Abstract

Influence of Low Frequency Acoustic Field on Evaporation of Water Pellicles and Single Drops in Capillaries

A.Abrashkin, M.A.Raevsky (Institute of Applied Physics RAS, Nizhny Novgorod, Russia)

e-mail: abrash@hydro.appl.sci-nnov.ru

One of the factors reducing oil-containing layer permeability is the appearance of water films and even water drops (at the places of narrowing of pores) on the walls of pores. Water films reduce effective radius of a capillary and water drops block-up the movement of a liquid phase. In our report we've considered one of the ways low frequency acoustic waves influence the permeability of porous medium, connected with stimulating of the evaporation processes of water films and single props. We've analyzed the problem of systematic changing of a water film thickness in a cylindrical capillary with vibrating walls. It has been shown that in dependence on boundary conditions at the ends of a capillary (reflecting the degree of its connection with other capillaries inside porous medium) we can have monotonous reduction of water film thickness up to its complete disappearance. Physical possibility of this effect is connected to the non-linear character of the dependence of saturated steam pressure (above the curved surface of liquid) on its radius of curvature. Dynamics of the evaporation of a single drop under the influence of a low frequency acoustic field on the porous medium has been considered separately. It has been found out that in this case we also can have systematic reduction of a drop mass. We've got analytical expressions of the speed of the evaporation of pellicles and single drops under the influence of a longitudinal wave spreading along the axe of a straight cylindrical capillary. We have analyzed dependence of the effect on the radius of a capillary, saturated steam pressure, temperature and other parameters. It is important to mention that the suggested mechanism of the influence on the structures decreasing the mobility of oil has no limits that is it works even with smallest amplitudes of acoustic waves. It agrees with the results of natural experiments in low frequency acoustic stimulation of oil extraction.

Section : 6