Molecular Thermodynamics of Asphaltene Precipitation in Reservoir Fluids

A pre®iously described molecular-thermodynamic framework, based on colloid theory, is used to correlate experimental asphaltene-precipitation data at high-temperature and pressure conditions. In this framework, asphaltenes and resins are represented by pseudopure components, and all other components in a crude oil are presented by a continuous medium that affects ®an der Waals attractions among asphaltene and resin molecules. Model parameters are e®aluated systematically from a®erage properties of asphaltenes and resins in crude oils, and from dispersion-force properties of the oil medium. Gi®en the composition of the medium, and asphaltene and resin concentrations, the molecular-thermodynamic model described here can be used to identify the onset of asphaltene precipitation, and the total amount of precipitation at the gi®en operation conditions. Calculated results for the effects of oil composition and pressure on asphaltene precipitation are in good agreement with at least some experimental measurements for four reser®oir fluids, including Texaco, Shell, Weyburn, and North-Sea crude oils.