Method to estimate the influence of pore-size distribution on phase equilibrium of multi-component hydrocarbon systems in unconventional shale gas and oil reservoirs

A method for estimating liquid and vapor molar fraction of components, liquid mole fraction, vapor mole fraction, liquid saturation, and vapor saturation of a mixture of hydrocarbons in nano-pores in an earth formation includes: constructing an equation of state (EOS) representing the mixture hydrocarbons in the nano-pores in the earth formation; the EOS having a term accounting for capillary pressure in the nano-pores. The method further includes inputting a composition of the mixture of hydrocarbons, a phase pressure of the hydrocarbons and a pore size distribution of the earth formation into the EOS and solving the EOS and to estimate the liquid and vapor molar fraction of components, liquid mole fraction, vapor mole fraction, liquid saturation, and vapor saturation of the mixture of hydrocarbons in the nano-pores in the earth formation.