Speaker
Description
Hydrogen (H2) storage in underground porous media could support the energy transition by acting as an energy store to balance supply and demand in the renewable energy sector. Important unknowns to this technology include the H2 fluid flow through a porous medium which affects the H2 injectivity and recovery. We used time-resolved X-ray micro-computed tomography to image unsteady and steady-state injections of H2 and brine (2 M KI) into a Clashach sandstone core at 5 MPa and ambient temperature (Clashash composition: ~96 wt.% quartz, 2% K-feldspar, 1% calcite, 1% ankerite).
During steady-state injections, initial entry of H2 into the brine-saturated rock was within seconds, with H2 dispersing into several discrete pores. Over time, some H2 ganglia connected, disconnected and then reconnected (intermittent flow), indicating that the current anticipation of a constant connected flow pathway during multiphase fluid flow may be an oversimplification. Pressure oscillations at the core outlet during steady-state experiments were characterized as red noise, confirming observations of intermittent pore-filling. At higher H2 fractional flow the H2 saturation in the pore space increased from 20-22% to 28%. The average Euler characteristic was generally positive over time, indicating poorly connected H2 clusters and little control of connectivity on the pore space H2 saturation. During unsteady-state injections, H2 displacement of brine included Haine’s jumps.
Dynamic fluid rearrangements such as intermittent flow and Haine’s jumps are outside the framework of Darcy’s law extended to multiphase flow. However, the evolution of H2 saturation with H2 fractional flow could still be described using the conventional framework of relative permeability functions, suggesting that the large-scale movement of H2 was not affected by intermittent flow. Yet, never previously has intermittent flow been documented at low capillary numbers of 4.7 ×10-9. Due to the high viscosity ratio of the H2-brine system intermittent flow may be relatively more important than for nitrogen or oil.
Our results suggest a lower H2 storage capacity in sandstone aquifers with higher injection- induced hydrodynamic flow and suggest a low H2 recovery. For more accurate predictions of H2 storage potential and recovery, geological models should incorporate energy dissipating pore-scale processes such as Haine´s jumps and intermittent flow.
| Country | Spain |
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