ASPHALTENE PHASE BEHAVIOR: EXPERIMENT AND MODELING USING THE SAFT EQUATION OF STATE

摘要

To investigate the effects of asphaltenes on reservoir oil phase behavior, the asphaltene instability boundaries and bubble point curves for a model "live" oil and a recombined oil were measured as functions of pressure, temperature, and gas concentration. The model "live" oil was a mixture of n-heptane-insoluble asphaltenes, toluene, and methane. The experimental data was then compared with predicted asphattene stability and bubble point boundaries calculated using a form of the Statistical Associating Fluid Theory (SAFT) equation of state. Due to the lack of conventional thermodynamic data, asphattene SAFT parameters were estimated from asphaltene-toluene-n-alkane mixtures refractive indices at the initial points of asphattene precipitation during n-alkane titrations. Comparison between model "live' oil measurements and SAFT predictions showed that SAFT-predicted asphattene instability and bubble point curves agree qualitatively with experimental data. Furthermore, both model "live" oil results and SAFT calculations showed that at constant temperature, when composition and/or densities were changed, asphattenes would be stable as long as the solution was above a certain solubility threshold, as indicated by the mixture refractive index or solubility parameter.