A monitoring system for monitoring a geological formation includes a casing of an injection well, wherein the casing is configured to extend through an open hole of the geological formation to define an annular space between the casing and the open hole, and wherein the casing includes a mandrel circumscribing at least a portion of the casing, and one or more monitoring lines configured to monitor the geological formation for the presence of carbon dioxide, wherein the one or more monitoring lines are at least partially integrated with the mandrel.

A method of storing hydrogen (H.sub.2) gas in a subsurface formation having an injection well, a production well and a heat well. The method includes injecting a H.sub.2-containing fluid stream into the subsurface formation via the injection well to form a storage composition containing a gas-phase mixture, a liquid-phase mixture and a solid matrix; and heating the subsurface formation containing the storage composition via the heat well thereby achieving a storage condition and maintaining the storage condition. The gas-phase mixture includes 10 to 90% of H.sub.2, 5 to 80% of methane (CH.sub.4), 1 to 10% of carbon dioxide (CO.sub.2), and 1 to 10% of nitrogen (N.sub.2). Each % is based on a total volume of the gas-phase mixture. The liquid-phase mixture includes a water-soluble mineral; and the solid matrix includes clay, shale, slate, and minerals.

Methods for storing hydrogen in subterranean salt caverns using chemical hydrogen carriers.

This disclosure relates to a method and a system for sequestering carbon-containing materials in underground wells. An example method includes: obtaining a material comprising a carbon-containing liquid; optionally testing the material for compatibility with an underground well; optionally adjusting a property of the material to improve the compatibility; and providing the material for injection into the underground well.