The Asphaltene and Wax Deposition Envelopes

ABSTRACT Asphaltene and wax phase behavior is quite different than the conventional “PVT” phase behavior. Asphaltenes exhibit a behavior at some thermodynamic states called flocculation. That is, asphaltene particles or micelles aggregate or flocculate into larger aggregates or flocs. The locus of all thermodynamic points in a P-T-x phase diagram at which flocculation occurs is called the Asphaltene Deposition Envelope (ADE). Paraffin waxes, on the other hand, at some thermodynamic states, exhibit the phenomenon of crystallization. The locus of all thermodynamic points in a P-T-x phase diagram at which wax crystallization occurs is called the Wax Deposition Envelope (WDE). Asphaltene flocculation can be both reversible and irreversible (as expected from the asphaltene colloidal nature). Wax crystallization is generally a reversible process. However, paraffin waxes more than often precipitate together with resins and asphaltenes (which are said to be responsible for the observed irreversible thermodynamic ...