Wax precipitation from Reservoir fluids: Modeling solid-fluid equilibria in n-alkanes mixtures with two and three-parameter equations of state

TASSIN, N.G.; BELÉN RODRIGUEZ REARTES; ZABALOY, MARCELO S.; CISMONDI, MARTÍN

Porto Alegre

Congreso; IX Congresso Brasileiro de Termodinámica Aplicada (CBTermo 2017); 2017

Thedeposition of waxes in reservoir fluids is the result of a supersaturation ofthe fluid, according to its composition and its conditions of temperature andpressure. To avoid this event it is required to know the phase equilibrium betweenthe solid phase containing paraffins (n-alkanes typically in the C20-C50range), and the fluid phases (liquid or gas).Tomodel this phenomenon, an approach using an equation of state (EoS) torepresent 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 apreviously developed approach, the parameters of such AE (for the whole seriesof n-alkanes) were correlated, leading to good predictions of the melting curvesof pure n-alkanes. Next, the predictions of solid-fluid (SF) andsolid-fluid-fluid equilibria (SFF) were performed for binary systems composedof methane, ethane and propane with higher molecular weight n-alkanes. Toachieve this, fluid phases were modeled using the Peng-Robinson (PR) equationof state, using an existing correlation for the values of the interactionparameters kij of the systems (and lij?s equal to zero). The previous resultsshowed some deficiencies for the prediction of SF and SFF experimental equilibriain different systems. Those could be attributed, in principle, to anunsatisfactory representation of fluid-fluid equilibria by the PR-EoS. This work aims to study the ability of the selected modelingapproach to reproduce, in particular, the experimental binary SFF equilibrium,and in general, the overall experimental phase behavior. RKPR EoS will be usedto represent the behavior of the fluid phases. This equation has a purecompound parameter (δ1) of structural nature, additional to those of theclassic EoS?s, and is expected to achieve better results in comparison to PR-EoS.New correlations are presented for the kij interaction parameter while linearmixing rules are used for the covolume with both models.