Alterations of asphaltenes chemical structure due to carbon dioxide injection

Abstract

Asphaltenes precipitation during carbon dioxide injection to enhance recovery has been considered as one of the major challenges in the tertiary production phase. The effects of CO2 injection on asphaltenes chemical structure and stability in the matrix has not been fully understood yet. The present study aims to characterize asphaltenes structural alterations in the presence of CO2 at high temperature and pressure and then elaborates the mechanism in which these changes affect asphaltenes stability in the matrix. The chemical structure of four precipitated asphaltenes in the presence and absence of CO2 were characterized and compared. These results were coupled with the results of the stability assessment to determine the effects of structural alteration on asphaltenes stability in crude oil. Infrared (IR) spectroscopy results demonstrated the formation of amide functional group upon CO2 injection to the model oil. The precursor of such an observation is characterized to be the reaction of CO2 with amine functional group of the asphaltenes sample. Such a reaction led to the decrease of asphaltenes stability in the model oil sample. The results of the present study suggest that asphaltenes can be destabilized in the oil matrix through both chemical reactions and physical interactions. The presence of chemical functional groups that can react with CO2 in the reservoir conditions is the primary trigger to initiate asphaltenes destabilization. These findings can be used to further research asphaltenes disturbing mechanisms at the molecular level and scale them up to understand asphaltenes physical behaviors during CO2 injection.