Study of Dynamic Interfacial Tension for Demulsification of Crude Oil Emulsions

Abstract

Abstract Dynamic interfacial tension is one of several key factors relevant to the stability of crude oil emulsions. Studies of dynamic interfacial tension behavior associated with the demulsification of crude oil emulsions can have a great impact on the development of crude oil demulsification processes and products. This paper presents recent research on the interfacial behavior of interfaces between water, crude oil and several model oil systems, with and without added demulsifiers. The work involved use of drop volume tensiometer (DVT) measurements to reveal the correlation between demulsification effectiveness and interfacial elasticity. Demulsifiers which produced the most inelastic interfaces were generally found to break emulsions faster in field performance tests. Few studies have been published which directly relate actual field performance data to measurements of interfacial properties such as dynamic elasticity. In doing so this paper illustrates the relevance of this approach which could be useful for laboratory development of new products. Introduction Chemical demulsification of crude oil emulsions in petroleum production has proved to be a most economical and effective way to resolve well-known and sometime complicated emulsion problems. One of the challenging tasks we face today is to rationally and systematically develop high performance and cost effective demulsification products to meet the needs for crude oil production. A more scientific understanding of the mechanisms of demulsification of crude oil emulsions will have a great impact on the success of this task. Efforts to study the demulsification of crude emulsions have been described in a number of papers published in recent years.1,2,3 Although convincing results from these papers have shed light on the mechanisms of demulsification of water-in-oil emulsions, including revealing the factors that influence the stability of emulsions, to our knowledge there is no study published that directly relates actual field performance data to the measurable oil-water interfacial properties. One of purposes for rationalizing the relations between mechanisms and performance is to establish a concise and effective method to correlate field performance data with interfacial properties that can be measured and studied in the laboratory. This paper will report the results of this study. It has been known that chemical demulsification is a process in which chemical demulsifiers displace the emulsifying agents at the oil-water interface of emulsions, resulting in reductions in the stability of interfacial thin films and increased rates of film thinning. The overall effect of the process in water-in-oil crude oil emulsions is accelerated coalescence of water droplets. The demulsification process is a dynamic process that involves oil-water interfaces and emulsifying agents or emulsifiers that occupy at the interface and stabilize the crude emulsions. The emulsifiers could consist of a number of compounds, including alsphaltenes, natural surfactants, solids and organic acids. It is well known that there is no universal formula for crude emulsion treating due to the complex nature and variability of crude oil. Optimized treatment of emulsions is typically obtained through empirical testing the emulsion in question, and is affected by many factors including temperature, system geometries, etc. Recent studies on the correlation between demulsifier performance in water-in-oil crude emulsions and rheological properties of water/oil/water film have shown that low interfacial and film elasticity, high film diffusivity, high interfacial activity and low dynamic film tension all contribute to the good performance of demulsifiers.2,3However, these studies were based on the emulsions generated from crude oil and brine under laboratory conditions, and did not account for or reflect actual field performance, so the direct correlation to real field behavior was not established.