Method of storing hydrogen gas in a subsurface formation

A method of storing hydrogen (H2) gas in a subsurface formation having at least one injection well, at least one production well and at least one heat well penetrating the subsurface formation, comprising:

• injecting a H2-containing fluid stream into the subsurface formation via the at least one injection well to form a storage composition containing a gas-phase mixture, a liquid-phase mixture and a solid matrix;
• wherein the gas-phase mixture of the storage composition comprises:
• 10 to 90% of H2;
• 5 to 80% of methane (CH4);
• 1 to 10% of carbon dioxide (CO2);
• 1 to 10% of nitrogen (N2);
• and
• each % is based on a total volume of the gas-phase mixture;
• wherein the liquid-phase mixture of the storage composition comprises at least one water-soluble mineral;
• and
• wherein the solid matrix of the storage composition comprises clay, shale, slate, and minerals;
• and
• heating the subsurface formation containing the storage composition via the at least one heat well thereby achieving a storage condition and maintaining the storage condition.