8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Tue 611:23-14:00P9.5Molecular dynamics simulation of the imbibition ofsurfactant solutions in nano-capillaries of varyingroughness and wettabilityEdo Boek 1 and Mikhail Stukan 21 Imperial College, Dept Chemical Engineering, Imperial College SW7 2AZ, London,United Kingdom2 Schlumberger Dhahran Carbonate Research Center, Dammam/Doha Camp,Saudi ArabiaThe spontaneous imbibition of liquid in nano-pores of different roughness and wetting characteristicsis investigated using coarse grained molecular dynamics (MD) simulations. Themolecular-kinetic theory introduced by Blake is used to describe the effect of dynamic contactangle on fluid imbibition. The capillary roughness is modeled systematically using a randomdistribution of coarse grained particles forming the wall. The Lucas-Washburn equation is usedas a reference for analyzing the imbibition curves obtained by simulation. We were able toaccurately define a contact angle by averaging and smoothing the MD data. The results arediscussed in terms of effective hydrodynamic and static capillary radii and their difference as afunction of roughness and wettability [1]. In addition, we determine the impact of surfactants onmodifying the capillary forces in oil-wet nano-capillaries, with or without asphaltenic fractions.Two different wetting states are modeled: 1) Initially oil-wet and 2) Water-wet altered tooil-wet by the presence of hydrophobic asphaltenic components adsorbing on the pore surface.Depending on the interaction potentials between wall, surfactant and asphaltene, we observetwo different mechanisms of surfactant action. First, for relatively weak surfactant-asphalteneinteractions, we find surfactant adsorption at the pore surface making the wall more hydrophilic,aiding water imbibition. Second, for stronger surfactant-asphaltene interactions, we observethat the surfactant emulsifies and removes the adsorbed asphaltene from the capillary wall.This “cleaning” mechanism also leads to improvement in water imbibition. The method canbe used to guide the experimental development of particular surfactants for oil recovery operations.[1] M. R. Stukan, P. Ligneul, J. P. Crawshaw and E. S. Boek, “Spontaneous imbibition ofoil in nanopores of different roughness and wettability”, Langmuir 26, 13342-13352 (2010).5