Development of a General Method for Modeling Asphaltene Stability

Asphaltenes constitute a potential problem in deep-water production because of their tendency to precipitate and deposit. A universal model to predict the stability of these species, under different conditions, is desirable to identify potential asphaltene problems. In our study, we present important advances in developing a general method to model asphaltene stability in oil. The perturbed chain-statistical associating fluid theory equation of state (PC-SAFT EoS), which has been previously validated, has been used to generate simulation data for a model oil containing different asphaltene precipitants. When dimensionless parameters are defined, the equilibrium curves of different multicomponent mixtures collapse onto one single curve. Universal plots for the bubble point and the onset of asphaltene precipitation have been obtained, which are in excellent agreement with results obtained from simulations. Extension of this model to mixtures containing dissolved gases, such as methane, CO2, and ethane, is also included. In the present work, we show a derivation of a new mixing rule for solubility parameters of mixtures containing liquids and dissolved gases. The agreement with simulation results and refractive index measurements is good. Results obtained in this work are very promising in providing new tools to model asphaltene stability under reservoir conditions.