Asphaltene precipitation can severely hamper the petroleum extraction by plugging the pores or precipitation in production lines. Although the effect of temperature and pressure on asphaltene deposition is well known, how the variations in oil composition affect the asphaltene precipitation mechanism requires more clarity. This work investigates the effect of compositional changes on asphaltene stability. The impact of oil composition is explained by preparing pseudo-components by blending the crude oil with their own saturate fractions.
A systematic characterization of 11 different bitumen and crude oil samples is carried out on the basis of their density, viscosity, asphaltene content, and asphaltene composition. n-pentane is used to determine the asphaltene content of each sample by following a standard method. The asphaltene composition is then determined with Fourier Transform InfraRed (FTIR) spectroscopy. The asphaltene stability is tested by performing the onset asphaltene precipitation (OAP) tests.
The results from the characterization study indicated that there is no direct relationship between the asphaltene content and the density or the viscosity of the bulk samples. However, the FTIR profiles suggest that the polarity of the asphaltene molecules greatly influence the size of the precipitated clusters. The outcomes from the OAP tests were used to decipher the thermodynamic equilibrium state on the mechanism of asphaltene destabilization as per the change in the polar (resins and asphaltenes) to nonpolar (saturates and aromatics), saturates to aromatics, and resins to asphaltenes fraction of the bulk sample. It was observed that the increase in saturates concentration destabilized the asphaltene molecules and resulted in more precipitation. The presence of polar functional groups, as observed from the FTIR of the saturate fraction are believed to cause higher asphaltene precipitation.
During oil production, the temperature and pressure changes can lead to asphaltene deposition and alteration in the crude oil chemical composition. A holistic understanding of the thermodynamic equilibrium corresponding to these changes can be achieved by analyzing asphaltene destabilization or restabilization processes, specifically by changing the saturate concentrations. These results are extremely useful to comprehend the asphaltene stabilization mechanism and can improve the accuracy of existing asphaltene models.