Quantification of capillary trapping of gas clusters using X-ray microtomography

Abstract

A major difficulty in modeling multiphase flow in porous media is the emergence of trapped phases. Our experiments demonstrate that gas can be trapped in either single-pores, multipores, or in large connected networks. These large connected clusters can comprise up to eight grain volumes and can contain up to 50% of the whole trapped gas volume. About 85% of the gas volume is trapped by multipore gas clusters. This variety of possible trapped gas clusters of different shape and volume will lead to a better process understanding of bubble-mediated mass transfer. Since multipore gas bubbles are in contact with the solid surface through ultrathin adsorbed water films the interfacial area between trapped gas clusters and intergranular capillary water is only about 80% of the total gas surface. We could derive a significant (R 2 5 0.98) linear relationship between the gas-water-interface and gas saturation. We found no systematic dependency of the front velocity of the invading water phase in the velocity range from 0.1 to 0.6 cm/min corresponding to capillary numbers from 2 3 10 27 to 10 26 . Our experimental results indicate that the capillary trapping mechanism is controlled by the local pore structure and local connectivity and not by thermodynamics, i.e., by the minimum of the Free Energy, at least in the considered velocity range. Consistent with this physical picture is our finding that the trapping frequency (5 bubble-size distribution) reflects the pore size distribution for the whole range of pore radii, i.e., the capillary trapping process is determined by statistics and not by thermodynamics.

Quantification of Gas‐Phase Trapping within the Capillary Fringe Using Computed Microtomography

“…The distribution of capillary fingers and the probability of creating such loops in the capillary zone are controlled only by the connectivity of the pore space, while capillary forces dominate over viscous fingering induced by the water table rise. The same results were also reported by others in two‐dimensional micromodels (Chatzis, 1995) and three‐dimensional columns (Geistlinger et al, 2014).…”

“…So, as discussed above, deviation from single‐pore trapping increases in finer sediments, which results in increasing gas interfacial area. Although not all of this interface may be in direct contact with the wetting fluid (water) (Dalla et al, 2002; Geistlinger et al, 2014), it significantly affects the rate of mass transfer between fluids in porous media, especially at early times. These quantities, combined with cluster size frequencies, can be used to improve dissolution process modeling and prediction.…”

“…The actual rising velocity, however, was measured by using a bypass tube connected to the bottom of the column. It showed the location of the free water level (Geistlinger et al, 2014). Minor differences were observed between the adjusted and measured velocities.…”

Pore‐scale investigation of effects of heterogeneity on CO2 geological storage using stratified sand packs

“…This was because that we used well‐sorted, larger sands with similar grain size, resulting in the residual CO 2 being easily displaced during imbibition, while in other studies, smaller size or sintered glass beads were employed . Also, we conducted our experiments at a lower temperature and pressure than the studies which finding capillary trapping in glass beads . Parameters such as pressure, temperature, and salinity conditions, which impact the fluid properties and interaction of the CO 2 ‐brine system, significantly influence the procedures of capillary trapping.…”

Quantification of hysteresis effects on a soil subjected to drying and wetting cycles

“…Local pore structure and local connectivity plays a leading role in the trapping mechanism (Geistlinger et al, 2014). Due to the trapping mechanism caused by the main wetting process, using method 2 (Eq.…”