Demulsification of crude oil emulsions tracked by pulsed field gradient NMR. Part II: Influence of chemical demulsifiers in external AC electric field

Abstract

Crude oil emulsions can reach stability levels that pose severe challenges for the processing industry. Certain conventional methods are used to deal with these challenges, such as chemical demulsification. In this article, two chemicals were mixed with crude oil emulsions to study their separation capabilities in the presence and absence of external AC fields. Experiments were conducted at 65 ⁰C to lower crude oil viscosity, which in turn affects separation efficiency. Effects from the chemical and electrical constituents on the crude oil emulsion was tracked by a pulsed field gradient NMR method, developed in a previous study. The NMR measured emulsified water content for 2 h, continuously, as a function of sample height. Given the water content, droplet sedimentation and free water layer kinetics could be quantified. Droplet size distributions from the top half oil phase were obtained at the beginning and end of each experiment, with the intent of mapping coalescence and sedimentation development of droplets. However, tracking droplet size evolution proved challenging due to rapid changes within the emulsion. The main focus with the NMR technique was therefore on sedimentation and free water layer kinetics. A synergy was observed between the two chemicals and low AC fields. The two chemicals showed varied degrees of separation efficiency, where limited amounts of water was resolved by chemical 1 without electric field, though it improved separation past the limit of electrical treatment when used in combination with AC field. Above a given electric field, sedimentation by electrocoalscence dominates, and the effect of chemical demulsifier is marginal. Chemical 2 achieved promising results as a lone separation method, while further enhancing separation in collaboration with AC fields.