Assessment of Asphaltene Stability in Crude Oils Using Conventional Techniques

Fundamental physicochemical factors involved in asphaltene precipitation under ambient conditions are studied in an effort to correlate them with the precipitation behavior observed in the oilfields. Asphaltene stabilization was evaluated by flocculation onset determination in titration experiments. The reversibility of asphaltene precipitation at ambient conditions was also explored with the proposed titration technique. It was found that the flocculation onsets of recombined long distillation residua are usually lower than the ones of the original samples.This finding suggests an irreversible nature of the process; this irreversibility is particularly observed for crude oils deemed stable from their field production records. Physicochemical characterization of crude oil hydrocarbon group-types was carried out and their influence on asphaltene stability was evaluated. Stable crude oils are characterized by possessing asphaltenes with lower density and lower aromaticity, compared with asphaltenes from unstable crude oils. Their resins show a higher stabilizing activity than the ones from unstable crude oils, and their maltenes also exhibit higher asphaltene stabilization effectiveness. Flocculation onsets of stable crude oils are higher than the flocculation onsets of unstable oils, at the same asphaltene content in the sample to be titrated. On the basis of this finding, a simple method is proposed for the evaluation of the possible risk of asphaltene precipitation in the oilfields.