SU851298A1 - Seismic prospecting method - Google Patents

Description

(54) METHOD OF SEISMIC EXPLORATION

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The invention relates to seismic exploration with vibrational sources of the excitation of elastic vibrations and can be used in the search and exploration of mineral deposits.

The known method of seismic prospecting consists in the excitation by a vibrator of a sequence of single frequency (monochromatic) signals with different durations, amplitudes and frequencies. After summing up all the recorded seismograms, before or after correlation, a vibroseis record is obtained that is equivalent to a record obtained from a vibrosignal with a predetermined spectrum of arbitrary shape 1.

The disadvantage of this method is the need to use several tens of single-frequency signals and, accordingly, the same number of switchings and equipment settings. This leads to low productivity of work, to unproductive consumption of magnetic tape and to rapid wear of the equipment.

A method of seismic exploration is also known, consisting in the excitation by vibrators of various narrow-band probing signals in frequency, the central frequencies of which are interconnected according to definite laws, and the signals themselves are modulated by a half-period of a sinusoid. After a separate recording of the seismograms and their summation, information is obtained that is equivalent to the information obtained from a vibrating signal with a predetermined spectrum 12.

Claims (2)

The disadvantages of this method. from low-performance due to the use of at least 7-10 narrowband signals, the need to use in serial equipment additional special hardware blocks that provide a sinusoidal curvature of narrowband signals, the complexity of the calculation and processing of the necessary series of narrowband signals and their envelopes over a given spectrum, the need in many cases for the attraction of this computer, the impossibility of using for the interpretation of seismograms or cuts obtained from separate links Rinse signals. because of their extremely low temporal and amplitude resolution. The purpose of the invention is to increase the efficiency of exploration by compensating for the energy loss of the oscillations. The goal is achieved by the fact that in the seismic survey method, which involves vibrating different frequency probing signals, separate recording and summing up seismograms from different signals, the excitation is carried out by separate groups of signals different from the signals of other groups in the frequency band position on the frequency axis, have equal for all groups rate of change of frequency in a fixed time interval, and summation is performed with time delays determined by cheni At (f, - - fo) / K where ti is the required delay; - rate of change of frequency; And minimum frequencies of signals, respectively, in each group and in all groups. The main difference from the proposed method from the known one is the use of several (usually 3-5), mainly broadband ones. probing signals interconnected only by an equal rate of change of frequency. Vibration excited in this way makes it possible to at least twice increase productivity, work and use serial equipment without additional equipment. The addition of registered oscillations with delays ut (f - f) / K makes it possible to significantly increase the speed of calculation of the required time shifts and ensures high performance of this operation. The method is carried out as follows. The drawing shows in advance the specified normalized amplitude spectrum Sp () and its approximation by the spectrum (f), consisting of several non-overlapping rectangles, but bordering on each other. Their number determines the number of groups of vibrational excitations t constituting the series. The vibration parameters for the group of cells are calculated from the basis of the amps & f and the sides of the P- corresponding rectangles, which together form the spectrum s (f). To do this, first calculate the rate of change of frequency K for the widest signal in the series (i.e. for a signal with a maximum uf. K b f, / T, where T is the selected duration of the probing signal. The value of K is the same for signals of all groups and determines the duration of all other signals T & f - K. Then the number of vibrations in each group is determined from the ratio n- (IJ. N) /, Z p., where N is the total number of vibrations in series. Next, vibrating vibrations are performed in each group with selected pairs oscillations belonging to each action group are recorded separately. Uncorrelated seismograms (vibrograms) included in a series are added with time delays for each group determined from the ratio & C (f - to) / 19 where f is the minimum frequency the signal of group i; tp is the minimum frequency of all signals (in series). Then, vibrograms are correlated in the usual way and time seismic sections are created using correlation corrections obtained as a result of correlation. This cut is close to the cut received with the signal. With a spectrum of So (f). With the correct specification of the spectrum) and its correct approximation, the time section is characterized by a higher quality than the similar section obtained using a signal having a rectangular spectrum. Parallel construction of seismic sections based on materials obtained by excitation with each individual signal, i.e. cuts for each group separately. In this case, it is possible to obtain new seismic information. The proposed method provides high-intelligence performance (since the spectral shapes that are usually required can be accurately approximated with three different types of signals in the case of their broadband) with sufficient accuracy for practical implementation; groups, the possibility of individual use in processing most of the signals / included in the series. As a result, the quality of seismic information is improved. Claims Investigation Method / Seismic Prospecting / Record in Excitation with Vibrators different frequency probing signals, separate recording and summation of seismograms from different signals, characterized in that, in order to assess the effectiveness of exploration by compensating for the loss of oscillation energy, the excitation is carried out by separate groups of signals that differ from the signals of other groups but having an equal for all rate of frequency change in a fixed time interval, and the summation is performed with time delays determined by the ratio; At; (f. -:) / K where ut; - claim delay; K is the rate of change of frequency; 5 f and - the minimum frequency of the signals, respectively, in each group and in All groups. Sources of information taken into account in the examination 1. US patent 3886493, cl. 340-15 5, published. 1975. 2. US patent 4004267 cl. 340-15,5, published. 1977 (prototype).