SU1167558A1 - Method of seismic prospecting - Google Patents

Abstract

A METHOD OF SEISMIC EXPLORATION, including the excitation of elastic vibrations in the medium and recording them with seismic pickups located in the area under study for distances greater than or equal to the wavelength of elastic vibrations, and united in one recording channel, characterized in that, in order to increase the seismic intelligence due to the restoration of elastic waves with different apparent velocities, the signals of the seismic receivers amplify proportionally to the time of their propagation in the medium and enter them in time nye delay, distributed randomly .zakonu. with (l about ate 00

Description

This invention relates to seismic exploration methods for minerals in areas with complex environmental structures.

The purpose of the invention is to increase the efficiency of seismic prospecting by restoring elastic waves with different apparent velocities.

FIG. 1 shows a scheme for implementing the method; in fig. 2 is a diagram for combining the records of various receivers.

The method is implemented as follows.

Elastic vibrations are excited by source 1 and are received by a system of seismic receivers 2, the signals from which are sent to digital potentiometers 3, then to amplifiers 4, the outputs of amplifiers 4 are connected to delay blocks 5 of signals, the outputs of the latter are connected to a common link 6 7 seismic vibrations.

FIG. 2 shows the initial moments of the recordings of signals from different seismic receivers ti, tj, ta, .... tnb time-shifted relative to each other and summed in the same recording channel with different time delays.

A particular feature of seismic recording is the gradual attenuation of signals during the recording process, mainly due to a divergence proportional to time. Therefore, in the process of combining signals from different receivers with time shifts, signals of different amplitudes (from different receivers) are superimposed, which later makes it harder to extract weaker signals (signal-to-noise ratio decreases). To eliminate the effect of seismic wave divergence, the amplification of signals before their combination and delay increases. proportional to the time measured from the initial recording time ti. In this case, the recording of the first receiver tj starts from the moment to and has a predetermined duration. The recording of the next receiver begins at the same time and ends at the same time interval, but when combined into one channel, it is artificially shifted by the value of At tj-ti tj - О tj.

The total duration of the combined record is increased by the same amount.

Records of the remaining receivers are combined into one channel with different time delays (shifts) set in accordance with the Barker codes or sequences of type "no more than one match.

These sequences are used in communication technology to phase-modulate a carrier according to a random law in order to obtain the widest possible spectrum of the modulated signal and thereby transmit the maximum amount of information over the channel.

The combination of signals recorded by all receivers in the arrangement into one trass su gives a gain in the amount of recorded data

 .5tn

(one)

Р (i + a) 4t5И

where m is the number of receivers whose signals are combined into one channel; Д ta is the duration of the seismic process recorded by each receiver, and is the relative lengthening of the combined record equal to the maximum delay of the last of the combined signals divided by the duration of the record, i.e.

15

(2)

With m 24 and 5, the gain is more than ten times. In this seismic streamer contains only two wires, and the block

registration - one channel.

The source-induced elastic oscillations propagate in the medium along the rays 8 and are reflected at the boundary 9 and other deeper boundaries. Reflected

the signals are recorded by the arrangement of the seismic receivers 2. Further, the signals from the individual seismic receivers are amplified by digital potentiometers 3 and amplifiers 4 in proportion to the recording time and delayed in time in delay blocks 5 by intervals proportional to the values of the random sequence.

The need for digital potentiometers is due to the fact that when combined into one channel, voltages representing seismic signals must

have the same level along the time axis. Due to the same signal level, a better signal-to-noise ratio is provided when restoring tracks combined in one channel with different time shifts. At the same time, digital potentiometers provide high accuracy and stability of the conversion — amplification of signals in proportion to the recording time, which allows, if necessary, to return to true amplitudes in the process of signal processing with high accuracy. Amplification of signals in proportion to the recording time compensates for the divergence of seismic waves in the medium.

Placing digital potentiometers with preamplifiers and delay nodes not in the receivers (or close to them), but in the recording unit allows us to simplify the communication lines (up to a pair of ordinary wires) to the limit. This is especially important when areal registration of oscillations, when signals from 500-1000 and more receivers (groups of receivers) are simultaneously recorded. Under these conditions, it is possible, for example, to record the standard 48-channel seismic station signals from 48 t-groups of receivers, where m is the number of traces combined into one recording channel, practically

m 10-15. In this case, the composition of the main equipment will remain the same as for the profile observations, and the signals are recorded simultaneously at 480-720 points.

Claims (1)

METHOD OF SEISMIC EXPLORATION, including excitation of elastic vibrations in the medium and recording them by seismic detectors located along the studied area at distances greater than or equal to the wavelength of elastic vibrations, and combined into one recording channel, characterized in that, in order to increase the efficiency of seismic exploration due to restoration of waves of elastic vibrations with different apparent velocities, the signals of the geophones amplify in proportion to the time of their propagation in the medium and introduce temporary erzhki distributed randomly. Sd eat QO