Ultrasonic based methods to characterize stability of water-in-crude oil emulsions

Emulsion technology are heavily use in many major chemical industry from pharmaceutical industry to those involving crude oil production and refining. In particular, water-in-oil emulsions present a big challenge to industrial operations. Generally, crude oils are characterized by high salt levels, which can cause several problems, including catalyst poisoning and heat exchanger fouling. Different techniques have been adopted to separate oil-water emulsions into their individual phases. However, the separation process is influenced by several factors, such as crude oil composition and the distribution of the droplet sizes, which must be addressed to achieve a more efficient separation process. Different analytical techniques like optical and electron microscopy have been developed to characterize the droplets into emulsions. However, most of these methods are only suitable for dilute applications, which is not the case with emulsions in industrial settings that are concentrated and optically opaque. Additionally, a few techniques that have exhibited promising applications, such as nuclear magnetic resonance (NMR), are quite expensive and practically limited.

Recently, ultrasonic attenuation spectroscopy (UAS) has been identified as a promising technique for measuring the distribution of droplet size in emulsions owing to its ability to characterize optically opaque and concentrated emulsions effectively. The working principle of the UAS technique is based on converting the ultrasound measurements into emulsion stability and droplet size variations. It is worth noting that despite the wide range of the ultrasonic wave frequency, frequencies below 20MHz are preferred for industrial applications in different fields. However, an increase in the ultrasonic frequency results in a corresponding decrease in the attenuating of the propagating wave. Thus, careful frequency selection is necessary to maintain the desired signal-to-noise ratio.

In a new study by conducted by The University of Western Ontario scientists, Mr. Embark Alshaafi and Dr. Anand Prakash together with Mr. S.M. Mercer from Imperial – Sarnia Technology Applications & Research, developed new ultrasonic-based method to monitor and characterize the stability of water-in-crude oil emulsions. Considering the possible differences in the acoustic signals derived from water, oil and emulsion phases, the ultrasonic techniques were equipped with the necessary qualities for effective system monitoring. Their research work is currently published in the journal, Colloids and Surfaces A: Physicochemical and Engineering Aspects.

In their approach, the emulsions were prepared in crude oil and mineral samples of different types to characterize the effects of various acoustic variables on the basis of their variation and stability in droplet size distribution. The structure of the emulsion droplet and its stability were examined via optical spectroscopy and separation of water phase with time, respectively. An ultrasonic prole was used to track the changes.

The research team demonstrated the feasibility of the proposed ultrasonic method to characterize and analyze crude oil emulsions with different asphaltene content to prevent the formation of very stable emulsions. Parameters monitored included the changes in the acoustic velocity, frequency spectrum and signal attenuation of the propagating wave. An increase in the emulsion attenuation of a particular oil sample indicated fine droplet distribution, further improving the emulsion stability. Additionally, the attenuation data analysis suggested the dominance of rheological related factors. Notably, the separation process was non-destructive with minimal invasion. This, together with the hardware compactness in real-time, robust and reliable results.

In summary, the study investigated the feasibility of ultrasonic-based methods to monitor emulsion stability and track changes in the emulsion characteristics. For the first time, this method was applied to determine the asphaltene content levels in crude oil to suppress emulsion stability. The technique successfully distinguished the effects of different factors on emulsion compost and stability with simultaneous acoustic velocity and attenuation measurements. Compared to the separated water volume measurements, attenuation measurements provided a thorough understanding of the separation process and the observed attenuation-induced effects. In a statement to Advances in Engineering, Dr. Anand Prakash explained the study findings would pave the way for industrial application of ultrasonic-based methods, especially crude oil extraction and refining.