No abstract

An important aspect of efficient treatment of produced water is to promote the coalescence of dispersed oil drops. Therefore, a fundamental understanding of the relations between interfacial and physicochemical properties of crude oils and the coalescence process is essential, and elucidating these relationships was the aim of this investigation. Nine crude oils and fractions of two crude oils, where acids, bases, and asphaltenes were selectively extracted, were included in the studies. The dynamic interfacial tension and interfacial rheology of the oils were followed in synthetic produced water. The binary coalescence of oil drops was followed by a micropipette setup, and characteristic times for three phenomena occurring during the coalescence process were identified: the time of film thinning, the time for rupture of the thin film, and the apparent time of merger of the two drops. Decreasing the density of the crude oils and increasing the strength of the interfacial layer were determined to influence the coalescence process most significantly, by slowing it down. The elasticity and strength of the interfacial layers were primarily associated with the presence of asphaltenes at the interface. The strength of the interfacial layer decreased as the amount of aromatics and acidic components in the crude oil increased. In both cases, this was attributed to improved stability of the asphaltenes in the bulk of the crude oil.

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 waterÀcrude 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.

Electrical demulsification is considered an elegant method to enhance the separation of water-in-crude-oil emulsions. Understanding the mechanisms involved during this process remains a challenge for the further development of this separation method. The aim of this study is to elucidate the influence of the aggregation state of the asphaltenes on their conductivity, to determine the mechanisms governing conductivity in crude oils. Dielectric properties of two different asphaltenes extracted from crude oils (labeled CrA and CrB) and their solutions diluted in toluene or heptane were measured by frequency domain spectroscopy. When the heptane volume fraction increases, conductivity decreases. It also appears that the conductivity decreases with an increasing aggregate size. Conversely, decreasing the aggregate size increases the mobility of the charge carriers in the system and, consequently, increases the conductivity. On the basis of these observations, we propose here that the conductivity of asphaltenes is mostly governed by their mobility. The possible application of this method for determining the critical nanoaggregate concentration (CNAC) of asphaltenes is also evaluated and discussed.