Effect of formation water and its individual salts on the stability of water-in-heavy crude oil emulsions

Document Type : Research Paper

Authors

Federal University of Espirito Santo

Abstract

Petroleum emulsions are still considered a major challenge for the industry due to stability problems. Heavy oil contains high levels of polar compounds, and forms highly-stable emulsions that are difficult to treat. The aqueous phase of these emulsions, composed of formation water (FW), has high salinity and these salts can influence the behavior of the emulsions differently. Therefore, the main objective of this study was to evaluate the effect of different saline species on the stability of heavy-oil emulsions. The emulsions were prepared by adding increasing volumes of an aqueous phase containing deionized water (DW), FW, and saturated saline solutions. The emulsions were homogenized at 5,000 rpm for 3 min. The relevant factors were evaluated, including salt type, gravitational separation, temperature, droplet size distribution (DSD), and interfacial tension. The results revealed that emulsions prepared with some acid pH salts and high ionic strength showed kinetic instability with separation from 3.33 to 21.17% of the aqueous phase after 15–25 days of preparation, whereas the others remained stable after 30 days and even when submitted to heating up to 80°C. In relation to the average DSD, emulsions with acid pH salts showed higher values, whereas lower values were found in emulsions with DW. The interfacial tension of the dehydrated oil increased in the presence of the salts, especially those with acid pH and high ionic strength. Conversely, basic saline solutions decreased the interfacial tension considerably. These results can contribute to a fuller understanding of the stability of heavy oil W/O emulsions.

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