Abstract <p>In this paper, the influence of a wetting liquid adsorption film on the interface morphology and equilibrium kinetics in a solid–liquid–liquid three-phase system located in a slit pore is investigated. Analytical equations are obtained for six possible types of interfacial aggregates at a nonzero adsorption film thickness. The equations describe the surface area of an aggregate, the admissible volume fractions of the nonwetting phase, and the density profiles. Construction of the stability diagram has shown that an increase in the adsorption film thickness narrows the existence region of the of the “worm” type aggregates with the formation of a discontinuity between the “worm” and “roll” regions. The correctness of the density profiles has been confirmed by synthetic data. Molecular dynamics simulation of the calcite–water–<i>n</i>-decane system has revealed that the initial adsorption film of water reduces the time of equilibrium establishment by a factor of two. The presence of the initial layer may lead the system to a local minimum with a higher energy, while imposing no effect on the aggregate shape. Approximating the number density profile by the analytical expression, it has been shown that the adsorption film thickness converges to the equilibrium value regardless of the initial conditions. Thus, allowance for the presence of the adsorption layer is of critical significance for the correct description of aggregate shapes and optimization of simulation time.</p>