Enhanced Sedimentation and Coalescence by Chemicals on Real Crude Oil Systems

Water-in-oil emulsions of a crude oil were prepared and destabilized by addition of demulsifiers. The goal of the study was to compare two different techniques used to evaluate demulsification effectiveness and to study the interfacial response of the demulsifiers. The stability of these emulsions was determined in an E-Crit cell and low-field NMR, and the interfacial response of the demulsifiers was measured with the oscillating pendant drop method. The E-Crit cell measures the electric field required to induce the formation of free water and the NMR monitors the vertical movement of dispersed water droplets. The stability measurements and the interfacial response gave different indications on the demulsifier effectiveness at different demulsifier concentrations. The difference could be attributed to the difference between how the stability is measured or by the effect of the electric field on the demulsifiers. The separation profiles obtained in the NMR illustrated that the demulsifiers increase the sedimentation velocity at increasing demulsifier concentration. The water recovery rates indicated that the demulsifiers had different properties. The interfacial study showed that low concentrations of demulsifiers decrease both the elastic and viscous modulus of water-crude oil interface. At higher dosages both moduli increase. The different trends can be explained by considering the ratio between the total interfacial area and the demulsifier dosage. The demulsifier dosage was kept similar, but the amount of available area varied from the emulsion stability measurements and the interfacial study.