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

QUINZIO, MARTINA JULIETA; BENELLI, FEDERICO E.; RODRÍGUEZ REARTES, SABRINA BELÉN; CISMONDI DUARTE, MARTIN

Conferencia; PROSCIBA 2023: VI Iberoamerican Conference on Supercritical Fluids; 2023

Nitrogen (N2) is one of the most common non-hydrocarbon components of natural gas andoil. It is extensively used in oilfield operations for reservoir pressure maintenance, gascycling and gas lift. An increasing number of wells require pressure conservation to maintainproduction 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 severaladvantages, as nitrogen is abundant, economically easy to obtain and depending on injectionrate and pressure in the well, the cost of nitrogen may represent up to one quarter to one halfthe cost of natural gas.A thorough understanding of N2 - oil phase behaviour is essential for nitrogen applications inenhanced oil recovery; for example, the N2 - oil equilibrium phase diagram can be used toestablish miscibility and immiscibility conditions for the mixture.A correct and consistent description of the phase behaviour for these types ofmulti-component systems requires, in the first place, a good representation of the behaviourof the binary N2 - n-alkane constituent systems. In particular, those systems with a highdegree of asymmetry are more challenging to model.Predicting the phase behaviour of N2-containing systems with hydrocarbons is a challengingtask because all N2 - n-alkane binary mixtures develop, except with methane, type III phasediagrams according to the classification scheme of van Konynenburg and Scott. The type IIImixtures present two distinct critical curves, one starting at the critical point of thecomponent with the highest critical temperature and reaching to infinite pressures, andanother critical curve starting at the critical point of the component with the lowest criticaltemperature and meeting a three-phase liquid-liquid-vapour line at a higher temperature finalcritical point.In previous studies of the research group, the superiority of the generalisedRedlich-Kwong-Peng-Robinson equation of state (RKPR EoS) compared to the classicalPeng-Robinson (PR EoS) in predicting the vapour-liquid equilibrium (VLE) of binaryn-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 andvolume behaviour of N2 - n-alkane binary mixtures, including the most asymmetric ones, wedevelop in this work for PR and RKPR EoS new correlations of the attractive parameters kijwith temperature dependence for the homologous series of binary mixtures formed bynitrogen with normal alkanes. This also implies the parameterisation of pure nitrogenparameter for RKPR EoS (δ1), whereas for each n-alkane this structural parameter will betaken 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 phasebehaviour of N2 - n-alkane binary systems. RKPR EoS shows a superior performancecompared to PR EoS which is more noticeable in the case of more asymmetric systems.