Thermodynamics of Asphaltene Precipitation using the SAFT-VR Approach

摘要

The formation and deposition of asphalten-rich, solid-like material during oil recovery operations are well known in the industry. In the last few years, as the industry moves into more severe production conditions such as deep-water operations, tertiary oil recovery by gas injection and transport of oils with great differences in density and viscosity, the costs of maintenance, remediation and by lost production increases almost exponentially. Hence, a forecast of any possible problems are pertinent, and has stimulated the development of a great variety models to represent and to predict asphaltene precipitation from petroleum. Molecular-based theories have been used in the last decades to accurately describe the phase diagram of a wide variety of complex-fluid substances. Examples of these approaches are: the Perturbed Hard Chain Theory (PHCT), Simplified Perturbed Hard Chain Theory (SPHCT), the Perturbed Anisotropic Chain Theory (PACT), the Associating Perturbed Anisotropic Chain Theory (APACT) and the Statistical Associating Fluid Theory (SAFT). The main features of these approaches are that they introduce an accurate description of the thermodynamics of the system by modeling the intermolecular forces involved, and the parameters used have a molecular origin and are not state-dependent. As a consequence of these requirements, a molecular-based theory can be used to predict the thermodynamic behavior not only within the range of temperatures and densities where the parameters were correlated, but also to extrapolate the prediction for other values of density and temperature. Moreover, if all the intermolecular forces involved in reality are taken into account in the theoretical approach, which uses well defined state-independent molecular parameters, the theory then allows us to use standard combining and mixing rules in order to predict the mixing behavior using the molecular parameters values correlated for the pure components.