprock samples has been measured. The results show that it is important to control for the water saturation in the samples, since it has a major impact on the diffusion and adsorption of the hydrogen. Two master's students from Bremen in Germany, ran H2 exposure of sandstone samples obtained from the Norwegian Offshore Directorate (NOD) in Stavanger. They analyzed the samples after exposure to XRD, X-ray diffraction, a method that provides information about mineral content by measuring how much the radiation is deviated by the material as a function of which crystals the beam has passed through. A new Master's student from Ecole Polytechnique in Paris ran shale samples through exposure to hydrogen, also from NOD, from caprock cores. A more comprehensive test plan was used, where in addition to diffraction tests, fluorescence and combined fluid chromatography with mass spectrometry were run at NTNU. The two additional tests provide information about elemental atoms present in the samples, and minerals that may have been flushed into the pore fluid that has been displaced from the samples through exposure. In addition, reference tests were run with inert argon gas instead of hydrogen. Finally, the samples were subjected to "punch" testing, i.e. the carving of a cylinder while the force needed for extruding it and the deformation that occurs are measured and allow to calculate the shear strength of the material. The same samples were also characterized by measurement of ultrasonic velocities, both with pressure waves and with shear waves at SINTEF. The results show that there is a difference between the reference samples and those exposed to hydrogen, more for sandstone than shale, although the differences are small. Further work on results analyses remains.

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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.