Abstract
The solubility of hydrogen (
H
2
) was experimentally determined in pure water, NaCl solutions, and deep reservoir brines from the Ketzin site using a high-pressure autoclave setup. Experiments were conducted at temperatures up to 373.15 K and pressures up to 200 bar, covering conditions relevant for underground hydrogen storage. Hydrogen solubility increases with pressure, whereas temperature effects are comparatively moderate and partly non-monotonic. Measurements in pure water reproduce literature data and confirm the characteristic temperature inversion behavior of hydrogen dissolution. In saline systems, a pronounced salting-out effect reduces hydrogen solubility relative to pure water. This effect becomes stronger in the complex Ketzin brines, where increasing ionic strength and multi-ion composition further suppress the temperature sensitivity of hydrogen dissolution. At reservoir-relevant conditions, only a small fraction of injected hydrogen is expected to dissolve into the formation brine. A key outcome of this work is the generation of the first experimentally determined hydrogen solubility dataset for natural multi-ion reservoir brines. The dataset provides an experimental basis for future thermodynamic and reservoir-scale modeling studies, supports the assessment of dissolution-driven hydrogen losses, and contributes to reducing uncertainties in the evaluation of underground hydrogen storage performance.