PREDICTION OF ASPHALTENE INSTABILITY UNDER PRESSURE DEPLETION AND GASINJECTION WITH THE SAFT EQUATION OF STATE

摘要

The Statistical Association Fluid Theory (SAFT) equation of state (EOS) with a perturbed chain dispersionterm (PC-SAFT) is used to predict the asphaltene phase behavior in a model oil (mixture of asphaltene,toluene and methane) and in a recombined oil when pressure declines in an oil reservoir and under theinjection of carbon dioxide (CO2), nitrogen (N2) and normal alkanes as precipitants. The pure componentPC-SAFT parameters were obtained from the literature and the oil/gas pseudo-components were estimatedfrom molecular weight correlations. For asphaltene, the parameters were tuned to meet the experimentalasphaltene precipitation onset of the reservoir fluid at wellbore conditions. SAFT-predicted asphaltenestability and bubble point curves agree qualitatively with experimental data reported in the literature.Destabilization of asphaltenes with CO2 occurs at about 50 mole%. N2 produces a high asphaltenedestabilization effect even at low concentrations. The SAFT model was found to be in qualitativeagreement with experimental data for the precipitant/crude oil systems in this study.