Experimental investigation of hydrogen breakthrough pressure for a clay-rich caprock

We performed laboratory experiments using customized equipment to measure the breakthrough pressure of hydrogen on plugs retrieved from a clay-rich caprock, named Argille del Santerno Formation. This formation overlies several Italian depleted gas reservoirs currently utilized for natural gas storage but under consideration for conversion into hydrogen storages. After characterizing the caprock (grain size and mineralogy), a set of 9 preserved and fresh plugs was subject to step-by-step tests to measure the breakthrough pressure of hydrogen. To the best of the authors’ knowledge, these are the first reported experiments of breakthrough pressure measurements with hydrogen on plugs obtained from a real caprock. The obtained values range from 25 to 80 bars and compare well to previously reported values for nitrogen and methane, measured on the same caprock under the same testing conditions. Results confirm that hydrogen can be safely stored in the depleted gas reservoirs, even under deltapressure conditions.