Effects of Surface Roughness and Mineral Heterogeneity on Pore-Scale Steam Condensation

ABSTRACT

Sub-pore scale modeling of flow in porous media is gaining momentum. The concept of Digital Core Analysis deals with measurements of virtual core, and the purpose of such modeling is to replace conventional and special core analysis when the latter is not feasible. Single phase flow phenomena are nowadays fairly easy to model given a good representation of the porous mediumby its digital counterpart. One of the challenging concepts in micro-scale simulation of porous media is consideration of phase change phenomena. Mass and heat transfer equations have to be considered simultaneously to capture complexities involved in the evaporation and condensation processes. Therefore, a numerical scheme based on the Volume-of-Fluid method was implemented using the OpenFOAM open-source CFD package along with four phase change models. The aforementioned approach is currently being extended in the modeling of phase change within a porous medium. Surface roughness is introduced by the incorporation of wedges of variable density and amplitude on the pore surface. A further introduced complication is that the individual grains are of different mineralogy and thus of different wettability. The problem of steam condensation in such media is addressed. It is observed that steam condenses first in the smallest of wedges, which act as nucleation sites. Water spreads on water-wet surfaces. Snap-off is observed in several cases leading to temporary trapping of vapor. Grid size effects are also addressed. The application of this modeling effort is the condensation of steam in thermal recovery methods.

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