A New Phase Diagram for Fluid Invasion Patterns as a Function of Pore-Scale Heterogeneity, Surface Roughness, and Wettability

Understanding how different flow patterns emerge at various macro- and pore scale heterogeneity, pore wettability and surface roughness is remains a long standing scientific challenge. Such understanding allows to predict the amount of trapped fluid left behind, of crucial importance to applications ranging from microfluidics and fuel cells to subsurface storage of carbon and hydrogen. We examine the interplay of wettability and pore-scale heterogeneity including both pore angularity and roughness, by a combination of micro-CT imaging of 3D grain packs with direct visualization of 2D micromodels. The micromodels are designed to retain the key morphological and topological properties derived from the micro-CT images. Different manufacturing techniques allow us to control pore surface roughness. We study the competition between flow through the pore centers and flow along rough pore walls and corners in media of increasing complexity in the capillary flow regime. The resulting flow patterns and their trapping efficiency are in excellent agreement with previous μ-CT results. We observe different phase transitions between the following flow regimes (phases): (a) Frontal/compact advance, (b) wetting and drainage Invasion percolation, and (c) Ordinary percolation. We present a heterogeneity-wettability-roughness phase diagram that predicts these regimes.