Thermodynamic Analysis of Asphaltene using SAFT EOS

to predict asphaltene deposition during carbon dioxide injection, the PC-SAFT statistical thermodynamic equation is used, assuming van der Waals forces predominate. All steps of the model work have been done using MATLAB coding software. In this study, according to Ghaim model, the solid phase of asphaltene is modeled as pure solid, which means that the heaviest compound (depending on the composition of fluid percentage C۲۵+ or C۳۲+) is divided into two parts, precipitable and non-precipitable, with all the same physical properties. Be. Considering that most of the reported percentage of oil has a heavy cut (Cn+) with less than ۳۲ (or ۲۵), so first it is necessary to splitting the heavy cut into single carbon groups and then lumping them into groups of several carbon numbers. The above two parameters, along with the two parameters of interaction of asphaltene with light and heavy alkanes (α and β), will form four adjustable parameters of the model. In order to reveal the effect of these parameters on the fugacity behavior of the precipitating compound in the liquid phase, it is necessary to analyze the sensitivity of the model to the values of the four parameters (fs, α, β, γ) we have paid. The results of the analysis show that with increasing the fourth and third parameters (γ and β), the order fs decreases and increases, respectively. But due to the wide range of changes, the impact is overwhelming. After determining this range using PSO search algorithm, with the aim of minimizing AAD error, the optimal values of these parameters are obtained according to the available laboratory data. Due to the fact that the interaction parameter of the precipitating compound with light alkanes should be larger than the heavy alkanes, so the PSO optimization algorithm has been modified so that the above constraint is maintained. In the flash calculations used in this dissertation to solve the Rockford-Rice equation, because Newton-Raphson method sometimes tends to diverge, the fmincon search function in MATLAB, which is proposed to solve constrained problems, is used. In order to allow the fmincon function to search accurately, the finite vapor molar fraction (V) is given as a constraint to the fmincon function as a negative arrow, instead of zero to one. Comparison of the results of PC-SAFT model with other models used for the studied laboratory data shows that PC-SAFT model, in addition to being more accurate than other models, this model can improve the process of sediment changes better than others. Predict methods Carbon dioxide gas, state equation.

کلیدواژه ها:

PSO optimization algorithm ، asphaltene deposition prediction ، injection CO۲ ، PC statistical thermodynamic injection PC- SAFT