Effect of Nanoscale Surface Textures on Multiphase Flow Dynamics in Capillaries

Abstract

Multiphase flow through porous media is important in a wide range of environmental applications such as enhanced oil recovery and geologic storage of CO2. Recent in situ observations of the three-phase contact line between immiscible fluid phases and solid surfaces suggest that existing models may not fully capture the effects of nanoscale surface textures, impacting flow prediction. To better characterize the role of surface roughness in these systems, spontaneous and forced imbibition experiments were carried out using glass capillaries with modified surface roughness or wettability. Dynamic contact angle and interfacial speed deviation, both resulting from stick-slip flow conditions, were measured to understand the impact these microscale dynamics would have on macroscale flow processes. A 2k factorial experimental design was used to test the ways in which the dynamic contact angle was impacted by the solid surface properties (e.g., wettability, roughness), ionic strength in the aqueous phase, nonaqueous fluid type (water/Fluorinert and water/dodecane), and the presence/absence of a wetting film prior to the imbibition of the wetting phase. The analysis of variance of spontaneous imbibition results suggests that surface roughness and ionic strength play important roles in controlling dynamic contact angle in porous media, more than other factors tested here. The presence of a water film alone does not affect dynamic contact angle, but its interactions with surface roughness and aqueous chemistry have a statistically significant effect. Both forced imbibition and spontaneous imbibition experiments suggest that nanoscale textures can have a larger impact on flow dynamics than chemical wettability. These experimental results are used to extend the Joos and Wenzel equations relating apparent static and dynamic contact angles to roughness, presence of a water film, and water chemistry. The new empirical equation improves prediction accuracy by taking water film and aqueous chemistry into account, reducing error by up to 50%.