Role of Characterization in the Accuracy of PC-SAFT Equation of State Modeling of Asphaltenes Phase Behavior

The ability to capture asphaltene precipitation conditions is key to minimize costs associated with production caused by asphaltene depositing and blocking wellbores and pipelines. In this work, modeling of asphaltene precipitation of crude oils is performed using the perturbed chain form of the statistical associating fluid theory (PC-SAFT) equation of state (EoS). The characterization of choice is crucial to the accuracy obtained from any equation of state. Therefore, an alternative characterization is proposed where the molecular weight of asphaltenes is assumed to be temperature-dependent. This allows more flexibility in matching experimental data. Moreover, it compensates for deficiencies of near-infrared (NIR) spectroscopy and high-pressure microscopy (HPM) techniques used to measure asphaltene onset pressure (AOP). Results from six crude oils ranging from Middle East to Gulf of Mexico with varying gas injections are shown and compared. The proposed characterization shows some advantage over the original characterization especially in the lowerature region. Most importantly, it illustrates that better accuracy can be obtained without the need to consider association as proposed by some. In general, both characterizations give asphaltene precipitation tendency predictions within acceptable range of error. However, the modified characterization can be most beneficial when high accuracy is needed such as in calculating the amount of asphaltene anticipated to deposit.