Earthquake first arrival picking system and method

Abstract

The present invention relates to the field of seismic exploration technology, and specifically discloses a seismic first arrival picking system and method. The system includes an acquisition device and a host computer, and the host computer has a preprocessing module, a calculation module and a comparison module, wherein the preprocessing module processes the seismic signals collected in each period T in real time and represents them as seismic wave amplitudes, and calculates the cumulative energy with time shift as the cumulative unit; the calculation module has multiple calculation units for taking logarithms, each calculation unit is provided with a stability factor, and the calculation unit is used to perform logarithmic operations on the cumulative energy under the corresponding set stability factor to obtain multiple rates of change of the cumulative energy; the comparison module is used to compare the multiple rates of change of the cumulative energy to obtain the maximum value of at least one group of rates of change, and the time shift corresponding to the maximum value of at least one group of rates of change is used as the picking result.

Description

Technical Field

[0001] The present invention relates to the field of seismic exploration technology, and in particular to a seismic first arrival picking method based on logarithmic cumulative energy change rate. Background Art

[0002] Determining the time of first arrival of earthquakes has always been a fundamental and crucial issue. In refraction and surface wave exploration, the travel time of first arrivals is often used to calculate surface velocity, layer thickness, and other medium parameters. In onshore seismic data processing, first arrival times are the basis for static correction of low-velocity zones on the surface. And in VSP data processing, the accuracy of first arrival times is crucial for the entire VSP data processing and interpretation process.

[0003] Many scholars at home and abroad have proposed a number of first-arrival picking methods. Traditional first-arrival picking methods can be divided into two main categories: the first category is based on the attribute characteristics of seismic records, such as the energy ratio method and the maximum amplitude method. The second category is based on the overall characteristics of seismic records, such as the correlation method and the statistical method. In addition, there are some other methods, such as fractal dimension method, neural network method, S-transform-based picking method, picking method based on single-channel boundary detection and spline interpolation, picking method based on mutual information, and comprehensive picking method combining multiple methods.

[0004] Seismic record attribute features are unique values extracted from seismic data related to geometry, kinematics, dynamics, or statistics. Based on the spatial distribution of these attributes, seismic attributes can be categorized as instantaneous, time-window, and planar (layer or slice) attributes. Currently, the most widely used first-arrival picking methods are based on seismic time-window attribute features, such as energy ratio, amplitude ratio, and curve length ratio. These methods are easy to implement, offer high picking efficiency, and provide relatively good results.

[0005] First-arrival picking methods based on seismic time window attributes all use the ratio of the energy sum (amplitude sum / curve length) after and before the calculated time window as the characteristic value. Therefore, the choice of time window has a significant impact on the efficiency and accuracy of picking. The most primitive approach uses a fixed time window, but in most cases, the first-arrival times picked using this fixed time window method are inaccurate. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a method for picking earthquake first arrivals based on the logarithmic cumulative energy change rate.

[0007] To achieve the above object, the present invention provides a seismic first arrival picking system, comprising:

[0008] An acquisition device, used to continuously acquire seismic signals on the seismic trace according to a set period T;

[0009] The host computer has a preprocessing module, a calculation module and a comparison module, among which,

[0010] The pre-processing module and the acquisition device have the same reference timing. The pre-processing module includes a conversion unit and an accumulator. The conversion unit is used to process the seismic signals collected in each period T in real time and express them in terms of seismic wave amplitude, and input them into the accumulator according to the corresponding timing. The accumulator calculates the accumulated energy based on the continuously received seismic wave amplitude with the time shift as the accumulation unit.

[0011] The calculation module has a plurality of calculation units for taking logarithms, each of which is provided with a stability factor, and the calculation unit performs a logarithmic operation on the accumulated energy under the corresponding stability factor to obtain a plurality of change rates of the accumulated energy;

[0012] The comparison module is used to compare the change rates of the cumulative energies to obtain a maximum value of at least one set of change rates, and to use the time shift corresponding to the maximum value of at least one set of change rates as a picking result.

[0013] Furthermore, clock chips are respectively provided in the acquisition device and the pre-processing module to provide the same reference timing for the pre-processing module and the acquisition device.

[0014] Furthermore, an input portion is provided in the calculation module, and the input portion is connected to the calculation units respectively;

[0015] The calculation unit is provided with a reference part, and the reference part is used to input the corresponding stability factor according to the input part.

[0016] Furthermore, the plurality of computing units are arranged in sequence according to a set order, and the stability factors of the plurality of computing units gradually increase according to a set base number in the set order.

[0017] Furthermore, a correction module is also provided in the host computer, which is used to calibrate the waveform characteristics at any moment obtained with reference to the time shift corresponding to the picking result, and when the waveform characteristics tend to be stable, the picking result is selected as the final result.

[0018] The present invention also provides a method for picking up an earthquake first arrival, comprising the following steps:

[0019] Step 1) continuously collecting seismic signals on the seismic trace according to a set period T;

[0020] Step 2) Processing the seismic signals collected in each period T in real time and expressing them as seismic wave amplitudes, and calculating the cumulative energy using the time shift as the cumulative unit;

[0021] Step 3) performing a logarithmic operation on the cumulative energy under a correspondingly set stability factor by a calculation unit to obtain a plurality of rates of change of the cumulative energy;

[0022] Step 4) compares the rates of change of the cumulative energy to obtain at least one set of maximum values of the rates of change, and uses the time shift corresponding to the at least one set of maximum values as the picking result. In step 4), the waveform feature is calibrated using the waveform feature at any time obtained with the time shift as a reference, corresponding to the picking result. When the waveform feature tends to be stable, the picking result is selected as the final result.

[0023] By calculating the logarithmic cumulative energy change rate from seismic traces, we can automatically pick up earthquake first arrivals and automatically track seafloor reflections. This method uses automatic data collection and calculation, resulting in a simple algorithm and stable and reliable results. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the system structure principle diagram of the present invention;

[0025] Figure 2 is a flow chart of the method of the present invention;

[0026] Figure 3 A single simulated seismic trace record is the result of picking;

[0027] Figure 4 Results of low signal-to-noise ratio simulation data picking (SNR = 1, stability factor = 100);

[0028] Figure 5 Picking error of low signal-to-noise ratio simulated data (SNR = 1, stability factor = 100);

[0029] Figure 6 High signal-to-noise ratio simulation data picking results (SNR = 4, stability factor = 10);

[0030] Figure 7 Picking error of high signal-to-noise ratio simulated data (SNR = 4, stability factor = 10);

[0031] Figure 8 Actual seismic data picking result 1;

[0032] Figure 9 Actual seismic data picking result 2. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] Example 1

[0035] The present invention provides a seismic first arrival picking system, comprising:

[0036] An acquisition device is used to continuously acquire seismic signals on the earthquake first-arrival seismic trace according to a set period T;

[0037] The host computer has a preprocessing module, a calculation module and a comparison module, among which,

[0038] The pre-processing module and the acquisition device have the same reference timing. The pre-processing module includes a conversion unit and an accumulator. The conversion unit is used to process the seismic signals collected in each period T in real time and express them in terms of seismic wave amplitude, and input them into the accumulator according to the corresponding timing. The accumulator calculates the accumulated energy based on the continuously received seismic wave amplitude with the time shift as the accumulation unit.

[0039] The calculation module has a plurality of calculation units for taking logarithms, each of which is provided with a stability factor, and the calculation unit performs a logarithmic operation on the accumulated energy under the corresponding stability factor to obtain a plurality of change rates of the accumulated energy;

[0040] The comparison module is used to compare the change rates of the cumulative energies to obtain a maximum value of at least one set of change rates, and to use the time shift corresponding to the maximum value of at least one set of change rates as a picking result.

[0041] Furthermore, clock chips are respectively provided in the acquisition device and the pre-processing module to provide the same reference timing for the pre-processing module and the acquisition device.

[0042] Furthermore, an input portion is provided in the calculation module, and the input portion is connected to the calculation units respectively;

[0043] The calculation unit is provided with a reference part, and the reference part is used to input the corresponding stability factor according to the input part.

[0044] Furthermore, the plurality of computing units are arranged in sequence according to a set order, and the stability factors of the plurality of computing units gradually increase according to a set base number in the set order.

[0045] Furthermore, a correction module is also provided in the host computer, which is used to calibrate the waveform characteristics at any moment obtained with reference to the time shift corresponding to the picking result, and when the waveform characteristics tend to be stable, the picking result is selected as the final result.

[0046] The present invention also provides a method for picking up an earthquake first arrival, comprising the following steps:

[0047] Step 1) continuously collecting seismic signals on the seismic trace according to a set period T;

[0048] Step 2) Processing the seismic signals collected in each period T in real time and expressing them as seismic wave amplitude and cumulative energy with time shift as the cumulative unit;

[0049] Step 3) performing a logarithmic operation on the cumulative energy under a correspondingly set stability factor by a calculation unit to obtain a plurality of rates of change of the cumulative energy;

[0050] Step 4) compares the rates of change of the cumulative energy to obtain at least one set of maximum values of the rates of change, and uses the time shift corresponding to the at least one set of maximum values as the picking result. In step 4), the waveform feature is calibrated using the waveform feature at any time obtained with the time shift as a reference, corresponding to the picking result. When the waveform feature tends to be stable, the picking result is selected as the final result.

[0051] Example 2

[0052] This embodiment is a further explanation of embodiment 1.

[0053] Theoretically, the energy characteristics of a seismic trace before and after the first arrival should differ significantly, because the effective seismic signal before it is zero, with only relatively weak noise present, while the seismic signal after it is relatively strong. Therefore, near the first arrival, the energy of the seismic trace should experience a sudden change, which can be reflected in the cumulative energy change rate. Similar to the correlation function method, we can also calculate the cumulative energy function based on the time shift τ:

[0054]

[0055] Where s(t) is the seismic trace record.

[0056] Calculate the rate of change of the cumulative energy function. The point with the largest rate of change usually corresponds to the first arrival time. However, when the noise in the seismic trace is severe, the cumulative energy rate of change may fail, resulting in inaccurate picking results. A feasible approach is to first add a stabilization factor B to the cumulative energy, then take the logarithm, and then calculate the rate of change:

[0057] LogE acc (τ) = log 10 (E acc (τ)+B)

[0058]

[0059] Among them, logE acc (τ) is the logarithmic form of the cumulative energy function plus the stability factor, referred to as logarithmic cumulative energy, logE′ acc (τ) is the logarithmic derivative of the cumulative energy function plus the stabilization factor, that is, the rate of change of the logarithmic cumulative energy function.

[0060] Generally speaking, the time shift τ corresponding to the maximum value of the rate of change is near the first arrival time. When the waveform of the source wavelet is sufficiently stable, the difference between the time shift τ and the first arrival time is also stable. The above-mentioned first arrival picking result can be further corrected by calibrating the waveform characteristics of the source wavelet.

[0061] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. Earthquake first arrival picking system, characterized by: include: An acquisition device, used to continuously acquire seismic signals on the seismic trace according to a set period T; The host computer has a preprocessing module, a calculation module and a comparison module, among which, The pre-processing module and the acquisition device have the same reference timing. The pre-processing module includes a conversion unit and an accumulator. The conversion unit is used to process the seismic signals collected in each period T in real time and express them in terms of seismic wave amplitude, and input them into the accumulator according to the corresponding timing. The accumulator calculates the accumulated energy based on the continuously received seismic wave amplitude with the time shift as the accumulation unit. The calculation module has a plurality of calculation units for taking logarithms, each of which is provided with a stability factor, and the calculation unit performs a logarithmic operation on the accumulated energy under the corresponding stability factor to obtain a plurality of change rates of the accumulated energy; The comparison module is used to compare the change rates of the cumulative energies to obtain a maximum value of at least one set of change rates, and to use the time shift corresponding to the maximum value of at least one set of change rates as a picking result.

2. The earthquake first arrival picking system according to claim 1, characterized in that: The acquisition device and the pre-processing module are respectively provided with clock chips to provide the same reference timing for the pre-processing module and the acquisition device.

3. The earthquake first arrival picking system according to claim 1, characterized in that: An input portion is provided in the calculation module, and the input portion is connected to the calculation units respectively; The calculation unit is provided with a reference part, and the reference part is used to input the corresponding stability factor according to the input part.

4. The earthquake first arrival picking system according to claim 1, characterized in that: The plurality of computing units are arranged in sequence according to a set order, and the stability factors of the plurality of computing units gradually increase according to a set base number according to the set order.

5. The earthquake first arrival picking system according to claim 1, characterized in that: The host computer is also provided with a correction module, which is used to calibrate the waveform characteristics at any moment obtained with reference to the time shift corresponding to the picking result. When the waveform characteristics tend to be stable, the picking result is selected as the final result.

6. The earthquake first arrival picking method is characterized by: The steps include: Step 1) continuously collecting seismic signals on the seismic trace according to a set period T; Step 2) Process the seismic signals collected in each period T in real time and express them as seismic wave amplitudes, and calculate the cumulative energy using the time shift as the cumulative unit; Step 3) performing a logarithmic operation on the accumulated energy under a corresponding set stability factor by a calculation unit to obtain a plurality of change rates of the accumulated energy; Step 4) comparing the change rates of the cumulative energies to obtain at least one set of maximum values of the change rates, and taking the time shift corresponding to the at least one set of maximum values of the change rates as the picking result.

7. The earthquake first arrival picking method according to claim 6, characterized in that: In step 4), the waveform feature at any moment corresponding to the picked result and obtained with reference to the time shift is calibrated, and when the waveform feature tends to be stable, the picked result is selected as the final result.

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