SU1755230A1 - Seismic oscillation recording method - Google Patents

Abstract

Use: registration of seismic vibrations, multichannel digital seismic recording equipment. Summary of the Invention: Periodically, at intervals of time exceeding the seismic pulse duration, the amplitude spectrum of the seismic signal is measured. Find its upper frequency fmax. The cutoff frequency of the filter is determined to be equal to the sampling rate from the condition fg 4fmax. Then, the filter and sampling frequencies are consistently changed to the fbi values found. fgi and record the last or the corresponding sampling interval synchronously with the codes of simultaneously quantized signals. 2 Il.

Description

This invention relates to methods for recording vibrations during seismic exploration.

There is a method of digital registration in which signals are amplified and passed through a low-pass filter with a cut-off frequency fb, then sampled in time with a frequency of fg const, quantized in amplitude and recorded

The disadvantage of this method is the loss of information due to the fixed values of the sampling interval of the recorded signals.

The closest to the present invention is a method for recording seismic signals, which makes it possible to increase the information content by envisaging the registration of signals with an increase of 2-3 times against the usual sampling rate and subsequent sampling of samples with lower 4acTotaMH sampling during processing of seismograms on a computer. As a result, u get a few

time slices in different frequency ranges

The disadvantage of the method is the requirement of an increased memory size when registering signals, as well as disregarding the width of the spectrum of real seismic signals in the recording process.

The aim of the invention is to increase the resolution and efficiency of seismic exploration.

This goal is achieved by the fact that, according to the method of recording seismic vibrations, including the conversion of mechanical vibrations into electrical oscillations and their subsequent amplification, filtering and time sampling, set a priori maximum values of the sampling frequency of the signal fgo and the cut-off frequency of the filter fbo. The amplitude spectrum of the seismic signal is periodically measured at intervals of time longer than the duration of the seismic pulse, their upper frequency fmaxc is determined, determined by

with

The filter cut-off frequency values are from the equalizer and sampling frequencies of signals from the fgi 4fMaicc condition, then the filter and sampling frequencies are consistently changed to the set values and fgi and the latter is recorded synchronously with the codes of simultaneously quantized signals.

The considered method provides a more complete use of the spectrum of real seismic signals in the high-frequency region with the minimum amount of memory required to record all the information. The reduction of high frequencies in the spectrum of seismic vibrations provides an increase in the resolution and efficiency of seismic exploration in the study of complex and thin-layer media.

FIG. 1 shows a seismic receiver 1, an amplifier 2, a low-pass filter (LPF) 3, a signal sampling unit in time 4, an amplitude quantization unit 5. a recorder b, a spectrum meter 7, a spectrum analyzer 8, a sampling frequency pulse generator 9, a code generation unit sampling interval 10.

The method is implemented using the present device as follows.

Blocks 1-6 are connected in series as in a conventional digital seismic station and convert mechanical vibrations into electrical ones (with a seismic receiver 1), amplify them (with amplifier 2), filtering (LPF 3), sampling (sampling unit 4), amplitude quantization (quantization unit signals 5) and registration of signal codes (by recorder 6) To the output of amplifier 2, connected in series are meter 7 and spectra analyzer 8, sampling pulse generator 9 connected to sampler 4 and filter 3, and 7 measurer spectra and spectra analyzer 8 as well as with the recorder 6 through the block forming the sampling interval code 10.

Taking into account the additional blocks 7-10, registration is performed in this way.

Signals from the output of amplifier 2 enter the spectra analyzer 7, the output of which periodically, for example, 0.1-0.2 s, produces amplitude spectra of seismic signals entering the spectral analyzer unit 8, which determines the maximum amplitude spectrum A (f0) , find the frequency at which

COMPLETE CONDITION A (Tmzks) Kamzks) 0

To "1, and set the values of the Max generator

9 to form the sampling frequency of the signals in accordance with the equality fg 4fMatcc (with a continuous change in the frequency of the sampling pulses). With a stepwise change in the pulse sampling frequency, the frequency fg in the pulse generator 9 is compared with the frequency of this generator at the present time. If fg is below the operating frequency of the generator 9

0 and equal to or below its frequency (from a grid of predetermined sampling frequencies), then a lower sampling rate is enabled, and so on. The sampling rate pulses fg 4fM3Kc enter the sampler

5 4, which implements the discretization of signals with a frequency fg 4fM3Kc. At the same time, the frequency fMaKc is sent to the low-pass filter 3, in which the limit frequency fb fiHaxc is set. The same frequency synchronizes the operation of the meter and the spectrum analyzer. Pulses with a sampling frequency fg are fed to the input of block 10, which determines the code of the sampling interval and sends it to the recorder

5 The method is implemented by performing the following operations.

Excite in the medium elastic (mechanical) vibrations; register the vibrations coming to the surface and transform them

0 to electrical; set the maximum initial values of the sampling frequency fgo and the upper frequency of the filter fbo, perform frequency filtering and time variation oscillation with the parameters specified above; measuring the amplitude spectrum of the seismic signal at certain predetermined time intervals exceeding the duration of the signal; determine the maximum frequency of the amplitude spectrum of the signal f0i find the upper frequency T max of the amplitude spectrum of the signal from condition A (1 max) CAx v (f0): determine the new sampling frequency fgi from the condition fgi 4Gmax and the upper limit frequency of the filter from the fbt Gmax condition , change the sampling rate and filter for the values found fgi and Gy; Repeat the process in the following i-th time intervals.

0 An example of the invention is illustrated in the drawing shown in FIG. 2. Let us set the initial sampling frequency of seismic signals fgo 2000 Hz, which corresponds to the maximum frequency of the signal spectrum fg / 4 2000/4 500 Hz. At the same time, the amplitude spectrum of a real seismic signal, measured immediately after the start of the registration process, has a maximum of A (f0), for example, at a frequency of 200 Hz (figure 2). Accepted in the value of K 0.05

(the value of the amplitude of the spectrum is 5% of the maximum), we find (in FIG. 2) fiMaicc 450 Hz, which is slightly lower than the a priori given initial value of foMaKc 500 Hz. The sampling rate, corresponding to fiMaicc 450 Hz, is equal to

fgl e 4 Gyax 4-450 1800 Hz.

Accordingly, the limiting frequency of the low-pass filter fbi f 450 Hz. Thus, in the first seismic recording interval, when registering oscillations with an initial sampling frequency of fgo 2000 Hz, there is no loss of information. At the same time, it is possible to lower the upper frequency of the signal spectrum to f 1 max 450 Hz and the sampling frequency to fgi 1800 Hz.

The following measurement of the amplitude spectrum of the seismic signal, made, for example, 0.2 s after the first, gave a value of fnaKc of 250 Hz. Then fb 250 Hz, and the sampling rate will be fg2 4 fb 4-250 1000 Hz. Starting from this point in time, the sampling rate is set to fg2 1000 Hz, and the filter frequency fb 250 Hz. Then this whole process is periodically repeated at other times until the end of the oscillation registration process. The sampling rate at each time point is recorded on the seismic record.

The application of the proposed method provides a more complete use.

spectrum of seismic signals, and therefore, the recorded information corresponding to both small and medium and large depths, increasing in the final

Claims (1)

the result is seismic efficiency. Claims of Invention A method for recording seismic vibrations, including the conversion of mechanical vibrations into electrical oscillations. their subsequent amplification, filtering and discretization in time, while setting a priori the maximum values of the signal sampling frequency and the cut-off frequency of the filter fgo fbo. About t that which is. in order to increase the resolution and efficiency of seismic prospecting by more fully utilizing the high-frequency portions of the wave spectra reflected on various depths, the amplitude spectrum of the seismic signal is periodically measured at time intervals longer than the seismic pulse duration, their upper frequency is found, the values of the cutoff frequency of the filter are determined from the equality fbi fnaKci and the sampling frequency signals from the condition fgi 4fmax) then consistently change the filter and sampling frequencies to the set values fbi and fgi and record the latter synchronously with the codes of simultaneously quantized signals. FIG. CjЈ 0pfi # / rtt / t / W0