Experimental application of ultrasound waves to improved oil recovery during waterflooding

Abstract

In oil reservoirs about 40% of the original oil in place is produced and the rest remains as residual oil after primary and secondary oil recovery due to geological and physical factors. Additional oil can be mobilized by applying some improved oil recovery methods. However, there is no universal IOR method to be implemented in any reservoir. Efforts are made to develop IOR methods with lower risk. One of these methods is the application of sound/ultrasound waves in the reservoirs to overcome the interfacial tension between oil and water, and reduce capillary pressure in the pores.In this study, laboratory experiments on core samples were conducted to investigate the ability of ultrasound waves to mobilize additional oil. The core flooding was performed horizontally and vertically and the wave stimulation was applied at original oil in place and at residual oil saturation after performing initial waterflooding. Oil/water relative permeability was calculated to evaluate the flooding performance in the presence and the absence of wave stimulation and the rate of oil recovery was determined. In addition, water fractional flow curves were considered to determine the average water saturation after breakthrough in the presence and the absence of ultrasound waves. Moreover, the effect of wave stimulation on unconsolidated core samples was investigated.Results show that the rate of oil displacement increases due to various identified mechanisms, and the interaction of the generated waves with the fluids in porous media causes changes in relative permeability and in water breakthrough. Wave stimulation at residual oil saturation was more effective than the case of original oil in place. Therefore, this method is advised to be used in depleted reservoirs. Moreover, wave stimulation on core sample with a compressive strength of <150psi (unconsolidated) is not recommended due to sand production.