Breaking of Water-in-Crude Oil Emulsions. 10. Experimental Evidence from a Quartz Crystal Resonator Sensor and an Oscillating Spinning Drop Interfacial Rheometer

Abstract

The presence of asphaltenes in crude oil is a key factor in stabilizing water-in-oil emulsions. Changes in asphaltene aggregation have a definite effect on the formation of an elastic and highly resistant film that stabilizes such emulsions. Herein, we report asphaltene aggregation changes using two different methods. First, with a quartz crystal resonator sensor, clear changes in the resonant parameters (Δfn and ΔΓn) of the quartz sensor fully immersed in a heavy crude oil + cyclohexane solution were observed when the asphaltene concentration in the solution reached approximately 1000 ppm. Second, using an oscillating spinning drop interfacial rheometer, a distinct discontinuity of the trend of the optimum formulation is found when the asphaltene content CA attains this threshold value. The formulation variation was obtained by two kinds of scans, which were shown to be equivalent: an increase in water salinity for an anionic surfactant-containing system and an ethylene oxide number (EON) decrease of a non-ionic surfactant. In both cases, the hydrophilic surfactant was used as a demulsifier in a fixed concentration CD. It is seen that the variation of the asphaltene concentration CA generates an unexpected sudden change at the interface, according to Winsor’s affinity ratio R and hydrophilic–lipophilic deviation (HLD) premises about the compensation of the effect of asphaltenes by a formulation variable change. These newly reported results happening around CA = 1000 ppm could help to further understand how the asphaltene aggregation models and the HLD equation can be tools for the formulator to find fast and efficient answers to crude oil dewatering.