Impact of the Composition and Content of Dissolved-State Paraffins in Model Oil on the Aggregation State of Asphaltenes and the Stability of Water-in-Model Oil Emulsion

Paraffins cause many issues during the production and transportation of crude oils. To date, there is abundant research on the rheological properties of crude oils after paraffin crystallization and the effect of precipitated wax particles on the stability of water-in-crude oil (w/o) emulsions. However, the impact of dissolved-state paraffins on w/o emulsion stability is insufficiently studied. This article focuses on the effect of dissolved-state paraffins with different carbon number distributions (CNDs) on the model oil/water interfacial characteristics and further the stability of water-in-model oil emulsions. It is found that the dissolved-state paraffins can affect the aggregation degree of asphaltenes, thus changing the w/o emulsion stability. The asphaltenes flocculate into larger aggregates when the paraffin content is increased to larger values. The aggregation weakens the diffusibility of the asphaltenes from bulk to interface; so, the diffusion rate is reduced significantly with the increasing paraffin content. The adsorption of larger-sized asphaltene aggregates can enhance the structural strength of the interfacial film, resulting in an increase of the interfacial dilational modulus. Consequently, the w/o emulsion stability is enhanced with the content increase of the dissolved-state paraffins in oil phase. The CND of the dissolved paraffins can also affect the stability of the water-in-model oil emulsions. The asphaltene aggregates in the model oil containing lower carbon number paraffins are smaller than those in the model oil containing higher carbon number paraffins. This suggests that the dissolved-state paraffins with a higher average molecular weight can better facilitate the aggregation of asphaltenes, consequently resulting in a more stable w/o emulsion.