Prediction of High-Pressure Phase Equilibria of Nitrogen + n‑Alkane Binary Mixtures with the RKPR EoS

QUINZIO, MARTINA JULIETA; BENELLI, FEDERICO; RODRIGUEZ REARTES, SABRINA BELÉN; CISMONDI, MARTÍN

Los Cocos, Córdoba, Argentina

Conferencia; VI Iberoamerican Conference on Supercritical Fluids (ProSCiba 2023); 2023

Universidad Nacional de Córdoba and Universidad Nacional del Sur

Nitrogen (N2) is one of the most common non-hydrocarbon components of natural gas and oil. It is extensively used in oilfield operations for reservoir pressure maintenance, gas cycling and gas lift. An increasing number of wells require pressure conservation to maintain production levels, which can be achieved by injecting natural gas, carbon dioxide or nitrogen. Nitrogen injection into oil reservoirs is an enhanced oil recovery technique that has several advantages, as nitrogen is abundant, economically easy to obtain and depending on injection rate and pressure in the well, the cost of nitrogen may represent up to one quarter to one half the cost of natural gas. A thorough understanding of N2 - oil phase behaviour is essential for nitrogen applications in enhanced oil recovery; for example, the N2 - oil equilibrium phase diagram can be used to establish miscibility and immiscibility conditions for the mixture.A correct and consistent description of the phase behaviour for these types of multi-component systems requires, in the first place, a good representation of the behaviour of the binary N2 - n-alkane constituent systems. In particular, those systems with a high degree of asymmetry are more challenging to model. Predicting the phase behaviour of N2-containing systems with hydrocarbons is a challenging task because all N2 - n-alkane binary mixtures develop, except with methane, type III phase diagrams according to the classification scheme of van Konynenburg and Scott. The type III mixtures present two distinct critical curves, one starting at the critical point of the component with the highest critical temperature and reaching to infinite pressures, and another critical curve starting at the critical point of the component with the lowest critical temperature and meeting a three-phase liquid-liquid-vapour line at a higher temperature final critical point. In previous studies of the research group, the superiority of the generalised Redlich-Kwong-Peng-Robinson equation of state (RKPR EoS) compared to the classical Peng-Robinson (PR EoS) in predicting the vapour-liquid equilibrium (VLE) of binary n-alkane - n-alkane systems, and then also for multicomponent mixtures, was demonstrated. The present work was conceived as a continuation of these previous studies.With the aim of proposing a model able to correctly and consistently describe the phase and volume behaviour of N2 - n-alkane binary mixtures, including the most asymmetric ones, we develop in this work for PR and RKPR EoS new correlations of the attractive parameters kij with temperature dependence for the homologous series of binary mixtures formed by nitrogen with normal alkanes. This also implies the parameterisation of pure nitrogen parameter for RKPR EoS (δ1), whereas for each n-alkane this structural parameter will be taken from a previous work in which a δ1 correlation for n-alkanes was optimized.The results show, for both PR and RKPR EoS, a very good predictive power for the phase behaviour of N2 - n-alkane binary systems. RKPR EoS shows a superior performance compared to PR EoS which is more noticeable in the case of more asymmetric systems.