Micro-CT imaging of drainage and spontaneous imbibition for underground hydrogen storage in saline aquifers
File(s)
Published version
Author(s)
Dokhon, Waleed
AlZaabi, Ahmed
Bijeljic, Branko
Blunt, Martin J
Type
Journal Article
Abstract
This study experimentally investigates hydrogen-brine displacement dynamics in Bentheimer sandstone, with a focus on spontaneous imbibition and its role in underground hydrogen storage in saline aquifers. The displacement is considered in two steps: (1) spontaneous imbibition, where gas is connected and capillary pressure decreases during withdrawal, and (2) brine flooding, where most of the gas is disconnected and the capillary pressure can become negative.
The experiments were conducted using high-resolution micro-CT imaging at 3.1 µm/voxel resolution under 4 MPa and 23 °C conditions. A water-wet porous plate was placed at the outlet to mimic an aquifer source to perform multiple drainage displacements to anchor the irreducible water saturation, followed by spontaneous imbibition, where capillary pressure was reduced incrementally. After reaching Pc = 0, the pressure was maintained for 48 h to observe gas rearrangement via Ostwald ripening at the end of spontaneous imbibition, followed by brine injection to evaluate the gas recovery.
The results showed that spontaneous imbibition led to significant gas snap-off below Pc = 5 kPa, and over 40 % of the initial gas was displaced when Pc reached 0; the gas saturation was 0.51. After the storage time, the initially disconnected large gas clusters became connected across most of the sample’s length. Subsequent brine injection led to some additional gas displacement, with the final gas saturation reaching 0.43. In situ contact angle measurements at Pc = 0 and after brine injection showed an average of 40 °, indicating water-wet conditions, while the H2-brine interfacial curvature was low, consistent with a local capillary pressure of approximately only 1 kPa. Pore occupancy analysis showed gas was initially displaced from narrow pores, with residual gas ganglia trapped in the largest pores, as expected in a water-wet rock. These findings demonstrate that spontaneous imbibition alone can account for a significant fraction of gas displacement above the gas-water contact and should be incorporated into capillary pressure-saturation models.
The experiments were conducted using high-resolution micro-CT imaging at 3.1 µm/voxel resolution under 4 MPa and 23 °C conditions. A water-wet porous plate was placed at the outlet to mimic an aquifer source to perform multiple drainage displacements to anchor the irreducible water saturation, followed by spontaneous imbibition, where capillary pressure was reduced incrementally. After reaching Pc = 0, the pressure was maintained for 48 h to observe gas rearrangement via Ostwald ripening at the end of spontaneous imbibition, followed by brine injection to evaluate the gas recovery.
The results showed that spontaneous imbibition led to significant gas snap-off below Pc = 5 kPa, and over 40 % of the initial gas was displaced when Pc reached 0; the gas saturation was 0.51. After the storage time, the initially disconnected large gas clusters became connected across most of the sample’s length. Subsequent brine injection led to some additional gas displacement, with the final gas saturation reaching 0.43. In situ contact angle measurements at Pc = 0 and after brine injection showed an average of 40 °, indicating water-wet conditions, while the H2-brine interfacial curvature was low, consistent with a local capillary pressure of approximately only 1 kPa. Pore occupancy analysis showed gas was initially displaced from narrow pores, with residual gas ganglia trapped in the largest pores, as expected in a water-wet rock. These findings demonstrate that spontaneous imbibition alone can account for a significant fraction of gas displacement above the gas-water contact and should be incorporated into capillary pressure-saturation models.
Date Issued
2025-10-01
Date Acceptance
2025-07-23
Citation
Advances in Water Resources, 2025, 204
ISSN
0309-1708
Publisher
Elsevier
Journal / Book Title
Advances in Water Resources
Volume
204
Copyright Statement
© 2025 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
License URL
Subjects
CAPILLARY-PRESSURE
Gas displacement
INJECTION
Physical Sciences
Pore-scale processes
Science & Technology
Spontaneous imbibition
Underground hydrogen storage
WATER
Water Resources
X-ray microtomography
Publication Status
Published
Article Number
105064
Date Publish Online
2025-07-24