Pore-scale capillary pressure analysis using multi-scale X-ray micromotography

Abstract

A multi-scale synchrotron-based X-ray microtomographic dataset of residually trapped air after gravity-driven brine imbibition was acquired for three samples with differing pore topologies and morphologies;image volumes were reconstructed with voxel sizes from 4.44 µm down to 0.64 µm. Capillary pressure distributionsamong the population of trapped ganglia were investigated by calculating interfacial curvature in order to assess the potential for remobilization of residually-trapped non-wetting ganglia due to differences in capillary pressure presented by neighbor ganglia. For each sample, sintered glass beads, Boise sandstone and Fontainebleau sandstone, sub-volumes with different voxel sizes were analyzed to quantify air/brine interfaces and interfacial curvatures and investigate the effect of image resolution on both fluid phase identification and curvature estimates. Results show that the method developed for interfacial curvature estimation leads to reliable capillary pressure estimates for gas ganglia. Higher resolution images increase confidence in curvature calculations, especially for the sandstone samples that display smaller gas-brine interfaces which are then represented by a higher number of voxels when imaged with a micron or sub-micron voxels size. The analysis of subvolumes from the Boise and Fontainebleau dataset highlights the presence of a residuallytrapped gas phase consisting of ganglia located in one or few pores and presenting significantly different capillary pressures, especially in the case of Fontainebleau sandstone. As a result, Ostwald ripening could occur, leading to gas transfer from ganglia with higher capillary pressure to surrounding ganglia with lower capillary pressures. More generally, at the pore-scale, most gas ganglia do present similar capillary pressures and Ostwald ripening would then not represent a major mechanism for residually-trapped gas transfer and remobilization.

Gravity‐Induced Bubble Ripening in Porous Media and Its Impact on Capillary Trapping Stability

“…This observation agrees with previous experimental studies in the absence of gravity (Garing et al, 2017;Xu et al, 2017). This observation agrees with previous experimental studies in the absence of gravity (Garing et al, 2017;Xu et al, 2017).…”

“…At equilibrium, Ostwald ripening leads to the formation of a single large bubble that may become hydrodynamically unstable (Fu et al, 2016). This observation has been confirmed by recent pore-scale (Xu et al, 2017) and core-scale (Garing et al, 2017) experiments and pore-scale modeling (de Chalendar et al, 2018). This observation has been confirmed by recent pore-scale (Xu et al, 2017) and core-scale (Garing et al, 2017) experiments and pore-scale modeling (de Chalendar et al, 2018).…”

Validation of model predictions of pore-scale fluid distributions during two-phase flow

“…Despite the variability in the fluid distribution on a pore-bypore basis, averaged properties such as residual gas saturation (0.320 ± 0.010), trapped gas cluster sizes (fitted Fisher exponent 2.106 ± 0.011), and nonwetting phase Euler numbers did not show strong variability in the experiments investigated here [32], nor in other experiments in the literature [58][59][60]. This suggests that the different pore-scale fluid distributions in the experiment are statistically similar and have globally similar connectivity properties.…”

The Impact of Pore‐Scale Flow Regimes on Upscaling of Immiscible Two‐Phase Flow in Porous Media

“…Concurrent improvements of X‐ray microtomography combined with its nondestructive features have allowed direct visualization of pore‐scale structures and distribution of phases as inputs to computational models. A number of authors have investigated pore‐scale phases distribution using X‐ray microtomography and demonstrated the complexity of the nonwetting and wetting phase interface geometry (e.g., Armstrong et al, ; Blunt et al, ; X. Chen & DiCarlo, ; X. Chen et al, ; Gao et al, ; Garing et al, ; Moghadasi et al, ; Prodanovic et al, , ; Reynolds et al, ).…”