Characterization of Heat and Fluid Transport in Porous Media

Characterizing heat and fluid transport in porous media is crucial for many earth science disciplines such as hydrology, glaciology, and volcanology. Heat and fluid transport in porous media are strongly affected by compressing (effective) pressure, which frequently happens in nature (e.g., due to tectonic activities or fluid leakage from a confined acquirer). Therefore, heat or flow characterization requires an understanding of how the thermal and hydraulic properties of porous media are affected by compressing (effective) pressure.

In Askari et al. 1, we introduced a novel method based on pore-scale modeling to simulate heat transfer in granular porous media. One important property that should be included in the numerical modeling of heat transfer is contact resistance, which is the resistance of heat flow in the contact areas between grains. We included the contact resistance in numeral modeling by simulating the deformations of rough grains in the contact areas via the grains’ roughness fractal properties. We showed that for a given compressing pressure, the deformation of the contact areas depends on the fractal dimension that characterizes the grains’ rough surface, as well as Young’s modulus. We also demonstrated that by increasing compressive pressure, thermal conductivity was enhanced more in the grains with smoother surfaces and lower Young’s modulus.

In Ikram et al., we studied the thermal properties of partially saturated porous media is of particular interest to geoscientists in many geological settings such as the vadose zone. We generalized the pore scale model developed by Askari et al. 1 for partially saturated porous media to decipher the effect of fluid saturation on the thermal properties of rocks. For a given compressing pressure, the thermal conductivity was measured at different water saturations. We noted two linear regimes in the dependence of the effective thermal conductivity on the water saturation emerge, separated by a threshold water saturation that signals the formation of a sample-spanning percolation cluster of water-filled pores. The critical water saturation decreased with the increase of the compressing pressure.

In Askari et al. 2, we studied the thermal anisotropy of porous media where anisotropy was initiated with two different mechanisms of grain shape and directional consolidation. We showed that (1) porous media with rougher grains exhibit more thermal anisotropy and (2) the thermal anisotropy decreases with the increase of the compressive pressure.

(a and c) Models of two rough surfaces, I and II. (b and d) Their calculated deformations as a result of a uniform compressing pressure (from Askari et al. 1).

Dependence of the effective conductivity Ke of the granular porous medium, normalized by the conductivity Ks of the solid particles, on the water saturation Sw and the porosity ϕ. Sc denotes the critical saturation for the formation of the sample-spanning cluster of the water phase (from Ikram et al.).