Chapter 7: Thermodynamics and Phase Behavior

Phase behavior describes the complex interaction between physically distinct, separable portions of matter called phases that are in contact with each other. Typical phases are solids, liquids, and vapors. Phase behavior plays a vital role in many petroleum applications, such as enhanced oil recovery, compositional simulation, geochemical behavior, wellbore stability, geothermal energy, environmental cleanup, multiphase flow in wellbores and pipes, and surface facilities.

Thermodynamics, which is central to understanding phase behavior, is the study of energy and its transformations. Using thermodynamics, we can follow the energy changes that occur during phase changes and predict the outcome of a process. Thermodynamics began as the study of heat applied to steam power but was substantially broadened by Gibbs in the middle to late 1800s. Gibbs’ most significant contribution was the development of phase-equilibrium thermodynamics applied to multicomponent mixtures, particularly the concept of chemical potential. ¹  The concept of chemical potential leads to the result that, at equilibrium, the chemical potential of each component must be the same in all phases ( μ _iL = μ _iV ).