Effects of cyclic injection and withdrawal of hydrogen on well systems and reservoir injectivity and productivity: Experiments on sandstones using a scaled-down well system

ABSTRACT: The long term efficiency of underground hydrogen storage operations in porous reservoirs is dependent on the integrity of well systems and properties of the near well reservoirs, such as reservoir injectivity and productivity. In this study, we experimentally investigate the effects of H2 exposure and well pressure cycling on the poroelastic response of casing-cement-sandstone systems using a newly developed scaled-down well system that consists of a steel casing cemented in a hollow porous sandstone sample. It is placed in autoclaves for H2 or N2 exposure, and subsequently in a triaxial apparatus to perform pressure cycling at pressures, temperatures and stresses representative of porous sandstone reservoirs at depths up to ~2.5 km. Both the effect of H2 exposure on the poroelastic response of the sandstone and the integrity of the cement sheath for different hydraulic connectivity between the reservoir/casing and casing-cement interface are analyzed. The results only show minor effects on the response of pore pressure in the sandstone to well pressure cycling. It suggests that effects of pressure cycling on reservoir injectivity and productivity and on well system integrity are limited for the well-cemented, stiff, porous sandstones, and applied conditions including relatively fast cycling over large pressure ranges.