Enhancement of Liquid Flow Through a Porous Medium by Ultrasonic Radiation

A new method to enhance the oil production rate is irradiation of the near-wellbore region by an ultrasonic source. The limited success for the application of ultrasound in well stimulation to date, however, is due to the lack of understanding of the physical mechanisms between an acoustic wave field and a porous medium. In this paper the mechanism in which ultrasonic radiation deforms the walls of the pores in the shape of traveling transversal waves is studied. A quantitative description of the mechanism indicates that these waves induce a net flow of the liquid inside the pores, identical to peristaltic transport. Numerical calculations show a damping effect of liquid compressibility and a strong influence of pore wall hardness and power output on the net flow rate induced. The occurrence of a flow induced by ultrasound has been confirmed by laboratory experiments. In these experiments a water velocity of almost 1 cm/s through a rubber capillary of 0.15 mm radius could be induced by an ultrasonic source of frequency of 20 kHz. By a comparison between the trends observed in the experiments and the theoretically predicted trends, the role of the peristaltic transport mechanism in acoustic well stimulation is discussed.