Thermodynamic Modelling of Petroleum Fluids

The recent developments and challenges of petroleum thermodynamics are presented in the various papers of this special issue of Oil and Gas Science and Technology (OGST). A common objective of these investigations is the development of calculation tools providing access to reliable thermodynamic as well as thermophysical properties. Hence, this introductory article attempts to put these new developments in a larger perspective by proposing a framework where the practicing engineer can also find some guidelines for the selection, among the large number of existing methods, of the one(s) most suited to his/her industrial application. The analysis is based on the observation that two main features must be present for a good representation of the physical behaviour of complex natural fluids: a model (equation of state – eos- and mixing rules) that represents the physics as well as possible, and an appropriate compositional description. A model is defined as a set of mathematical equations that describes the relationships among different properties. Some are empirical, others are constructed on a physical basis with more or less approximations. All contain parameters that must be determined and validated using experimental data. When accurate properties are required, it is important to focus on the selection of reliable data. However, when predictive power is required (few or no data are available), the use of a model that has a strong physical foundation is essential. The detailed molecular description of a petroleum fluid is often unknown, but even if it were known, it would contain so many isomers that it would be very difficult to handle in an engineering simulator. Hence, several methods are employed to circumvent the problem. The traditional methods are correlations, but we believe they are reaching their limit. New methods, among which molecular simulation, are probably more promising. As a conclusion, we state that both an improved understanding of the physics through experimentation, and an increased use of these physical findings in new models, are the challenges for the future developments of thermodynamics. The papers in this issue illustrate a number of such developments. Les développements récents et les défis nouveaux de la thermodynamique pétrolière sont présentés dans les articles de ce numéro spécial de “Oil and Gas Science and Technology” (OGST). Un des objectifs, commun à ces travaux de recherche, est la mise à disposition d'outils de calcul