SU177641A1 - METHOD OF SEISMIC EXPLORATION - Google Patents

Description

The known methods of seismic prospecting using correlation techniques involve the use of multichannel seismic stations and the registration of oscillations at discrete points.

The proposed method allows to increase the accuracy of measurements and reduce the cost of field work due to the fact that the source of stationary mechanical vibrations is continuously moved along the profile, and the registration of vibrations is carried out by seismic receivers located at the ends of the profile.

The drawing shows a diagram illustrating the proposed method.

Seismic drums 1 and 2 are located at points A and B at the ends of the profile. The source 3 of continuous mechanical oscillations moves from L to B. It houses the receiver 4, which fixes the form of the excited oscillations. In the process of continuous movement of the source of oscillations from L to 5, records of seismic receivers are recorded at points A and B and installed at the source .;

On the fourth track, time stamps and distance marks are recorded. The processing of the obtained magnetograms is performed on a single-channel correlograph. At each point

the profile is supposed to receive records of the waves corresponding to nr A1ol u and to the counter locus.

For this, it is necessary to calculate the mutual correlation functions of records of seismmon receiver 1 m 4 2 and 4 on some interval of the profile D /.

Here, the correlator plays the role of an optimal filter that selects a signal of a certain shape, fixed by receiver 4, from the recording, registered by seismic receivers 1 and 2. Reflected and refracted waves, arising during the propagation of mechanical oscillator oscillations in the earth’s mass, are shifted for some time BUT/. The value of A is determined by the maximum value of the mutual correlation function.

Since several reflected or fixed waves are recorded on the recording, to separate them, it is necessary that the correlation functions of the useful signals are quickly attenuated over a short time interval. Since the correlator is an optimal filter, the useful output signals are recorded in a vnde sequential recording of pulses that are close in form to the autocorrelation function of oscillations excited by source 3 during the passage of interval A /. Thus, the main requirement for the source of continuous mechanical oscillations is the short duration of the autocorrelation function of the excited oscillations. It is known that zat-5 ..f. Autocorrelation functions have stationary random processes. The wider it is, the shorter the duration of the autocorrelation function.

By successively unshipping the interval A / 10 of the analyzed section under the profile, one can obtain a record of useful waves at any point between points A and B. By combining the starting points of all records, a multi-channel correlogram is obtained, similar to the usual seismogram recorded when elastic oscillations are excited at points A and B.

The application of the proposed method has the following advantages over the known modifications of the seismic exploration method.

1) When extracting useful waves, recording of oscillations excited in the A / profile interval is used. Since the source of the oscillations continuously moves along the profile, this is equivalent to continuous grouping in the interval A /.

When playing magnetograms, the duration of the analyzed part of the recording can be chosen arbitrarily, which makes it possible to carry out continuous grouping on any base. This is the most significant advantage of the proposed method .35

2) The depth of the method depends on the total energy of the oscillations excited in the interval A / analyzed section of the record. This energy is determined by the duration and intensity of oscillations of the generator 3. Me-40 n the speed of movement along the profile can control the total energy of oscillations per unit length of the profile over a wide range. Thus, the method allows using extremely simple means to carry out any accumulation of energy of the excited oscillations.

3) In the correlation analysis of the magnetograms, the recorded records are optimally filtered. Since the duration of the analyzed area is large (up to ten or more seconds), the bandwidth of the equivalent filter is very narrow and provides maximum suppression of various industrial noise and microseisms. To compensate for the frequency-dependent absorption of oscillations in the Earth’s depth, it may be useful to pre-filter the records of the receiver installed on generator 5.

4) The method makes it possible in principle to control the frequency spectrum of the excited oscillations, which makes it possible to concentrate the bulk of the energy of elastic oscillations in the desired frequency range.

5) Since there are only 2 receiving channels, it is easy to implement any grouping of seismic receivers in addition to the continuous grouping of excitation sources.

The use of low-channel (three-channel) recording equipment, no drilling costs and blasting operations provide high economic efficiency of the proposed method.

Subject invention

A seismic survey method based on the determination of the mutual correlation function of the process under study with harmonic oscillation, characterized in that, in order to improve measurement accuracy and reduce the cost of field work, the source of mechanical oscillations is continuously moved along the profile, and the oscillation detectors are located at the ends of the profile.

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