RU1798749C - Method of vibration seismic prospecting - Google Patents

Abstract

Usage: vibrational seismic by the method of reflected waves. SUMMARY OF THE INVENTION: A vibrating seismic signal is generated by a group of vibrators. The parameters of the control signals are selected taking into account the increased absorption of the high-frequency part of the cbun-signal by introducing an additional factor, the expression of which includes the absorption constants of the medium.

Description

The invention relates to vibro-seismic exploration by the method of reflected waves and can be used, in particular, in its shallow modification.

The essence of the invention lies in the fact that in the method of vibroseismic exploration, based on the simultaneous excitation by a group of vibrators of probing signals with lower fni and upper fBi cutoff frequencies and duration Ti, recording the total wave field and extracting seismograms from it by alternately correlating vibrograms with one of the probing probes signals and their subsequent interpretation, the durations of TI are determined from the expression.

t rsh, tt in m nab (fcpi - fcpl) Ti V 9 (fBi - fHi) 10 ----- - $: ---- v-t- AOG .U

where / o is the given noise immunity of the reception;

m is the logarithmic decrement of the absorption of seismic signals;

Tnab. - time of registration of the target reflecting horizon;

fni is the lowest frequency of the 1st vibrator;

fei - the highest frequency of the 1st vibrator;

r fni + fei

fcp.i -2-- average frequency of one

from vibrators;

fn1 H-fBI

fcp.i

.2

- the average frequency of the lowest frequency vibrator;

Aoi - the amplitude of the useful wave at the output of the seismic receiver when excited by the i-th vibrator;

p p - the rms interference level at the output of the seismic receiver.

The proposed method is based on the use of standard field systems using vibrational excitation sources. Using vibrators at the profile point, probing uncorrelated signals are simultaneously excited. AT

Yo

Yu

00

2

about

(1) the durations of the excited signals are as follows:

for the 1st signal Ti

for the 2nd signal T2

for the 3rd signal Tk

To compensate for attenuation of seismic signals at different frequencies, we determine the duration of the excited sweep signals in accordance with the equality

(1): .

for the 1st signal Ti

0.2 1 (20-20) x 10

twenty

for the 2nd signal T2

0.2 1 (60 - 20)

x 10

102 1 20

 5 s :.

102 1

60

twenty

for the 3rd signal Tk

0.2 1 (180 - 20) 20

g 4.2 s; 1Q2; 1,180

 x 10 22.1

If the duration of the excited sweep signals is too long, this value can be reduced by a factor of p due to an increase in the number of accumulations by the same amount. Thus, for the 3rd excitation, the excitation time can be reduced, for example, by 4 times. Then, time tz

22-1

-s- -5.5 s, but at the same time it is necessary

will provide the number of accumulations / 3 4. Thus, by using the proposed method, the dynamic range can be increased by 30 dB, and the resolution is 1.1-1.2 times.

Claims (1)

SUMMARY OF THE INVENTION A method of vibroseismic exploration based on the simultaneous excitation by a group of vibrators of probing signals with lower fi-n and upper fsi cutoff frequencies and duration П, recording the total wave field and extracting seismograms from it by alternately correlating vibrograms with one of the excited probing signals and their subsequent interpretation, characterized in that. which, in order to expand the dynamic range, increase the resolution while maintaining high productivity of the method, the duration of Ti is determined based on the expression P p: (& A0i2 (fBi-fHi) Yu m tna6 (fcpl fcpl) 20 5 0 5 0 where p is the noise immunity of the reception; gp is the logarithmic decrement of the absorption of seismic signals; 1nab is the time of registration of the target reflecting horizon; fHi-- lower frequency of the i-ro vibrator; fBi - the highest frequency of the 1st vibrator; fni + fei fcpr Ј of vibrators; ffn1 -f fBi fcpl --9 --- - the average frequency of one - the average frequency of the lowest frequency vibrator; Aoi - the amplitude of the useful wave at the output of the geophone when excited by the i-th vibrator; cr-rms interference level at the output of the geophone.