Shale caprock integrity under coupled stress and gas pressure from in-situ SANS: Implications for gas storage

A comprehensive understanding of stress effects on the nano- to sub-micropore structure and fluid flow in shales is essential for evaluating their suitability in subsurface gas storage applications, including hydrogen. An in-situ Small Angle Neutron Scattering (SANS)-based experimental framework is established to evaluate nanostructure evolution and gas transport in Velkerri Formation shales under the synergistic effects of uniaxial stresses (up to 600 bar) and deuterated methane (CD 4 , 500 bar) cycling, providing a proxy for assessing caprock integrity and storage efficiency. Results show that a single uniaxial stress loading–unloading may enlarge smaller pores and promote larger pore formation through stress-induced coalescence of adjacent nanopores, while possibly facilitating the expulsion of confined methane. The extent of irreversible modification is sample-specific. CM-CD 4 sorption–desorption may further modify stress-weakened nanostructures. A post-mature, organic- and clay-lean, quartz-rich sample exhibits the strongest caprock potential among the studied samples, based on mechanical stability, petrophysical behaviour, and mineralogy.