Effect of Saturation and Image Resolution on Representative Elementary Volume and Topological Quantification: An Experimental Study on Bentheimer Sandstone Using Micro-CT

Abstract

Plots show the REV of the specific interfacial area and corresponding relative error as compared to the benchmark results obtained at voxel size equal to 1.66 𝜇m for phase pair (a-b) air-brine, (c-d) air-grain, and (e-f) grain-brine found at 𝜖 𝑐 =0.05 for all the data sets at varying image resolution. The REV is not found for I02 and I03 at larger voxel size for the phase pairs air-brine and also for I02 for phase pair grain-brine due to the preferential loss of small brine features.

Characterization of Liquid‐Vapor Interfaces in Pores During Evaporation

“…In fact, smaller diameter of glass beads or sand requires much smaller image voxels to ensure accurate recognition of edges or interfaces. As described in Huang et al (2021), the SIA of air and grain decreases sharply as the size of image voxel increases when the image resolution is coarsened. Further, the development of the l-v interfacial area with water saturation implies strong correlations to the interparticle stress development (Lu & Likos, 2006) and enhanced thermal conduction or vapor flux at elevated temperatures (Cass et al, 1984;Shahraeeni & Or, 2012).…”

Evolution of Bentheimer Sandstone Wettability During Cyclic scCO2‐Brine Injections

“…A low-resolution scan (voxel size 19.7 μm) was acquired to ensure complete saturation of the core at this pressurized state; after this, the core was flushed again at low flow rate (0.05 ml/min) with 25 ml scCO 2 -saturated 1.0 M KI brine (this "live" brine had been mixed with scCO 2 under working temperature and pressure for 𝐴𝐴 𝐴 48 h), and another low-resolution scan was acquired to again confirm complete saturation of the core with brine. At this point, drainage (scCO 2 injection)-imbibition (brine injection) cycles commenced, with radiograph-based time-lapse sequences acquired during pumping and a full 3D high-resolution Region-of-Interest ("ROI") scan (Huang et al, 2021;Latham et al, 2008Latham et al, , 2018Myers et al, 2011) acquired at the endpoint of every flow process (i.e., after cessation of flow and at least one hour of equilibration time). The imbibition flow rate was chosen to approximate the capillary number of the experiments of Herring et al (2016), assuming the conventional macroscopic definition 𝐴𝐴 𝐴𝐴𝐴𝐴 = 𝜇𝜇×𝑣𝑣 𝜎𝜎 ; where μ is the invading fluid viscosity, v is the invading fluid interstitial velocity, and σ is the scCO 2 -brine interfacial tension; note that this corresponds to a relatively high injection flow rate for a geologic injection.…”

Hierarchical Homogenization With Deep‐Learning‐Based Surrogate Model for Rapid Estimation of Effective Permeability From Digital Rocks

“…The volume size is 1,200 × 1,200 × 5,000 (∼7.2 billion voxels) and the imaging resolution is 1.65 μm. The micro‐CT image corresponds to a physical volume of 32.77 mm 3 , which is sufficient to reach the representative elementary volume (REV) (Huang et al., 2021). The porosity computed from the micro‐CT image is 23% and the correlation lengths in the x , y , and z directions are 19.69, 27.64 and 11.05 voxels, respectively (Figure 11b and Table 1).…”