Underground Storage of H2 and H2-CO2-CH4 Mixtures

In conditions of a natural irreversible reduction in world-wide oil production, the hydrogen is examined as one of the basic sources of the renewable energy able to replace the fossil energies. The underground storage of H2 is considered as a most perspective way to store huge amounts of hydrogen. Various industrial methods usually produces the H2 mixtures with a dominating presence of CO2 and CH4, so the objective of the present research was to analyse various hydrodynamic aspects related to the problem of storing the hydrogen mixtures in porous reservoirs. The storage of H2+CO2+CH4 mixtures like manufactured or civil gas produced by the industrial coal gasification technique represents a double industrial interest, by ensuring, in addition, to capture CO2. When stored in an aquifer, this gas mixture is subjected to an intense bacterial activity. The bacteria consume H2 and CO2 with generating new gases like CH4. Such transformation of the stored gas composition was observed in European civil gas storages. The new model of multicomponent gas injection in reservoir accompanied with chemical reactions and a bacteria population growth is developed, which was next analysed numerically and by using the mathematical methods of the theory of population dynamics. The characteristic parameters like the constants of Monod and Michaelis are obtained by fitting the results of modelling with the in-situ experimental data. Various scenarios of the system evolution are revealed. In particular, an irregular oscillating regime was detected, in which various individual gases can create their owns space accumulations which move in time all along the reservoir. These results are confirmed by in-situ observations. The results of modelling yield optimal regimes of gas injection. The third part deals with using CO2 as a cushion gas for a H2 storage, which may be examined as a new technique of storing large amounts of CO2 in order to reduce the climate changes in the atmosphere. Within the zone of contact between the gases the same chemical-bacteria interactions are observed which leads to a natural reduction of CO2 and a possibility to perform a permanent CO2 injection into the reservoir. Using the mathematical model developed, we have estimated the characteristic rate and the amount of CO2 reduction in time, which determine the main parameters of CO2 injection in practice. <br>