Geoinformatika 2016; 2(58) : 38-42 (in Ukrainian)

DISPERSION OF ACOUSTIC WAVE BY PORES

V.P. Nagorniy, I.I. Denisyuk

Institute of Geophysics, NAS of Ukraine, 63G B. Khmelnytsky Str., Kyiv 01054, Ukraine, e-mail: vgv_nagornyi@ukr.net

Purpose. In order to intensify hydrocarbons recovery acoustic methods are used to impact oil and gas layers. Structural elements of the layers are pores filled with fluid. The purpose of the study is to reveal new possibilities to impact oil and gas layers by analyzing dispersion of acoustic waves, which appears during interaction of an incident pressure wave with pores.
Design/methodology/approach. We considered a flat acoustic wave propagation problem in a medium with spherical pore. A medium is characterized by density and velocity of longitudinal waves. A pore is filled with fluid or air. In the presence of pore during interaction of an incident pressure wave with pore, a dispersed wave appears in the medium. The wave field satisfies the boundary conditions of the wave field conjugation around and inside the pore. The problem has been solved in spherical coordinates. During the process of finding the solution of the problem we used the well-known Legendre polynomials, spherical Bessel functions, and spherical Hankel functions.
Findings. Sandstone was taken as an example of a medium with pores filled with fluid or air. We have discovered dependences of normalized amplitude of pressure waves around spherical pores of different radii in the directions of q = 0° and q = 180°. The character of the graphs indicates the resonance nature of an interaction of incident wave and pore. A dispersed wave appears when the size of a pore and the wavelength of an incident wave are commeasurable. Such pores display the properties of a resonance action.
Practical value/implications. It has been found that the presence of a resonance structure as pores in the medium of a layer increases the amplitude of pressure of an incident wave and raises the pressure amplitude of a pore incident wave, which results in the rise of the acoustic field level around it. The results obtained may be used in the process of developing new methods of acoustic action on oil and gas layers in order to yield gas growth in producing wells.

Keywords: amplitude, dissipation, fluid, geophysical medium, layer, pore, pressure, sandstone, wave.

The full text of papers

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