Geoinformatika 2019; 2(70) : 58-64

УДК 550.832+550.8.05

SIMULATION OF WAVE FIELD IN MEDIA WITH DIFFERENT ASPECT RATIO AND ORIENTATION OF VOIDS

V.V. Khalimendik

Kyiv National University of Taras Shevchenko, Institute of Geology, 90 Vasylkivska str., Kyiv, 03022, Ukraine, e-mail: valeriikhalimendik@gmail.com

Purpose. This paper describes a study of the results of acoustic 2D modeling to determine the influence of the shape and orientation of the pores on the acoustic properties of the rock. The aim of this work is to study the influence of the shape and orientation of pores on the acoustic properties of the rock, according to the results of 2D acoustic modeling by full-wave method in the software package «Tesseral».

Design/methodology/approach. For implement the simulation procedure in the software package «Tesseral», the model dimension was scaled so that the voids of 0,1 mm occupied one cell of the 1×1 m grid, that is, increased by 10⁴times. The frequency of the acoustic signal was reduced by the same number of times. The total size of the model corresponds to the size of the acoustic probe — 2×1 m. The calculation results for several models of Sandstone with a homogeneous composition of voids filled with water are presented. One model is isotropic and filled by disks with a diameter of 1 mm, the other two anisotropic — cracks with a diameter of 1 mm and a length of 10 mm are oriented along and across the wave motion. The rest, also anisotropic, filled with different variations which depending on the ratio of the axes of the ellipsoid and the orientation in space.

Findings. The result of 2D modeling shows that different not only the shape but also the orientation of voids in the matrix of the geological environment have different effects on its acoustic properties. Especially noticeable is the difference between the voids with round shape and elongated in the direction of the wave.
With increasing crack length, if it is stretched along the direction of the wave, the velocity of acoustic waves is significantly reduced. In cases where the cracks are stretched across the direction of the wave, the velocity of acousticwaves practically does not change, varies in the range of ±100 m/s.

Implications. For the first time, the method of numerical solution of the problem of full wave modeling by the finite difference method was applied to study the influence of different types of voids and their orientation in space, in a model close to the real borehole environment. The disadvantage of the above modeling method is the time spent on the calculation of one model — about 50—65 hours. This is due to the great detail (small grid step). There are two ways to reduce the time spent on the calculation: use more powerful computing resources such as a graphics card or processor, or reduce the discretization of the grid.

Keywords: acoustic properties, different types of pores, pore aspect ratio, rock porosity, sonic well log, sonic wave simulation, elastic modeling.

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Received 26/02/19