The ultrasonic waves effects on oil-water emulsification, coalescence, detachment, mobilization and viscosity in porous media
Ultrasonic wave technique is an unconventional EOR method, which has been of interest to researchers for more than six decades. Emulsification and demulsification are phenomena which occur at the interface of oil and water under the influence of ultrasonic waves. Therefore, the conditions in which emulsification becomes dominant over demulsification due to ultrasonic radiation in porous media should be further investigated. However, surfactants are the principal agents that enable oil and water to mix and are often the most expensive component in an emulsion. Therefore, selecting an appropriate surfactant formulation capable of mobilization of oil without significant surfactant loss due to adsorption and phase separation in the reservoir is very important. Estimation of solubilization parameters are great tools in designing economical emulsion flooding compositions. In this study, the effect of ultrasonic waves on the amount of oil and water solubilized by a unit of surfactant were investigated. It was observed that the emulsion volume and amount of oil solubilized in emulsion were increased by increasing salinity under short periods of ultrasonic wave radiation, and demulsification of the emulsion occurred after longer period of radiation. In addition, Hele-Shaw model tests were conducted to show microscopically the effect of long and short periods of ultrasonic waves’ radiation at the interface of paraffin oil and surfactant solution/brine. Diffusion of phases, formation of emulsion and gas bubbles were observed after short periods of ultrasonic waves’ radiation. However, demulsification and coalescence of surfactant solution/brine droplets inside emulsion was initiated after long periods of ultrasound radiation.Another objective of this study was to investigate directly the effect of ultrasonic waves on viscosity changes in three types of oil (paraffin oil, synthetic oil, and kerosene) and a brine sample. It was observed that the viscosity of all the liquids was decreased under the influence of ultrasonic waves in both uncontrolled and controlled temperature conditions. However, the reduction was found to be more significant for uncontrolled temperature condition cases. In addition, micro-model experiments were conducted to show other oil recovery mechanisms such as oil droplet coalescence, oil mobilization, and oil detachment from dead end pores under the influence of ultrasonic waves. The results revealed that these mechanisms happen in porous media under the influence of ultrasonic waves. Therefore, it was concluded that the use of ultrasonic waves could be suggested, not as a substitute for conventional EOR methods, but as an alternative or complimentary tool, which in certain instances may make conventional methods more effective and less costly.