The scientific basis of hydrogen storage in the environment, the causes and mechanisms of its interaction with other natural gases and fluid-containing media are poorly developed. Therefore, it is important to conduct a set of studies aimed at clarifying the main factors of its storage in UGS facilities together with methane. Changes in the physico-chemical properties of a sandstone sample after prolonged exposure to a hydrogen-methane mixture have been studied using infrared spectroscopy (IR), nuclear magnetic resonance (NMR), X-ray fluorescence analysis, and velocity measurement of longitudinal and transverse sound waves. Changes in the composition of the rock are confirmed by differences in the IR, NMR, and transformation spectra of the mineral component of sandstone, which is largely due to the crystallization processes of substances dissolved in adsorbed water. The results of these studies can be used in the planning and operation of underground gas storage facilities in regions where large-scale hydrogen production and storage will be organized.