Modeling of Asphaltene Onset Precipitation Conditions with Cubic Plus Association (CPA) and Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) Equations of State

Abstract

Asphaltene precipitation has been one of the major problems in the oil industry, and its modeling is still believed to be a quite complex issue due to the different characteristics of thousands of heavy components in crude oil. There have been several attempts to model asphaltene precipitation using various equations of state and empirical models. In the past few years, association models based on CPA and SAFT equations of state have been found to be promising models for studies of asphaltene precipitation. In this work, we compare asphaltene precipitation results obtained from different modeling approaches based on CPA, PC-SAFT with association (PC-SAFT (WA)), and PC-SAFT without association (PC-SAFT (WOA)) models. While the modeling approaches for the CPA and PC-SAFT (WOA) have been described before in various literature, the modeling approach for PC-SAFT (WA) is proposed in this work. All three models require the same number of experimental data points (at least three upper onset pressures and one bubble pressure) in order to obtain model parameters. Different types of asphaltene phase behavior for different reservoir fluids, where asphaltene solubility either decreases or increases with temperature, and where asphaltene precipitation occurs during reservoir fluid depressurization, and the effect of gas injection are studied in order to investigate thoroughly the potential and reliability of the models. A total of five reservoir fluids and one model oil are studied with all three models. It is found that the modeling approach with the CPA EoS is more reliable compared to the other two approaches used in this study. The advantage of the association term to describe interactions between asphaltene and other stock tank oil (STO) heavy components is also evident from this study. The sensitivity of SARA data to the modeling approach based on PC-SAFT (WOA) is also analyzed. Finally, the relationship between the binary interaction parameter of the asphaltene–CO 2 pair and crossover temperature, below which asphaltene solubility increases in reservoir fluid, with CO 2 gas injection is also studied.

Recent advances with association models for practical applications

“…Progress has been made also with asphaltenes (e.g. Arya et al [88]) and results are available with CPA, PC-SAFT and other SAFT variants [89,90]. We believe that explicit inclusion of the association is crucial for obtaining good results and we have shown that in a series of publications [e.g.…”

Modeling of Asphaltene Precipitation from Crude Oil with the Cubic Plus Association Equation of State

“…8 and 9) while approach-4 cannot. It should be noted that a similar approach based on the CPA EoS has already been studied with respect to the asphaltene precipitation onset conditions from the reservoir fluid in our previous studies [20][21][22].…”

“…Approach-1 is based on the CPA EoS and is the same approach as was proposed by Arya et al [20][21][22]. As shown in Table 1, the modeling approach-1 has a single component for the maltene fraction and six components for the asphaltene fraction.…”

The Phase Behavior of Heavy Oil and Propane Mixtures

“…Firoozabadi and coworkers (Kontogeorgis and Folas, 2009;Firoozabadi, 2010a, 2010b;Arya et al, 2015Arya et al, , 2016aArya et al, , 2016b Agrawal et al, (2012) introduced temperature-dependent binary interaction parameters to this model to predict the VL equilibria data at high temperatures. The interaction parameters between n-pentane and the bitumen pseudo-component were tuned to successfully model the saturation pressures and the VLL boundary region for these mixtures.…”