HIGH PRESSURE SOLID-FLUID EQUILIBRIUM IN ASYMMETRIC SYSTEMS

S B. RODRIGUEZ-REARTES; M. CISMONDI; M.S. ZABALOY

Foz de Iguazú

Congreso; Primera Conferencia Iberoamericana de Fluidos Supercríticos (ProSCiba); 2007

Plapiqui

Solid precipitation is a frequent problem found in crude oil extraction, transportation, refining, etc. The ranges of interest for temperature, pressure and composition are necessarily wide, i.e., from extraction conditions to refining conditions. Such ranges are becoming increasingly wider due to the ever-increasing depths of the exploited reservoirs. This fact requires the availability of proper thermodynamic models for representing both, the fluid phase equilibria (FPE) and the solid-fluid equilibria (SFE), for oil-related systems, in wide ranges of pressure, temperature and composition. In the petroleum and gas industry, solid deposits can correspond to hydrates, asphaltenes and waxes.  In all cases, the systems are asymmetric. In this work, we concentrate on the simultaneous modelling of solid-fluid and fluid-fluid equilibria for binary synthetic systems, i.e., light n-alkane / heavy n-alkane  systems, over a wide pressure range, which  are of relevance to the wax precipitation problem. The model for the fluid phases is of the equation of state type. We observed that an optimum fit of the experimental FPE data does not guarantee a good enough description of the SFE. For studying the FPE, we used the latest version of our in-house computer program GPEC: Global Phase Equilibrium Calculations. We performed SFE calculations by generating complete solid-fluid equilibrium regions, each one in a single run. The calculation technique is similar to the one adopted in GPEC for FPE regions.