Understanding the properties of a fluid / shale formation is important for fluid-in-place estimation and productivity prediction. The fluid is mainly trapped in organic nanoporous material called kerogen and behaves differently from bulk fluid due to the effect of confinement and interactions with pore walls. The inhomogeneity in density distribution causes different adsorption behavior from bulk and the solvation of hydrocarbon in solid phase results in absorption, which both affect the fluid-in-place prediction. Further, the shifted phase boundaries affect the hydrocarbon production response.
Inhomogeneous statistical associating fluid theory (iSAFT) has been successful in modeling inhomogeneous fluids. In this work we use iSAFT to calculate the density distribution and phase envelope of hydrocarbon mixtures (C1-C5) in nano slit pores. Although the slit pore model is rather idealized compared to the complex composition and structure in shale pores, it provides information on confined multicomponent phase behavior, an area which is lacking in the literature. The adsorption isotherm and capillary condensation of pure component and mixture is studied. By modeling the wall as hard repulsive, attractive (activated carbon) and permeable (organic compound) walls and varying the pore size, we investigate the influence of pore wall on the phase transitions.