Molecular thermodynamics of asphaltene precipitation in reservoir fluids

A previously 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 an d resins are represented by pseudopure components, and all other components in a crude oil are presented by a continuous medium that affects van der W aals attractions among asphaltene and resin molecules. Model parameters are evaluated systematically from average properties of asphaltenes and resins in crude oils, and from dispersion-force properties of the oil medium. Giv en the composition of the medium, and asphaltene and resin concentrations, the molecular-thermodynamic model described here can be used to identify th e onset of asphaltene precipitation, and the total amount of precipitation at the given operation conditions. Calculated results for the effects of oi l composition and pressure on asphaltene precipitation are in good agreemen t with at least some experimental measurements for four reservoir fluids, i ncluding Texaco, Shell, Weyburn, and North-Sea crude oils.