Destabilization of water-in-crude oil emulsions using naphthenic acids

Naphthenic Acids (NAs) are widely believed to universally act in a stabilizing capacity during the formation of water-in-crude oil emulsions. This work provides evidence to the contrary wherein differences between commercially acquired NAs and those extracted from crude exhibit opposing effects on emulsion stability. Addition of the commercial NAs to a crude oil prior to water-in-oil emulsion formation resulted in an increase in emulsion destabilization rate. This was demonstrated via quantification of water droplet coalescence using pulsed field gradient nuclear magnetic resonance (NMR) and, over long timescales in the visual observation of the disengagement of a free water phase. The efficacy of the commercial NAs to act in such a demulsification capacity was shown to be effective at concentrations as low as 0.5v/v% and in the presence of saline water of up to 3.5 wt% NaCl. Differences in NA demulsifying ability was observed between three crude oils of various origins with some demonstrating clear visual phase separation whilst others remained in an emulsified state. Conversely, addition of NAs extracted from a crude oil at similar concentrations had negligible effect on the rate of emulsion destabilization. Comparative characterization of the commercial and indigenous NAs was performed using H-1 NMR, Diffusion Ordered Spectroscopy (DOSY), Rheometry, Pendant Drop Tensiometry, and Gas Chromatography-Mass Spectrometry. The results of this characterization indicated that differences in emulsion stability were governed not by differences in the reduction of emulsion droplet interfacial tension (IFT) but by the kinetics of molecular diffusion of the NAs during both the emulsification and destabilization phases.

Automated summary

Naphthenic Acids (NAs) are believed to stabilize water-in-crude oil emulsions, but this study found that commercial NAs have the opposite effect. Addition of commercial NAs to crude oil increased emulsion destabilization rate. However, NAs extracted from crude oil had negligible effect on emulsion stability. The differences in emulsion stability were attributed to the kinetics of NA diffusion during emulsification and destabilization.