Stable oil-in-water emulsions are very difficult to break and constitute one of the most difficult problems encountered during oil production. The emulsion viscosity is much higher than that of the segregated phases and, therefore, accounts of high pressure drop in the wellbore as well as low recovery in the reservoir. A laboratory investigation on the use of ultrasonic energy for enhancing the separation of suspended oil phase from aqueous media was carried out in this study.
This paper investigates the effect of ultrasonic energy on separation of oil and water from a stable oil-in-water emulsion. It was found that concentration of oil phase, composition of oil phase, ultrasonic intensity, and temperature are key factors in emulsion coalescence, which occurs after a relatively short time upon exposure to ultrasonic treatment. Also, clumping of oil droplets with higher oil phase compositions (10%, 35%), a possible explanation for reduced residual oil observed in past research efforts. Numerous microphotographs of the dynamic process of the coalescence were taken and changes in average droplet sizes noted. This led to the development of a mathematical model for the coalescence rate as a function of ultrasonic frequency, oil phase concentration, and other variables. These models are theoretically sound and easy to use. A comparison between mathematical model predictions and experimental results provided excellent agreement.
It was observed that, for the cases studied, ultrasonic treatment at the optimal energy level outperforms some chemical flocculants in terms of enhancing liquid-liquid separation. This technology could also be applied to postproduction emulsion separation as well as in situ wellbore treatment.
Oil-in-water emulsions are important in various phases of drilling, completion and production of petroleum wells. Oil-water emulsions are present whether it be in the oil reservoir itself or is formed as a result of the extraction process. These emulsions add considerably to the cost of transportation and refining and, in fact, to wellbore and reservoir problems.
Emulsions are conventionally thought of as an irreversible yet integral stage of oil production. The most important properties of these emulsions include particle size and distribution, viscosity, density, concentration, oil and carbon content, sound velocity, pH, zeta-potential, and surface charge, etc. Depending on the values of these parameters, emulsions can form or break. In most cases in petroleum engineering applications, however, these oilin- water emulsions need to be broken.
The breaking of emulsions, which is the demulsification process, involves the coalescence of small oil droplets to form larger ones. For accelerating the coalescence process for the enhancement of oil recovery, some additional forces are needed. There exists several techniques for enhancing demulsification. The typical ones found in the literature are the addition of chemical demulsifiers, pH adjustments, gravity or centrifugal settling, filtration, heat treatment and electrostatic demulsification1. The ultrasonic technique has the ability to rapidly break emulsions. This technique can actually be used to analyse emulsions non-destructively2.