The main objective of this teaching unit is to provide a basic knowledge of gas systems in the geological environment, focusing on the distribution and behavior of gases that will play an important role in the energy transition, such as hydrogen (H2) and helium (He).
The state of the art of the exploration of these gases will be presented and issues concerning the geological mass storage of these gases (salt caverns, aquifers) will be addressed. Necessarily, diffusion properties and interactions with other gases such as hydrocarbon gases and CO2 will be addressed.
More specifically, the storage of gas in salt caverns implies the solubilization of large quantities of evaporites which generally contain high levels of lithium (Li), an element essential to the energy transition for the manufacture of batteries.
In fact, the mastery of the physical and chemical properties and the engineering techniques required to exploit H2, He and Li are largely similar to the methods acquired from experience in the production of hydrocarbons, gas storage and high temperature geothermal energy. The teaching unit will thus also provide basic knowledge of the techniques classically used by the industry.

In summary, the following topics will be covered:

• The major gas systems present on the planet placed in geological contexts.
• Origin, specificities and reactivity of H2. The significance of the isotopic signatures of hydrogen and its associated gases and the reactivity of H2 with carbonaceous compounds will be discussed.
• Origin and specificities of rare gases in general and of He in particular. Use of noble gases (He, Ne, Ar, Kr, Xe) as tracers in the natural environment.
• Origin of lithium and associated compounds
• Industrial uses.

At the end of this unit the student will be able to:

• Define the gas systems present in the geological environment, especially those playing an important role in the energy transition such as hydrogen (H2) and helium (He)
• Identify the problems of solubilisation of evaporites during storage in salt caverns and therefore of leaching of lithium (Li) contained in these rocks
• Describe the techniques for exploiting H2, He and Li traditionally used by the hydrocarbon production, gas storage and high temperature geothermal industries.