Hydrogen gas transfer between a borehole and claystone: experiment and geochemical model

The Hydrogen Transfer experiment, located at the Mont Terri underground rock laboratory in Switzerland, is an in situ experimental study of the interactions and transport of hydrogen injected into a borehole installed within Opalinus Clay, a claystone formation. A Python-based model was developed to analyse and model the experimental data, for diffusion of dissolved gases and solutes in claystone pore water, for thermodynamic modelling of gas-water-solid phase equilibria in the injection interval and for simulations of chemical equilibria and reaction kinetics in claystone and injection interval. The developed model reproduces the temporal evolution of gas pressure, composition and solute concentrations measured in situ with a minimum set of adjustable parameters. The effective diffusion coefficients for dissolved gases in Opalinus Clay derived by the modelling of experimental data were found to be very close to values measured in other experimental studies. It was discovered that an accurate description of the temporal variations in hydrogen injection and temporal changes in the inflow of formation water is essential for modelling of microbially mediated hydrogen consumption in the injection interval.

Automated summary

The Hydrogen Transfer experiment conducted at the Mont Terri underground rock laboratory in Switzerland is an in situ study that investigates the interaction and transport of injected hydrogen in Opalinus Clay, a type of claystone formation. A Python-based model was developed to analyze and simulate the experiment's data, including the diffusion of dissolved gases and solutes in claystone pore water, thermodynamic modeling of gas-water-solid phase equilibria, and simulations of chemical equilibria and reaction kinetics. The model accurately reproduces the temporal changes in gas pressure, composition, and solute concentrations measured in situ. The effective diffusion coefficients for dissolved gases in Opalinus Clay derived from the modeling closely match measurements from other experimental studies. The study highlights the importance of accurately describing the temporal variations in hydrogen injection and inflow of formation water for modeling microbially mediated hydrogen consumption in the injection interval.