InterPore2026

Exsolution and mixing during hydrogen storage with CO2 cushion-gas in heterogeneous porous media

21 May 2026, 14:05

15m

Oral Presentation (MS08) Mixing, dispersion and reaction processes across scales in heterogeneous and fractured media MS08

Speaker

Dr Maartje Boon (University of Stuttgart)

Description

Underground hydrogen storage typically relies on a cushion gas to stabilize reservoir pressure during cyclic injection, production, and storage. When CO2 is used as a cushion gas, interactions between CO2, H2, and resident brine may influence storage in heterogeneous porous rock.
To investigate this, we conducted microfluidic drainage and imbibition experiments using an equilibrated H2/water system, followed by a storage period under reduced pressure that created supersaturated conditions (water supersaturated with H2). During the storage period, the valve at the chip inlet was closed while the chip outlet was connected to a small reservoir filled with CO2, mimicking a heterogeneous reservoir connected to a CO2 cushion-gas region. A pH indicator was added to the water to visualize the amount of dissolved CO2.
The connection to the CO2 reservoir led to dissolution of CO2 into the water near the outlet, while the brine remained initially supersaturated with H2 near the inlet. This resulted in simultaneous CO2 dissolution and H2 exsolution, with mixing between the two dissolved gas components across the chip.
H2 exsolution at the inlet depleted dissolved H2 and sustained diffusive transport toward the inlet region. This diffusive supply, together with mixing of the two dissolved gas components, maintained continued exsolution, which generated a pressure gradient and led to multiphase flow toward the outlet.
Compared with storage experiments involving only H2, the presence of CO2 cushion gas led to the initial growth of trapped gas ganglia, accelerated the onset of exsolution-driven flow, and promoted intermittent, burst-like invasion events, in contrast to the smoother invasion behavior observed for H2 alone.
These results demonstrate that the choice of cushion gas not only affects the purity of the hydrogen stream but also influences pore-scale fluid redistribution during storage in heterogeneous porous rock.