Effect of existence state of asphaltenes on the asphaltenes-wax interaction in wax deposition

Abstract

Asphaltenes are the most elusive substances in waxy crude oil, especially the complex structures, which leads to significant precipitation and aggregation characteristics of asphaltenes, and affects the asphaltenes-wax interaction. In this study, the concept of the existence state of asphaltenes was introduced to semi-quantitatively investigate the precipitation and aggregation characteristics of asphaltenes. On this basis, the influence of the existence state of asphaltenes on wax deposition was studied by coldfinger device and high-temperature gas chromatography, and the composition and properties of the deposits were analyzed. Four main findings were made: (1) As the asphaltene concentration increases, the existence state of asphaltenes gradually transitions from dispersed state to aggregated state, and the asphaltene concentration of 0.30 wt% in this study is the starting point of the transition. (2) The existence state of asphaltenes in crude oil does affect the process of wax deposition, as shown in the fact that the dispersed asphaltenes promote the occurrence of wax deposition, while the aggregated asphaltenes can inhibit wax deposition. (3) In the presence of the aggregated asphaltenes, that is, when the asphaltene concentration is higher than 0.30 wt%, the shedding phenomenon of deposit layer was observed, and with the increase of aggregated asphaltenes, the deposit layer fell off earlier. (4) With the increase of the dispersed asphaltenes, the wax appearance temperature (WAT) and wax content of the deposits all showed an increasing trend, while with the appearance of the aggregated asphaltenes, the above situation was reversed. The findings of this study can help for better understanding of the interaction between the asphaltenes and wax in wax deposition.