Visualization of Micro-Particle Retention on a Heterogeneous Surface Using Micro-models: Influence of Nanoscale Surface Roughness

Nanoscale surface roughness and charge heterogeneity have been widely recognized to influence particle retention in porous media under unfavourable chemical conditions such as solutions of low ionic strength (IS) or high pH. However, previous researches have not appreciated the influence of nanoscale surface roughness on particle retention under favourable chemical conditions (e.g. high solution IS). This information is needed to better understand and predict particle transport and retention in such natural environments, such as enhanced oil recovery in a high-salinity reservoir. A glass-etched micro-model was employed to directly visualize retention of micro-sized particles and their spatial distribution on the glass surface under various chemical conditions. The extended DLVO calculations accounting for the effect of nanoscale surface roughness on the interaction energies were employed to quantitatively evaluate the experimental results. It was shown that nanoscale roughness on solid surfaces significantly reduced the strength of primary minimum attachment when the solution IS was high. In particular, increasing the density of roughness on the solid surface increased the strength of primary minimum, whereas increasing the roughness height decreased the strength of primary minimum interaction. Consequently, retained particles in the primary minimum are expected to be susceptible to detachment via hydrodynamic drag forces and movement of air-water interfaces during transient in water saturation (e.g. drainage or imbibition). Indeed, results obtained from the micro-model experiments demonstrated that only a fraction of solid surface was available for particle retention even at a very high IS of 0.6 M.