Study of the Cation and Salinity Effect on Electrocoalescence of Water/Crude Oil Emulsions

Abstract

The resolution of water-in-crude oil (W/O) emulsions formed during extraction or desalinaton processes of crude oil is still a problem for the oil industry. Among the main separation processes used today, electrostatic separation induced by the application of DC or AC electric fields is the most interesting because it is ecologically correct. However, the electroseparation efficiency is still limited by the current lack of knowledge concerning the mechanism that is behind this process. Stabilization of the water/crude oil emulsion is guaranteed, mainly, by resins and asphaltenes that are present at the W/O interface, forming a rigid cross-linked film that wraps the droplets. The influence of salts and the salinity of the aqueous phase on the stability of emulsions is poorly known because most researchers use, as the aqueous phase, a complex saline solution composed of a mixture of chlorides and sulfates of mono- and divalent cations to simulate the composition of seawater. Thus, the isolated effect of each type of cation may not be known. In this work, we used the rheology technique to study the effect of cation type and salinity of the aqueous phase on the stability of water/oil emulsions, under application of a DC electric field. It was verified that the stability of the emulsions follow this order: H2O ≪ Na+ ∼ K+ < Ba2+. It was also observed that the presence of salts increases the stability of the emulsions up to a critical value of ionic strength (∼0.1–0.3 mol L–1, depending on the system), above which the stability decreases, tending to that observed for the emulsion produced with water.

Demulsification techniques of water-in-oil and oil-in-water emulsions in petroleum industry

“…Perles and colleagues [71] applied the rheology method and explained this contrast by concluding that the presence of salt improves W/O emulsion stability up to a critical ionic strength value (~ 0.1-0.3 mol L -1 ) above which its stability is diminished. On the other hand, electro-rheological investigations proved that W/O emulsions with water phase containing divalent cation (Ca 2+ or Ba 2+ ) are more stable than those with aqueous phase composed of monovalent cation (Na + or K + ) [70,71].…”

“…Perles and colleagues [71] applied the rheology method and explained this contrast by concluding that the presence of salt improves W/O emulsion stability up to a critical ionic strength value (~ 0.1-0.3 mol L -1 ) above which its stability is diminished. On the other hand, electro-rheological investigations proved that W/O emulsions with water phase containing divalent cation (Ca 2+ or Ba 2+ ) are more stable than those with aqueous phase composed of monovalent cation (Na + or K + ) [70,71]. On the contrary, the presence of salts with divalent cation raises demulsification competence of O/W emulsion to a greater extent than that with monovalent cation, which is probably assigned to the lesser hydrophilicity of the former [3,14,72].…”

“…Electrical demulsification is generally considered advantageous from the perspective of energy consumption as compared with other demulsification approaches, such as heating or centrifugation, in addition to ecological validity [71,216]. However, the drawback of this process is formation of fine secondary droplets during the coalescence, making it more burdensome to separate the produced smaller water drops.…”

Crude Oil/Brine Interactions and Spontaneous Formation of Micro-Dispersions in Low Salinity Water Injection

“…Moreover, in terms of emulsion droplet size, it was observed that significant reduction in emulsion sizes take place at lower salinities (Moradi et al 2011). They also demonstrated that the stability of the emulsions formed in an aqueous environment saturated with divalent ions (Ca ++ ) differs from monovalent (Na + ) systems (Wang andAlvarado 2012 andPerles et al 2012). However, it should be pointed out that they deliberately agitated oil and brine to form the emulsions whereas in our case, the observed microdispersions form spontaneously when a crude oil contacts low salinity brines.…”

An Overview of Recent Advances in State-of-the-Art Techniques in the Demulsification of Crude Oil Emulsions

“…However, this hardware has considerable volume as well as expensive to install on offshore platforms [155]. Electrical demulsification is generally considered advantageous from the perspective of energy consumption as compared with other demulsification approaches, such as heating or centrifugation, in addition to ecological validity [156,157]. However, the drawback of this process is the formation of fine secondary droplets during the coalescence, making it more burdensome to separate the produced smaller water drops [158].…”