Pore‐Scale Observations of Hydrogen Trapping and Migration in Porous Rock: Demonstrating the Effect of Ostwald Ripening

We use high-resolution three-dimensional X-ray imaging to study hydrogen injection and withdrawal in the pore space of Bentheimer sandstone. The results are compared with a replicate experiment using nitrogen. observe less trapping because initial saturation after drainage is lower due channeling. Remarkably we that imbibition, if sample imaged again 12 hr, there significant rearrangement trapped hydrogen. Many smaller ganglia disappear while larger swell, no detectable change overall gas volume. For nitrogen, fluid configuration largely unchanged. This facilitated by concentration gradients dissolved aqueous phase—Ostwald ripening, estimate time-scales for this effect be significant, consistent experimental observations. swelling potentially increases connectivity, leading hysteresis more efficient withdrawal.