Process-Dependent Solute Transport in Porous Media

Abstract

Solute transport under single-phase flow conditions in porous micromodels was studied using high-resolution optical imaging. Experiments examined loading (injection of ink-water solution into a clear water-filled micromodel) and unloading (injection of clear water into an ink-water filled micromodel). Statistically homogeneous and fine-coarse porous micromodels patterns were used. It is shown that the transport time scale during unloading is larger than that under loading, even in a micromodel with a homogeneous structure, so that larger values of the dispersion coefficient were obtained for transport during unloading. The difference between the dispersion values for unloading and loading cases decreased with an increase in the flow rate. This implies that diffusion is the key factor controlling the degree of difference between loading and unloading transport time scales, in the cases considered here. Moreover, the patterned heterogeneity micromodel, containing distinct sections of fine and coarse porous media, increased the difference between the transport time scales during loading and unloading processes. These results raise the question of whether this discrepancy in transport time scales for the same hydrodynamic conditions is observable at larger length and time scales.

Effect of Pore‐Wall Roughness and Péclet Number on Conservative Solute Transport in Saturated Porous Media

“…Interestingly, the exponent 1.09 is very close to 1.07 reported by Erfani et al. (2021) who investigated solute transport under loading and unloading conditions. The exponent 1.09 is also consistent with laboratory observations, which indicated that for practical purposes the exponent relating dispersion coefficient to average velocity can be set equal to unity for granular materials (Freeze & Cherry, 1979).…”

Impact of Displacement Direction Relative to Heterogeneity on Averaged Capillary Pressure‐Saturation Curves

“…Figure 1 shows the micromodel composed of two distinct sections, referred to as coarse and fine sections, with identical dimensions. The coarse and fine section permeabilities were 42 × 10 −12 and 23 × 10 −12 m 2 , respectively, estimated using the single‐phase Navier‐Stokes equation implemented in OpenFOAM ® with the same statistics for the solid cylinders of the micromodel (Erfani et al., 2021). The grain shape in both sections was circular in planar view, creating pores with a variable rectangular cross‐section.…”

“…The heterogeneity interface was located in the middle of this window. Moreover, the representative elementary volume (REV) size was estimated (based on porosity and permeability measurements) to be about 4 and 3 mm for the coarse and fine sections, respectively (Erfani et al., 2021).…”