Multicomponent Shan Chen pressure boundary

Hi guys,
I’m trying to simulate two phase displacement in a porous medium and obtain capillary/pressure vs saturation curve by means of the Shan Chen multicomponent model in Palabos. The problem I encountered is that there is no stable boundary condition for this model except periodic and bounceback. In the paper “Lattice-Boltzmann simulation of two-phase flow in porous media” of Pan et. al they used some pressure boundary condition, but they do not specified how!!!Any suggestions? In order to bypass this obstacle, I thought to use periodic BC with a body force applied only to the injected phase, with budder layer before and after the porous media. In this case I have displacement, but I don’t know if it has a physical meaning and most of all how to compute capillary pressure.
Thank you in advance