Thermodynamic properties of petroleum fluids during expulsion and migration from source rocks

The aim of this work is to predict the viscosity of petroleum fluids in source rocks as well as in reservoirs. Indeed, petroleum migration is modeled through Darcyʹs law and requires knowledge of dynamic viscosity as a function of pressure, temperature and oil composition including asphaltenes. The method of experimental design is used to define 22 synthetic mixtures for determining the influence of composition on viscosity. The crudes are designed to represent liquids generated in source rocks of type II at different stages of maturation and of reservoir oils of the same origin. As this is a preliminary publication, experimental measurements have been carried out on eight synthetic crude oil mixtures so far. The study of crude oil viscosities requires, in the first place, an investigation of phase behaviour. In fact, seven mixtures precipitated asphaltenes. Precipitation of asphaltenes in source rocks might represent a new parameter in expulsion and migration modeling. Results show that the most determining factors on viscosity are the concentrations of the gas and of the heavy oil C15+ fraction. Perspectives are given for modeling the viscosity as a function of pressure, temperature and oil composition. The dependence on pressure and temperature is based on the published model of Kanti et al. (1989) and the mixing rule of Grunberg and Nissan (1949) is proposed to provide the variation in viscosity as a function of the oil composition. Further viscosity measurements are needed in order first to fit the model parameters, and later to validate the model results.