SU1749860A1 - Method of seismic prospecting - Google Patents

Abstract

The invention relates to seismic exploration and can be used for prospecting and exploration of oil, gas and ore deposits in field studies using the vibroseis method. The purpose of the invention is to increase the resolution of seismic exploration. In the method, a series of sequences of seismic oscillations is excited, the source control signal for each of which is formed from the period of the original signal, the received seismic signals are correlated with a reference signal consisting of an integer number of periods. The resulting correlograms summarize, and the period of each of the control signals of the seismic source is formed from single-polarized single oscillatory pulses with the following law, which is established such that the periodic autocorrelation function of the original signal is zero over a period. The time intervals at which single oscillatory pulses are excited are set equal to the time interval of a single excitation skip, and the oscillation frequency in single vibrational pulses in different sequences of a series is different. 1 hp f-ly, 1 ill. (Ls

Description

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The invention relates to the field of seismic exploration and can be used for prospecting and exploration of oil, gas and ore deposits during field studies by the vibration seismic method.

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

The drawing schematically shows the series and structure of periodic sequences.

The following notation is introduced in the drawing: 1 — a series of sequences of seismic vibrations with different frequency ranges of single actions, 2 — single quasi-sinusoidal pulses and skips of excitation in different sequences of series 1; 3 — autocorrelation functions of single pulses in various sequences of a series and the sum of autocorrelation functions of single pulses excited in various sequences; time interval - 4 excitations of one period of the seismic signal in the sequence; time interval - 5, occupied by the studied part of the response environment; the time interval is 6, during which a natural number of periods of the original signal in the sequence of the series is excited; time interval - 7 registration useful00

oh oh

signals or sequence duration; the time interval is 8, occupied by a single pulse or an excitation skip in different sequences of a series; unit impulse 9 with initial phase 0; unit impulse 10 with initial phase l; excitement skip 11; an autocorrelation function 12 of a single pulse consisting of one oscillation period; the autocorrelation function 13 of a single pulse consisting of two periods of oscillation; autocorrelation function 14 of a single impulse consisting of dust periods; autocorrelation function 15, is equal to the sum of the autocorrelation functions of 12, 13, and 14 single pulses.

The number of periods of the control signal is a natural number, and the number of periods of the reference signal is an integer.

The period of each sequence is formed from the ratios: 2n -1

TO

q

one

is -,

q-1 q2n + qn

K +

q n-bqn

(1) nat (1) now q q, p is a prime n, m is a ral number.

The structure of the follow-up of pulses and excitations in the sequence sequence of the series from which the control and correlation signals for each sequence are formed is determined in a known manner based on the solution of the recurrent equation, resulting in the period being formed as a linear recurrent sequence the numbers are +1, -1 and 0, respectively, with +1 corresponding to quadratic residues, -1 to quadratic non residues, and 0 to pulse skips. At the same time, a positive impulse with an initial phase O corresponds to +1, a negative impulse with a phase -P corresponds to -1.

The method is implemented by a known vibroseis instrumentation complex in the following sequence of operations.

The structure of the period of the original signal is calculated and formed in the manner described. To generate the control signals of the seismic source, the period of the original signal is cyclically continued, and the control signals are formed on the basis of both the integer and non-integer number of periods of the original signal. The original signal consisting of delta-shaped pulses is transformed into collar-variable

law of application, for example, by passing it through a filter whose pulse characteristic has the form of a single oscillatory pulse. In this way, for each sequence in the series, the control signal is fed to the actuator of the seismic source. The total number of single oscillatory pulses in the control

The 10 signal, which determines the amount of seismic energy transmitted to the medium, is set depending on the specified distribution of energy in the spectrum of the excited signals and the level of random noise

15 of the type of microseim in the area of work during the research.

The reference signal of the correlator during the development of each sequence of the series is formed in a similar way from the whole

20 number of periods of the original signal. The main one is the correlation mode with a reference signal formed from one period of the original signal. Pulses are used to form the reference signals.

25 identical in shape with oscillatory pulses used to generate control signals.

The reduction in the background of the correlation noise is ensured by the ideality of the periodic autocorrelation function, which is a consequence of the formation of the control and reference signals of the sequences in the series according to the above rule. The increase in resolution is provided by the ability to combine the spectra and the duration of different sequences in a series by varying the frequency bands of single pulses and their number.

40 After forming the control and reference signals of each sequence in the series, at each excitation point, the series of effects of the vibration seismic complex is tested according to the control signals and sequence parameters of the series shown in the drawing. Each vibrogram from each sequence of the series is recorded, each vibrogram is mutually correlated with its reference signal, and then all correlograms obtained (for example, 12, 13 and 14) are summed up and the resulting correlogram 15 is obtained, which is recorded on

55 magnetic carrier.

Claims (2)

Claim 1. Investigation method based on the excitation, registration and correlation processing of a series of sequences inverted by the initial phase of seismic effects of which the control and correlation signals in each sequence are formed from the same period of the original signal as periodic sequences of different polarized quasi-sinusoidal single impulses of the same duration following the same time interval, the period is not less than the recording time useful signals, characterized in that, in order to increase the resolution of seismic exploration, the control period a developing and reference signals are formed by interleaving in time identical in amplitude of individual pulses of different polarity and pulse passes in the form of a linear recursive sequence of pseudorandom numbers in which pulses correspond to single positive quadratic residues, negative - to quadratic non-evaluations, and pulse skips correspond to 0, the control signal is formed from the natural number of periods or from the Nelural number of periods, supplemented by a period segment, the duration of which is less than the registration time of useful signals, and the reference signal for correlation is formed from a whole the number of periods at In this case, the frequency composition of single pulses in different sequences of the series set different, and the resulting correlogram is obtained by summing the correlograms obtained from each sequences of the series, and the time interval between the sequences in the series set not less than the time of registration of useful signals. 2. A method according to claim 1, characterized in that the duration of the sequences in the series is different.