SU195138A1 - METHOD OF SEISMIC EXPLORATION - Google Patents

Description

A seismic exploration method based on the use of vibrational sources of elastic vibrations (“Vibroseis) is known.

The present invention relates to seismic survey methods based on the use of vibrational sources of elastic vibrations.

In the known methods, the mutual correlation function of the process under study with harmonic oscillations is determined and, in addition, the source of mechanical oscillations is moved along the profile, and the oscillations are recorded at the ends of the profile.

However, at a uniform velocity of the vibrator, the attenuation of surface waves will still be insufficient, since at each point of the profile oscillations of different frequencies are excited, therefore, the usual grouping theory cannot be used to calculate the attenuation of regular seismic waves.

To improve the quality of seismic information according to the described method, oscillations of movement of the vibrator are continuously excited linearly for two cycles. In the first cycle, the vibrator is brought closer to the center of the displacement base, increasing the oscillation frequency, and in the second cycle, when the oscillation frequency decreases, the vibrator is removed by a distance equal to the partial from dividing the apparent speed of the suppressed wave by the double oscillation frequency. In addition, in order to exclude special devices for moving a vibrator with a variable speed, the vibrator is moved to separate profile intervals, within which the oscillation frequency changes to an optical magnitude.

In order to use conventional seismic vibrators to suppress waves with a known apparent speed, the entire vibrator oscillation range is divided into a number of bands with different mid frequencies and excite each frequency band at two discrete points located on different sides from the middle of the displacement base and removed first from it by a distance equal to the particular of dividing the apparent speed of the supplied wave by twice the frequency of oscillations excited at these points.

The described method is described in FIG. 1 and 2.

At excitation of oscillations of one frequency

in different points of the profile you can pick up

the distance between the points of excitation of AH in such a way that B and an opposite phase will come to the point of registration of the oscillations of the suppressed wave. Analytical relationship between distance AH apparent speed

NII f, in this case can be written as follows:

12/

As can be seen from this formula, when the frequency of the excited oscillations changes, it is necessary to change the distance between the points of excitation.

For this, the vibrator B (see Fig. 1) is moved from point A to point B. Kolebapi, excited by the vibrator, is recorded by multichannel placement of seismic receivers.

The vibrator starts working with generating and most low-frequency oscillations. In the process of changing the frequency of vibrations, and the sequential movement of the vibrator along the profile is produced. After the modulation cycle has been grinded at point B, the record of vibrator vibrations stops and it moves to point C. Then the vibrator moves from point C to point D with a linear change in the frequency of the generated oscillations from high to low frequencies.

To suppress a wave with a certain v, it is necessary for all frequencies to take AX -i

The ratio is - -. I like it 1 /

Since the variation of time / time obeys a linear law (the “Vibroseye” method), then it must vary backward proportionally t. Moving the vibrator at irreplaceable speed to satisfy the equality of the LA —controlled by certain technical difficulties, it is therefore proposed in the process flow of the vibrator to control the excitation and some frequencies in a predetermined profile interval.

The ratio between the band of generated frequencies and the length of the profile section should ensure the attenuation of the inhibited volga or any speed of the vibrator displacement (uniform or non-uniform) within this interval. It is obvious that the most iblagoi case corresponds to the excitation of oscillations at discrete points of the irofil. Therefore, we will estimate the distance between the discrete excitation points under the condition that the attenuation of all frequencies of the generated band should be no less than 10 times.

When oscillations are excited at discrete points, the entire diarazone of the frequency to be frequency generated must be divided into bands, the average frequencies of which differ, for example, by lOVo.

In the range of 20-100 Hz, it is necessary to move the vibrator to 15 discrete profile points in the process of generating one oscillation cycle.

In this case, the suppression of the surface wave will be sufficiently large, since the components of the extreme frequencies of each band of the generated oscillations are attenuated by 10 times (minimum value). Therefore, the general weakening of the will with a certain apparent speed can significantly increase this figure.

If we take into account the fact that the vibrator is moving along the profile in the process of exciting oscillations, then the band of frequencies that are operated on within one range and the same can be significant.

Subject invention

Claims (3)

1. The method of seismic exploration, based on the use of continuously moving vibration sources other oscillation and correlation extraction of useful signals, characterized in that, in order to improve the quality of seismic information, vibrator vibrations are excited and linear to the law two cycles, in the first cycle, the vibrator is approached, for example, to the center of the base and displacement, increasing the oscillation frequency, and in the second cycle, when the frequency of oscillations decreases, the vibrator and distance a rabbi to a part of the deletion of the apparent velocity of the pressure wave and a double oscillation frequency. 2. A method according to claim 1, characterized in that, in order to eliminate these devices In order to move the vibrator with a variable speed, the vibrator is moved at separate intervals on the irofil, within which a variation of the oscillation frequency occurs by a certain amount. 3. The method according to claim 1, characterized in that, in order to use conventional seismic vibrators to suppress waves with a known apparent speed, the entire vibration range of the vibrator is divided into a number of bands with different average frequencies and each frequency is excited in two discrete points located on a different side from the middle of the base of the non-displacement and removed from it to the distance equal to the particular by dividing the apparent speed of the suppressed wave by the doubled frequency of oscillations excited at these points. D C B A I 23 56789 W min L fmi Rig. fr. max gtr fmin min min FIG. 2