Ultrasound technique is one of the unconventional enhanced oil recovery methods which has been of interest for more than six decades. However, the majority of the oil recovery mechanisms under ultrasound reported in the previous studies are theoretical. Emulsification is one of the mechanisms happening at the interface of oil and water in porous media under ultrasound. Oppositely, ultrasound is one of the techniques using in oil industry for demulsification of oil/water emulsion. Therefore, the conditions in which emulsification becomes dominant over demulsification under ultrasound should be more investigated. Duration of ultrasound radiation could be one of the factors affecting emulsification and demulsification processes. In this study a technique was developed to investigate the effect of long and short period of ultrasound radiation on emulsification and demulsification of paraffin oil and surfactant solution in porous media. For this purpose, the 2D glass Hele-shaw models were placed inside the ultrasonic bath under long and short period of radiation of ultrasound. A microscope was used above the model for microscopic studies on the interface of oil and water. Diffusion of phases and formation of emulsion were observed in both long and short period of application of ultrasound at the beginning of ultrasound radiation. However, by passing time, demulsification and coalescence of brine droplets inside emulsion was initiated in long period of ultrasound application. Therefore, it was concluded that emulsification could be one of the significant oil recovery mechanisms happening in porous media under short period of application of ultrasound.
Due to partial understanding of mechanisms involved in application of ultrasonic waves as enhanced oil recovery method, series of straight (normal), and ultrasonic stimulated water-flooding experiments were conducted on a long unconsolidated sand pack using ultrasonic transducers. Kerosene, vaseline, and SAE-10 (engine oil) were used as non-wet phase in the system. In addition, a series of fluid flow and temperature rise experiments were conducted using ultrasonic bath in order to enhance the understanding about contributing mechanisms. 3-16% increase in the recovery of water-flooding was observed. Emulsification, viscosity reduction, and cavitation were identified as contributing mechanisms. The findings of this study are expected to increase the insight to involving mechanisms which lead to improving the recovery of oil as a result of application of ultrasound waves.
Theoretically, Ultrasound method is an economical and environmentally friendly or "green" technology, which has been of interest for more than six decades for the purpose of enhancement of oil/heavy-oil production. However, in spite of many studies, questions about the effective mechanisms causing increase in oil recovery still existed. In addition, the majority of the mechanisms mentioned in the previous studies are theoretical or speculative. One of the changes that could be recognized in the fluid properties is viscosity reduction due to radiation of ultrasound waves. In this study, a technique was developed to investigate directly the effect of ultrasonic waves (different frequencies of 25, 40, 68 kHz and powers of 100, 250, 500 W) on viscosity changes of three types of oil (Paraffin oil, Synthetic oil, and Kerosene) and a Brine sample. The viscosity calculations in the smooth capillary tube were based on the mathematical models developed from the Poiseuille's equation. The experiments were carried out for uncontrolled and controlled temperature conditions. It was observed that the viscosity of all the liquids was decreased under ultrasound in all the experiments. This reduction was more significant for uncontrolled temperature condition cases. However, the reduction in viscosity under ultrasound was higher for lighter liquids compare to heavier ones. Pressure difference was diminished by decreasing in the fluid viscosity in all the cases which increases fluid flow ability, which in turn aids to higher oil recovery in enhanced oil recovery (EOR) operations. Higher ultrasound power showed higher liquid viscosity reduction in all the cases. Higher ultrasound frequency revealed higher and lower viscosity reduction for uncontrolled and controlled temperature condition experiments, respectively. In other words, the reduction in viscosity was inversely proportional to increasing the frequency in temperature controlled experiments. It was concluded that cavitation, heat generation, and viscosity reduction are three of the promising mechanisms causing increase in oil recovery under ultrasound.
CO2flooding process as a common enhanced oil recovery method may suffer from interface instability due to fingering and gravity override, therefore, in this study a method to improve the performance of CO2flooding through an integrated ultraosund-CO2flooding process is presented. Ultrasonic waves can deliver energy from a generator to oil and affect its properties such as internal energy and viscosity. Thus, a series of CO2flooding experiments in the presence of ultrasonic waves were performed for controlled and uncontrolled temperature conditions. Results indicate that oil recovery was improved by using ultrasound-assisted CO2flooding compared to conventional CO2flooding. However, the changes were more pronounced for uncontrolled temperature conditions of ultrasound-assisted CO2flooding. It was found that ultrasonic waves create a more stable interface between displacing and displaced fluids that could be due to the reductions in viscosity, capillary pressure and interfacial tension. In addition, higher CO2injection rates, increases the recovery factor in all the experiments which highlights the importance of injection rate as another factor on reduction of the fingering effects and improvement of the sweep efficiency.
An increase of nucleate pool boiling with the use of different fluid properties has received much attention. In particular, the presence of nanostructures in fluids to enhance boiling was given special consideration. This study compares the effects of graphene nanoplatelet (GNP), functionalized GNP with polyethylene glycol (PEG), and multiwalled carbon nanotube (CNT) nanofluids on the pool boiling heat transfer coefficient and the critical heat flux (CHF). Our findings showed that at the same concentration, CHF for functionalized GNP with PEG (GNP-PEG)/deionized water (DW) nanofluids was higher in comparison with GNP- and CNT-based nanofluids. The CHF of the GNP/DW nanofluids was also higher than that of CNT/DW nanofluids. The CHF of GNP-PEG was 72% greater than that of DW at the concentration of 0.1 wt %. There is good agreement between measured critical heat fluxes and the Kandlikar correlation. In addition, the current results proved that the GNP-PEG/DW nanofluids are highly stable over 3 months at a concentration of 0.1 wt %.
Many studies have investigated natural convection heat transfer from the outside surface of horizontal and vertical cylinders in both constant heat flux and temperature conditions. However, there are poor studies in natural convection from inclined cylinders. In this study, free convection heat transfer was examined experimentally from the outside surface of a cylinder for glycerol and water at various heat fluxes. The tests were performed at 10 different inclination angles of the cylinder, namely, φ = 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, and 90°, measured from the horizon. Our results indicated that the average Nusselt number reduces with the growth in the inclination of the cylinder to the horizon at the same heat flux, and the average Nusselt number enhanced with the growth in heat flux at the same angle. Also, the average Nusselt number of water is greater than that of glycerol. A new experimental model for predicting the average Nusselt number is suggested, which has a satisfactory accuracy for experimental data.
Ultrasound technique is an inexpensive and ecofriendly technology commonly used in oil and gas industry to improve oil recovery and its applications have been successfully tested in both laboratory and field scales. In this technique, high-power ultrasonic waves are utilized downhole to improve oil recovery and reduce formation damage in near wellbore region that causes a reduction in hydrocarbon production rate due to the penetration of mud, scale deposition, etc. In most of the cases, barriers for the oil flow to the wellbore are effectively removed by using the ultrasound technique and the effect of improved oil recovery may last up to several months. The aim of this paper is to provide an overview of recent laboratory, field and mathematical studies to serve as reference for future extensive examination of ultrasound assisted improved oil recovery. As an added value to this field of study, research gaps and opportunities based on the review of recent works were identified and factors that needs to be considered to improve the outcome of future studies were recommended.