Multi-Phase Equilibrium

The multi-phase equilibrium system considers the interaction potential between fluid and solid components in neighbouring phases and is quantified through the dipole moment and the temperature dependent polarizability of each component. The equilibrium distribution is determined by minimizing the Gibbs free energy for the system of fluid components and phases.

The phases considered are 2 adsorbed film phase (dense liquid & light vapor), and 3 free phases (dense liquid, light liquid, vapor).

The Equation of State is an integral part of the multi-phase equilibrium model and the PVT-fluid properties, incl. viscosity, interfacial tension, and texture dependent properties incl. capillary pressure, and free phase drag forces, are derived from the Equation of State and the interaction potentials.

Alternatively the oil and gas phases are simulated as a multi-component system obeying the vapor-liquid equilibrium laws set forth in Peng-Robinson or Soave-Redlich-Kwong's equation of state (Barrufet, 2003). The oil and gas phases can alternatively be modeled as a black oil model, with the gas phase being methane and the oil phase being selected as a heavy hydrocarbon component disregardless of subsurface pressure and temperature. The fluid components in the multi-component system are selected by the user from a database, which besides from 24 hydrocarbon compounds also includes carbondioxid, hydrogen sulfide, and nitrogen. The source of these non-hydrocarbon compounds is the kerogen, which dependent of kerogen type contains various concentrations of oxygen, sulfur, and nitrogen (Behar & Vandenbroucke, 1987).

The first principles phase equilibrium concept is presented here.