Wax Precipitation from Reservoir Fluids: Modeling Solid-Fluid Equilibria in n-Alkanes Mixtures with two and Three-Parameter Equations of State

TASSIN, N.G.; S. B. RODRIGUEZ-REARTES; M.S. ZABALOY; M. CISMONDI

Porto Alegre

Congreso; CBTermo 2017 - IX Congresso Brasileiro de Termodinâmica Aplicada e V Escola de Termodinâmica; 2017

UFRGS

The deposition of waxes in reservoir fluids is the result of a supersaturation of the fluid, according to its composition and its conditions of temperature and pressure. To avoid this event it is required to know the phase equilibrium between the solid phase containing paraffins (n-alkanes typically in the C20-C50 range), and the fluid phases (liquid or gas). ImageTo model this phenomenon, an approach using an equation of state (EoS) to represent the fluid phases is used together with an additional expression (AE) for the fugacity of the precipitate n-alkane as a pure solid. According to a previously developed approach, the parameters of such AE (for the whole series of n-alkanes) were correlated, leading to good predictions of the melting curves of pure n-alkanes. Next, the predictions of solid-fluid (SF) and solid-fluid-fluid equilibria (SFF) were performed for binary systems composed of methane, ethane and propane with higher molecular weight n-alkanes. To achieve this, fluid phases were modeled using the Peng-Robinson (PR) equation of state, using an existing correlation for the values of the interaction parameters kij of the systems (and lij?s equal to zero). The previous results showed some deficiencies for the prediction of SF and SFF experimental equilibria in different systems. Those could be attributed, in principle, to an unsatisfactory representation of fluid-fluid equilibria by the PR-EoS. This work aims to study the ability of the selected modeling approach to reproduce, in particular, the experimental binary SFF equilibrium, and in general, the overall experimental phase behavior. RKPR EoS will be used to represent the behavior of the fluid phases. This equation has a pure compound parameter (δ1) of structural nature, additional to those of the classic EoS?s, and is expected to achieve better results in comparison to PR-EoS. New correlations are presented for the kij interaction parameter while linear mixing rules are used for the covolume with both models.