A vibrator efficient scanning method and system based on harmonic frequency doubling characteristics

Abstract

The present invention provides a method and system for efficient scanning of a controllable vibrator based on harmonic frequency doubling characteristics, which belongs to the field of controlled vibrator seismic exploration and acquisition. The method utilizes the frequency doubling characteristics of harmonics and converts harmonics into effective signals through frequency doubling scanning, thereby expanding the effective bandwidth of the source and improving the resolution of the seismic wavelet. The present invention can simultaneously meet the two requirements of improving production efficiency and data signal-to-noise ratio, and can be applied to independent synchronous scanning. Harmonics are effective signals, which effectively broaden the actual seismic bandwidth of the source and improve the wavelet resolution. The present invention can meet the technical requirements of existing types of controllable vibrators and is suitable for efficient acquisition of controllable vibrators.

Description

Technical Field

[0001] The present invention belongs to the field of vibroseis seismic exploration and acquisition, and in particular relates to a vibroseis efficient scanning method and system based on harmonic frequency doubling characteristics. Background Art

[0002] Seismic source is a key technology in oil and gas seismic exploration.

[0003] Seismic sources can be divided into two categories based on their application area: onshore and underwater. Based on their wavelet morphology, onshore sources can be further divided into pulse and non-pulse sources. Pulse sources include well-emplacement explosive sources, percussive hammer sources, land-based airgun sources, aerial explosive packs, explosive cords, shaped charges, and seismic guns. Non-pulse sources include detectable sources and Sosie sources. Explosives and vibrators are the most commonly used in onshore seismic exploration.

[0004] Compared with explosive sources, controllable vibrators have four outstanding advantages:

[0005] · It does not generate vibration frequencies that are not propagated by the formation, and the frequency band most suitable for formation propagation can be selected as the scanning frequency band.

[0006] Does not damage rocks and does not consume energy in rock crushing.

[0007] Strong anti-interference ability. The controllable vibrator adopts relevant technology to avoid many interferences and improve the signal-to-noise ratio of data.

[0008] It causes little damage to the ground and is particularly suitable for work in densely populated areas, hard ground, and Gobi deserts.

[0009] With the widespread use of vibrators in seismic exploration, many new research results have emerged in recent years, mainly focusing on how to improve the operation efficiency and data quality of vibrators. The main vibrator technologies used in seismic acquisition are:

[0010] -Alternating Scan (AS) method

[0011] -Time Sliding Scan (TSS) method

[0012] - Independent Synchronous (ISS) scanning method

[0013] -Distance-synchronous scanning (D3S) method

[0014] -High-Fidelity Vibroseis Seismic (HFVS) Method

[0015] Alternating scanning is called conventional acquisition of controlled source, and the other is called high-efficiency acquisition of controlled source.

[0016] The application of controllable vibrators also has its limitations. From a technical perspective: first, the ground excitation of controllable vibrators will generate strong surface waves; second, the limited scanning bandwidth reduces the resolution of the wavelet to a certain extent; third, affected by the mechanical properties of the vibrator, the continuous scanning time at the low and high frequency ends is short; third, multiple harmonics are generated, which affects the seismic single-shot noise ratio in the efficient acquisition of controllable vibrators.

[0017] Data quality and operational efficiency for specific scanning methods are characterized by the following: Alternating Scanning (AS) offers high single-shot SNR but low operational efficiency; Time Sliding Scanning (TSS) suffers from strong harmonic interference, resulting in a low single-shot SNR, but high operational effectiveness; Independent Synchronous Scanning (ISS) suffers from strong interference, a low SNR, and high operational efficiency; Distance-Dependent Synchronous Scanning (D3S) offers high single-shot SNR and higher operational efficiency than AS, but requires more equipment investment; High-Fidelity Vibroseis Seismic (HFVS) offers high SNR and high operational efficiency, but requires more equipment (sources) and requires extensive in-house data processing. Because the high-efficiency acquisition method of vibroseis yields a shift in single-shot SNR, higher-order coverage is often used to compensate for the shortcomings of single-shot data. In practice, bin coverage generally follows the order: ISS > TSS > D3S > HFVS > AS.

[0018] TSS, D3S and AS are the three most common scanning methods in production.

[0019] Currently, the time efficiency of vibroseis acquisition and the signal-to-noise ratio of a single shot are negatively correlated. Data indicates that independent synchronous scanning (ISS) is the most time-efficient scanning method for vibroseis seismic acquisition, reaching over 1,000 shots per hour, but with a low signal-to-noise ratio. Alternating scanning (AS) offers a high signal-to-noise ratio per shot but low efficiency, at 100 shots per hour.

[0020] Chinese patent publication CN103777240A discloses a frequency band compensation method for frequency-scanning controllable seismic sources. The method collects seismic data from the study area, analyzes the spectrum of the target layer of the original data, recognizes and understands the frequency bands and energy that need to be compensated, establishes an absorption model, and performs numerical simulation of viscoelastic media based on independent frequency band technology. The simulation results are used to statistically determine the scanning time of each frequency band to compensate for stratum absorption, widen the frequency band, and apply it to deep high-resolution exploration. However, this patent estimates the absorption attenuation of the stratum through frequency scanning and specifically designs the scanning time, that is, different scanning times are used for different frequency bands to compensate for the attenuation of different frequency bands; moreover, this patent is applied to related post-data and does not consider the suppression and application of harmonics. It is unrelated to the source equipment, resulting in the patent being unable to utilize the characteristic of the controllable seismic source to generate harmonics to eliminate and apply harmonics. Summary of the Invention

[0021] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and to provide a method and system for efficient scanning of a controllable seismic source based on harmonic frequency doubling characteristics, which can simultaneously meet the two requirements of improving production efficiency and data signal-to-noise ratio, and also meet the requirements of broadening the effective bandwidth and improving the wavelet resolution.

[0022] The present invention is achieved through the following technical solutions:

[0023] The first aspect of the present invention provides an efficient scanning method for a controllable seismic source based on the harmonic frequency doubling characteristics. The method utilizes the frequency doubling characteristics of harmonics and converts harmonics into effective signals through frequency doubling scanning, thereby expanding the effective bandwidth of the seismic source and improving the resolution of the seismic wavelet.

[0024] A further improvement of the present invention is:

[0025] The method comprises:

[0026] Step 1: Design the bandwidth of the synthetic sweep signal;

[0027] Step 2: Design the segment scanning duration;

[0028] Step 3: Conduct field construction to obtain continuous relevant pre-scan data of all shot points;

[0029] Step 4: Perform data cropping and single-shot reconstruction on the pre-correlation data to obtain the post-correlation seismic records.

[0030] A further improvement of the present invention is:

[0031] The operation of step 1 includes:

[0032] The bandwidth of the synthetic scanning signal is the difference between the cutoff frequency and the starting frequency of the scanning signal;

[0033] The cutoff frequency is 2 to the power of the start frequency.

[0034] A further improvement of the present invention is:

[0035] The operation of step 1 further includes:

[0036] From the starting frequency to the cutoff frequency, the frequency is divided into N scanning segments;

[0037] The cutoff frequency of each scanning segment is a multiple of the starting frequency, and the difference between the cutoff frequency and the starting frequency is the scanning bandwidth of the scanning segment.

[0038] A further improvement of the present invention is:

[0039] The operation of step 2 includes:

[0040] The duration of the long linear scan is evenly distributed according to the scan segments to obtain the scan duration of each scan segment.

[0041] A further improvement of the present invention is:

[0042] The operation of step 3 includes:

[0043] At the designed shot point position, scan randomly according to the scan bandwidth and scan duration of each scan segment, and continuously record the relevant previous data;

[0044] Each shot point position is scanned N times.

[0045] A further improvement of the present invention is:

[0046] The data clipping operation in step 4 includes:

[0047] (41) Sort the relevant front data according to the scanning bandwidth and scanning duration of each scanning segment;

[0048] (42) The scanning time of each scanning segment plus the listening time is used as the clipping time, and the relevant front data is clipped using the clipping time to form the relevant front single shot.

[0049] The single shot reconstruction operation in step 4 includes:

[0050] (43) performing correlation calculation on the pre-correlation single shot to form a post-correlation record;

[0051] (44) Reconstruct the relevant post-records according to the positions of each shot point to obtain the relevant post-seismic records corresponding to each shot point;

[0052] (45) The heavy guns are separated to obtain the vibroseis-correlated post-seismic records of all gun points without harmonic interference.

[0053] A second aspect of the present invention provides a vibroseis efficient scanning system based on harmonic frequency multiplication characteristics, the system comprising:

[0054] Bandwidth design unit: used to design the bandwidth of the synthetic scanning signal;

[0055] Duration design unit: used to design the segmented scanning duration;

[0056] Acquisition unit: used to collect continuous relevant pre-data of all shot point segmented scanning obtained during field construction;

[0057] Processing unit: connected to the acquisition unit, used to perform data clipping and single-shot reconstruction on the pre-correlation data to obtain the post-correlation seismic records.

[0058] The third aspect of the present invention provides a computer-readable storage medium, which stores at least one computer-executable program. When the at least one program is executed by the computer, the computer executes the steps of the above-mentioned controllable seismic source efficient scanning method based on harmonic frequency doubling characteristics.

[0059] Compared with the existing technology, the beneficial effects of the present invention are: the present invention can simultaneously meet the two requirements of improving production efficiency and data signal-to-noise ratio, can be applied to independent synchronous scanning, harmonics are effective signals, effectively broaden the actual seismic bandwidth of the source, and improve the wavelet resolution; the present invention can meet the technical requirements of existing types of controllable seismic sources and is suitable for efficient acquisition of controllable seismic sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 Aliasing acquisition - theoretical basis of vibroseis seismic excitation;

[0061] Figure 2 Spectrum of source force signal excited by vibrator;

[0062] Figure 3-1 Data before separation - common shot gather;

[0063] Figure 3-2 The separated data R=3;

[0064] Figure 4 relevant previous records;

[0065] Figure 5-1 Seismic recording of 8-16Hz sweep signal

[0066] Figure 5-2 Seismic recording of 16-32Hz sweep signal

[0067] Figure 5-3 Seismic recording of 32-64Hz sweep signal

[0068] Figure 5-4 Seismic recording of 64-128Hz sweep signal

[0069] Figure 6 A scanning signal synthesized from a 5-10Hz fundamental signal and 1 / 2 to 8th order harmonics

[0070] Figure 7-1 1 / 2 order harmonic (2.5-5Hz)

[0071] Figure 7-2 It is the 4th order harmonic (20-40Hz)

[0072] Figure 7-3 Fundamental wave (5-10Hz)

[0073] Figure 7-4 8th order harmonic (40-80Hz)

[0074] Figure 7-5 It is the second-order harmonic (10-20Hz)

[0075] Figure 7-6 It is a synthesis of fundamental wave and harmonics;

[0076] Figure 8 A block diagram of the steps of the method of the present invention. DETAILED DESCRIPTION

[0077] The present invention is further described in detail below with reference to the accompanying drawings:

[0078] Improving seismic resolution is one of the goals of seismic exploration. Compared to explosive sources, the limited scanning bandwidth of controllable vibrators limits the resolution of seismic wavelets. The method of the present invention utilizes the frequency-doubling characteristics of harmonics and converts them into effective signals through frequency-doubling scanning. This, to a certain extent, expands the effective bandwidth of the source and improves the resolution of seismic wavelets, making it more conducive to the exploration of lithologic oil and gas reservoirs.

[0079] The principle of the inventive method is as follows:

[0080] The vibrator is a continuous single-frequency aliasing acquisition. Therefore, the vibrator signal can be decomposed into countless simple harmonic signals, and countless simple harmonic signals with different frequencies can be superimposed to form a pulse signal, such as Figure 1 As shown in the figure, in addition to the effective signal, there are also harmonics in the source scanning. Harmonics occur simultaneously with the scanning signal. Harmonics are usually integer multiples of the scanning signal. There are also non-integer multiple harmonics such as 1 / 2, 3 / 2, and 5 / 2. However, the energy of non-integer multiple harmonics is weaker than that of integer multiple harmonics. Figure 2 shown.

[0081] Assume that the source scanning signal is F(ω 1 ,ω 2 ), the first-order harmonic is F 1 (2ω 1 , 2ω 2 ), the second-order harmonic is F 2 (4ω 1 , 4ω 2 ), the third-order harmonic is F 3 (8ω 1 , 8ω 2 ), the Nth order harmonic is F N-1 (2 N ω 1 , 2 N ω 2 ), non-integer harmonics are F (2N-1) / 2 (3*2 N-1 ω 1 / 2, 3*2N-1 ω 2 / 2).

[0082] The vibrator is a continuous single-frequency mixed acquisition, which is expressed in the form of a linear sweep signal:

[0083]

[0084] Among them: m represents the source number; a m (t) represents the output of each earthquake source;

[0085] f1, f2 represent the starting frequency and cutoff frequency;

[0086] T represents the scan length;

[0087] Represents the sweep slope.

[0088] Assume that the frequency slice of the iωth earthquake source at any spatial position is w iω (x, y, z), then the scanning signal of the ith frequency slice of the Ns sources can be expressed as:

[0089]

[0090] Where: is the scanning signal of the iωth frequency slice of the first source.

[0091] The source coding of Ns shots can be represented by the coding matrix:

[0092]

[0093] Where: a represents the amplitude code, which can be understood as the magnitude of the source output; is the phase encoding. N S is the gun number, representing the Nth S Cannon, N e Is the frequency chip number, representing the Nth e Frequency chip.

[0094] The encoding process uses matrix multiplication The aliasing source of all frequencies can be expressed as:

[0095]

[0096] The uncorrelated supershot gathers obtained after the action of the wave propagation operator L are:

[0097]

[0098] The signal decoding is to use the correlation between the scanning signal of each source and the aliased acquired shot gathers, and perform conjugate multiplication in the frequency domain:

[0099]

[0100] The records of all frequency slices nω can be represented by a 1×nω matrix:

[0101]

[0102] The correlation results between the scan signal of the is-th shot and the aliased collected data are:

[0103]

[0104] In addition to the scanning signal, the source also generates resonance. The correlation between the scanning signal of the isth shot and the aliased data can be expressed as:

[0105]

[0106] Among them: the first term on the right side of formula (1-9) is the autocorrelation of the is-th shot scanning signal, defined as the seismic record; the second term is the cross-correlation between the is-th shot scanning signal and the source resonance; the third term is the cross-correlation between the is-th shot scanning signal and other source signals.

[0107] Without loss of generality, assume that there are only two shots in the aliasing acquisition. The correlation between the first shot signal and the two-shot aliasing data is:

[0108]

[0109] The autocorrelation of the signal is 1. It is 0 when the signal has no crossover frequency with harmonics or other scanning signals. That is, the cross-correlation between the signal and its integer multiple harmonics is 0 (non-integer multiple harmonics have weak energy and little impact, so they are not considered for now). Assuming ISS is used, the cross-correlation between the signal of the Nth shot and the signal of the N-1th shot is 0, and its harmonics (integer) are 0 or 1. The condition is that the scanning signal of the Nth shot is a multiple of the N-1th shot. The effective scanning frequency band is divided into 5 segments, and Equation (1-10) is designed as Table 1 as follows:

[0110]

[0111] Table 1

[0112] Valid records obtained by correlating the same signal are counted as 1, and records obtained by correlating different signals are counted as 0. The first scanning signal is ω-2ω, and the second to sixteenth harmonics are 2ω-4ω, 4ω-8ω, 8ω-16ω, and 18ω-32ω, respectively, which are the same as the scanning signals of the second to fifth sections. Assuming that the scan signal and its different-order harmonics are independent or separable (in accordance with the aliasing acquisition principle), the first scan segment is correlated with the signals of the first to fifth segments. The autocorrelation of the scan signal is 1, and the cross-correlation with the second to fifth scan segments is 0, resulting in a record labeled 1+0+0+0+0. Similarly, the first to fifth scan segments are cross-correlated with the first-order harmonic in the first segment, yielding 0+1+0+0+0; cross-correlating with the second-order harmonic yields 0+0+1+0+0; cross-correlating with the third-order harmonic yields 0+0+0+1+0; and cross-correlating with the fourth-order harmonic yields 0+0+0+0+1. The combined record yields 1+1+1+1+1. The same method is used to obtain the records of the second to fifth segments, as shown in Table 2.

[0113]

[0114] Table 2

[0115] Theoretically, if the fifth-order harmonic of the mixed record is used for cross-correlation, a wider frequency seismic record can be obtained. Similarly, if the 1 / 2-order cross-correlation of the first-segment sweep signal is used for the first-segment sweep record, a lower frequency seismic record can also be obtained.

[0116] Continuous scanning records can be cut and synthesized to obtain single shots of independent sources. Taking Table 1 as an example, the most complex case is that the five-segment scan is caused by random synchronous excitation of five sources at a certain distance. Assuming that the continuous scanning time is L, the earthquake recording time is T, the recording time is L+T, and the scanning time of the first segment of sources S1, S2, S3, S4, and S5 is T1 respectively. 10 -T1 11 , T2 10 -T2 11 , T3 10 -T3 11 , T4 10 -T4 11 , T5 10 -T5 11 , the second scanning time is T1 20 -T1 21 , T2 20 -T2 21 , T3 20 -T3 21 , T4 20 -T4 21 , T5 20 -T5 21 , ..., the Nth segment scanning time is T1N0 -T1 N1 , T2 N0 -T2 N1 , T3 N0 -T3 N1 , T4 N0 -T4 N1 , T5 N0 -T5 N1 , a total of 5N scanning periods.

[0117] Earthquake Records L For the related previous record. L The 5N scanning periods are cross-correlated with the scanning signals or force signals of S1, S2, S3, S4, and S5, respectively, to obtain 25N scanning records.

[0118] Since harmonics and source scanning have isochronous characteristics, the records are recorded according to T1 10+T , T2 10+T , T3 10+T , T4 10+T , T5 10+T , T1 20 +T1 , T2 20+T , T3 20+T , T4 20+T1 , T5 20+T1 ,……,T1 N0+T , T2 N0+T , T3 N0+T , T4 N0+T , T5 N0+T , and cut them, synthesize and reconstruct them according to the source classification to obtain the earthquake records of independent sources S1, S2, S3, S4, and S5, totaling 5N.

[0119] Synchronous scanning, when the high-frequency harmonics in the low frequency band are the same as the high frequency band scanning signal, a heavy gun phenomenon similar to that of explosive source excitation is generated. In the data processing process, multi-domain or high-dimensional denoising and separation technology can be used to perform denoising and shot collection separation. Figure 3-1 and Figure 3-2 This is the comparison of three-dimensional simulation data before and after separation, and R=3 is the separation dimension.

[0120] The present invention is frequency-multiplied independent synchronous scanning (FDISS), which can be applied to independent synchronous scanning signal design. The forward simulation scanning frequencies are S1: 8-16Hz; S2: 16-32Hz; S3: 32-64Hz; S4: 64-132Hz, the scanning time is 4s, and the listening time is 2s. Figure 4 These are related records, and the records interfere with each other seriously. Figure 4This is the record before the correlation of the theoretical model forward simulation [S1(100,0): 8-16Hz; S2(200,0): 16-32Hz; S3(300,0): 32-64Hz; S4(400,0): 64-132Hz, scanning time 4s; listening time 2s]

[0121] right Figure 4 The records are correlated with the scanning signals to obtain seismic records of different scanning signals, such as Figure 5-1 to Figure 5-4 As shown, from Figure 5-1 to Figure 5-4 It can be seen that the record has a high signal-to-noise ratio. The forward simulation shows that the frequency-divided independent synchronous scanning is suitable for vibroseis seismic acquisition.

[0122] The frequency-doubling independent synchronous scanning (FDISS) method of the present invention can convert harmonics into effective waves, expand the scanning bandwidth, and improve the seismic wavelet resolution.

[0123] The fundamental signal is designed to be 5-10Hz, the low-order harmonic is 2.5-5Hz, the first-order harmonic is 10-20Hz, the second-order harmonic is 20-40Hz, and the third-order harmonic is 40-80Hz. The synthesized scanning signal is as follows: Figure 6 shown.

[0124] The comparison between the wavelet after correlation between fundamental wave and harmonic wave and the synthesized wavelet is as follows: Figures 7-1 to 7-6 As shown, from Figures 7-1 to 7-6 It can be seen that after the fundamental wave and harmonic signals are synthesized, they become a broadband sub-wave, and the harmonics become effective signals.

[0125] The embodiments of the inventive method are as follows:

[0126] [Example 1]

[0127] The present invention provides a basis for the transformation of seismic source equipment. To address the problem that the low-frequency and high-frequency bands of existing controllable seismic sources cannot be scanned for a long time, the first approach is to develop low-frequency and high-frequency controllable seismic sources in a targeted manner to make their mechanical properties more adaptable; the second approach is to develop harmonic controllable seismic sources and use harmonics to expand the scanning bandwidth.

[0128] The present invention provides a vibroseis efficient scanning method based on harmonic frequency multiplication characteristics, such as Figure 8 As shown, it includes four steps:

[0129] Step 1: Design the bandwidth of the synthetic sweep signal:

[0130] The bandwidth of a synthetic sweep signal refers to the difference between the cutoff frequency and the starting frequency of the sweep signal. The design of the bandwidth follows the same principles as conventional vibroseis signal design, with the difference being that the cutoff frequency is equal to the starting frequency raised to the power of 2N, and is usually greater than or equal to 5 octaves, meaning N is greater than or equal to 5. During segmented sweeping, the frequency is divided into N sweep segments, with the cutoff frequency of each sweep segment being a multiple of the starting frequency. The difference between the cutoff frequency and the inspiration frequency of each sweep segment is the sweep bandwidth of that sweep segment, as follows:

[0131] The first section is: ω-2ω, the second section is: 2ω-4ω, the third section is: 4ω-8ω, the fourth section is: 8ω-16ω, and so on. If the starting frequency is 3Hz, the first section is: 3-6Hz, the second section is: 6-12Hz, the third section is: 12-24Hz, the fourth section is: 24ω-48ω, the fifth section is: 48ω-96ω, and so on.

[0132] The starting frequency ω is determined according to the mechanical properties of the source. Taking up-scanning as an example, the low-frequency source is usually 1.5-2Hz, and the general source is 3-4Hz. The specific frequency can be determined by referring to the source performance.

[0133] The present invention is applied to a vibroseis signal, which is expressed as follows:

[0134]

[0135] Where S(t) is the signal in the S matrix, A(t) is the amplitude of the signal, and f s is the starting frequency of the signal, f e is the cutoff frequency of the signal, t is the time, Φ is the phase, and T is the scanning duration.

[0136] Determine f according to the geological task needs s and f e , the frequency is determined.

[0137] In step 1, the cutoff frequency is required to be equal to 2 times the starting frequency. n The segmented scanning cut-off frequency is a multiple of the starting frequency (n is an integer), which ensures that the high-order harmonics and the high-frequency scanning signal have the same bandwidth. After correlation, the high-order harmonics can be converted into effective signals.

[0138] Step 2: Design the segment scan duration.

[0139] A relatively simple method is to evenly distribute the duration of a long linear scan (generally 30-48s) by scan segments. Its advantages are simplicity, and the high-order harmonics and the high-frequency band scan signal have the same scan length, which is conducive to record cropping, separation and reconstruction.

[0140] A more scientific method is to filter the seismic records of different scanning lengths in the past according to the segmented designed scanning frequency bands, or to conduct different scanning length tests according to the designed scanning frequency bands, and select the optimal scanning time for different frequency bands based on the signal-to-noise ratio of the target layer. Its advantage is that it ensures that different scanning frequency bands have the maximum signal-to-noise ratio, but because the scanning time of different segments is different, it is not conducive to record cropping.

[0141] Considering actual production efficiency, the present invention adopts the same scanning time.

[0142] In step 2, through the frequency doubling scanning analysis of previous data or test data of different durations, based on the signal-to-noise ratio of the target layer, the mechanical properties of the controllable source should be fully considered when selecting the scanning duration. That is, the high-frequency and low-frequency scanning servo times of the controllable source have certain limitations. In principle, the mid-frequency scanning duration is mainly matched with the low-frequency and high-frequency scanning durations. Assuming that the high-frequency and low-frequency scanning servo times of the controllable source are limited to 5S, the segmented scanning duration is preferably 3.5-4S. First, it meets the safe production requirements of field equipment; second, the mid-frequency data usually has a higher signal-to-noise ratio, and appropriately shortening the scanning duration has little impact on the data.

[0143] Step 3: Conduct field construction to obtain continuous relevant pre-scan data of all shot points;

[0144] The construction process is basically the same as the conventional AS, with the following two differences:

[0145] (31) At the designed shot point position, random scanning is performed according to the segmented designed scanning bandwidth and scanning duration (random refers to the scanning time, that is, each source can independently scan at any time according to the designed scanning bandwidth and duration). Similar to HFVS scanning, the number of scans at each shot point position is N steps, which is the same as the number of scanning segments N in step 1;

[0146] (32) Continuously record relevant previous data;

[0147] Conventional AS construction processes do not record relevant previous data, and the records are not continuous.

[0148] Step 3 obtains the continuous pre-correlation data of segmented scanning of all source points. The difference from AS and other post-correlation records is that in the seismic records, in addition to the fundamental signal, the seismic information of high-order harmonics is retained, laying a data foundation for the separation and application of harmonic signals.

[0149] Step 4: Perform data cropping and single-shot reconstruction on the pre-correlation data to obtain the post-correlation seismic records.

[0150] The steps for data trimming are as follows:

[0151] (41) Sort the pre-correlation data (pre-correlation data of all shot points within the same segmented scanning frequency) by segmented scanning bandwidth and scanning time;

[0152] (42) The scanning time of the segmented scan is added to the listening time (listening time refers to the length of a single shot record) as the clipping time. The relevant front data is clipped using the clipping time (the clipping is performed using existing methods, which will not be described here). This forms the relevant front single shot. If the number of shot points is designed to be Ns, and each shot point is scanned N times, the number of clipped relevant front single shots is N×Ns.

[0153] The steps for single-shot reconstruction are as follows:

[0154] (43) Correlation calculations are performed on the pre-correlation single shot, including fundamental wave correlation and harmonic wave correlation calculations (implemented using existing technology and not described here in detail), to form post-correlation records. Theoretically, N post-correlation records can be obtained for each shot point and each scan segment.

[0155] In step 1, the segmented scanning cutoff frequency is a multiple of the starting frequency. Therefore, the high-order harmonics of any frequency segment will always correspond to the fundamental signal of another frequency segment. As shown in Table 1, the theoretical results of the relevant calculations meet the requirements of Table 2, realizing the separation and application of harmonics.

[0156] (44) The related post-records are reconstructed according to the positions of each shot point, that is, the related post-records after the shot point segmentation clipping are vertically stacked (implemented using existing technology, which will not be repeated here), to obtain the related post-seismic records corresponding to each shot point.

[0157] When reconstructing post-correlation records by shot location, the possible differences in energy or signal-to-noise ratio between the fundamental and harmonic waves after correlation should be studied. If necessary, weighted compensation or consistency processing should be performed on the frequency-divided records before vertical stacking. This weighted compensation or consistency processing process is similar to the consistent amplitude compensation process in conventional seismic data processing.

[0158] (45) According to the conventional seismic data processing process, the heavy shots (collected simultaneously, there will be heavy shot records at the same time, for example, the first scanning frequency ω-2ω, its second-order harmonic is 2ω-4ω, and the second synchronous scanning frequency 2ω-4ω produces heavy shots.) are separated by multi-domain denoising to obtain the vibroseis-related post-seismic records of all shot points without harmonic interference. This step is implemented using existing technology and will not be repeated here.

[0159] The present invention provides a method for designing scanning signals for efficient seismic acquisition using a vibroseis system, which has the following advantages:

[0160] Through the bandwidth design of the synthetic scanning signal in step 1 and the data clipping and single-shot reconstruction in step 3, firstly, the separated harmonics are converted into effective signals, which reduces harmonic interference to a certain extent; secondly, the bandwidth of high-order harmonics is usually larger than that of the fundamental scanning signal. When the harmonics are converted into effective signals, the scanning bandwidth is also relatively expanded; thirdly, in step 3, the present invention adopts an independent synchronous scanning method to achieve efficient acquisition, which shortens the operation time and improves the operation efficiency compared with the traditional AS method.

[0161] The present invention also provides a vibroseis efficient scanning system based on harmonic frequency doubling characteristics, and the embodiments of the system are as follows:

[0162] [Example 2]

[0163] The system comprises:

[0164] Bandwidth design unit: used to design the bandwidth of the synthetic scanning signal;

[0165] Duration design unit: used to design the segmented scanning duration;

[0166] Acquisition unit: used to collect continuous relevant pre-scan data of all earthquake source points obtained during field construction;

[0167] Processing unit: connected to the acquisition unit, used to perform data clipping and single-shot reconstruction on the pre-correlation data to obtain the post-correlation seismic records.

[0168] The present invention also provides a computer-readable storage medium, and embodiments of the computer-readable storage medium are as follows:

[0169] [Example 3]

[0170] The computer-readable storage medium stores at least one computer-executable program, and when the at least one program is executed by the computer, the computer executes the steps of the above-mentioned controllable vibroseis efficient scanning method based on harmonic frequency multiplication characteristics.

[0171] The theoretical basis of the present invention is based on the cross-correlation characteristics of the scanning signal and the frequency doubling characteristics of the harmonic signal. The design adopts the frequency doubling independent synchronous scanning method (FDISS) to convert harmonic distortion into effective signals, eliminate harmonic interference, expand the effective bandwidth, and at the same time meet the technical requirements of independent synchronous scanning and improve operational efficiency. In theory, it can effectively solve the three problems faced by controllable source acquisition, and numerical simulation has achieved good results.

[0172] The present invention provides a basis for the transformation of seismic source equipment. To address the problem that existing vibrators cannot perform long sweeps in the low- and high-frequency bands, the first approach is to develop low- and high-frequency vibrators to improve their mechanical properties and make them more adaptable. The second approach is to develop harmonic vibrators and use harmonics to expand the sweep bandwidth. Furthermore, the present invention is simple to construct in the field and is applicable to all areas where vibrators can be used. The present invention requires the field collection and recording of relevant pre-correlation data, which is more conducive to denoising.

[0173] In response to certain shortcomings of existing vibroseis scanning methods, the present invention proposes a vibroseis scanning method based on harmonic frequency multiplication characteristics. Theoretical research and forward simulation data have shown that this scanning method has the following advantages:

[0174] ①Can be applied to independent synchronous scanning;

[0175] ② No harmonics are generated, or the harmonics are valid signals;

[0176] ③It can effectively broaden the excitation bandwidth and improve the wavelet resolution;

[0177] ④ It is applicable to the technical requirements of existing types of controllable vibrators, or can meet the technical requirements through limited technical transformation. The present invention uses the frequency doubling characteristics of harmonics and adopts a frequency doubling scanning method. Through the cutting, separation and reconstruction of single shots, the harmonics are made part of the effective signal, eliminating harmonic interference, expanding the scanning bandwidth, and improving operation efficiency;

[0178] ⑤Apply to relevant previous data;

[0179] ⑥ Provides a technical basis for the research and development and transformation of seismic source equipment.

[0180] The field operation of the scanning method of the present invention is the same as that of ISS, and its production efficiency can theoretically reach the level of ISS, and the data signal-to-noise ratio is equivalent to that of alternating scanning.

[0181] Finally, it should be noted that the above technical solution is only one embodiment of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the application methods and principles disclosed in the present invention, and it is not limited to the method described in the above specific embodiment of the present invention. Therefore, the method described above is only preferred and does not have a restrictive meaning.

Claims

1. A vibroseis efficient scanning method based on harmonic frequency multiplication characteristics, characterized by: The method utilizes the frequency doubling characteristics of harmonics and converts harmonics into effective signals through frequency doubling scanning, thereby expanding the effective bandwidth of the earthquake source and improving the resolution of the seismic wavelet; The method comprises: Step 1: Design the bandwidth of the synthetic sweep signal; Step 2: Design the segment scanning duration; Step 3: Conduct field construction to obtain continuous relevant pre-scan data of all shot points; Step 4: Perform data trimming and single-shot reconstruction on the pre-correlation data to obtain the post-correlation seismic records; The operation of step 1 includes: The bandwidth of the synthetic scanning signal is the difference between the cutoff frequency and the starting frequency of the scanning signal; The cutoff frequency is 2 to the power of the starting frequency; The operation of step 1 further includes: From the starting frequency to the cutoff frequency, the frequency is divided into N scanning segments; The cutoff frequency of each scanning segment is a multiple of the starting frequency, and the difference between the cutoff frequency and the starting frequency is the scanning bandwidth of the scanning segment; The data clipping operation in step 4 includes: (41) Sort the relevant front data according to the scanning bandwidth and scanning duration of each scanning segment; (42) The scanning time of each scanning segment plus the listening time is used as the clipping time, and the relevant front data is clipped using the clipping time to form the relevant front single shot; The single shot reconstruction operation in step 4 includes: (43) Perform correlation calculation on the pre-correlation single shot to form a post-correlation record; (44) Reconstruct the relevant post-records according to the positions of each shot point to obtain the relevant post-seismic records corresponding to each shot point; (45) The heavy guns were separated to obtain the vibroseis-correlated post-seismic records of all gun points without harmonic interference.

2. The vibroseis efficient scanning method based on harmonic frequency multiplication characteristics according to claim 1, characterized in that: The operation of step 2 includes: The duration of the long linear scan is evenly distributed according to the scan segments to obtain the scan duration of each scan segment.

3. The vibroseis efficient scanning method based on harmonic frequency multiplication characteristics according to claim 1, characterized in that: The operation of step 3 includes: At the designed shot point position, scan randomly according to the scan bandwidth and scan duration of each scan segment, and continuously record the relevant previous data; Each shot point position is scanned N times.

4. A vibroseis efficient scanning system based on harmonic frequency multiplication characteristics, for implementing the method according to any one of claims 1 to 3, characterized in that: The system comprises: Bandwidth design unit: used to design the bandwidth of the synthetic scanning signal; Duration design unit: used to design the segmented scanning duration; Acquisition unit: used to collect continuous relevant pre-data of all shot point segmented scanning obtained during field construction; Processing unit: connected to the acquisition unit, used to perform data clipping and single-shot reconstruction on the pre-correlation data to obtain the post-correlation seismic records.

5. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores at least one computer-executable program, and when the at least one program is executed by the computer, the computer executes the steps of the controllable vibrator efficient scanning method based on harmonic frequency multiplication characteristics as described in any one of claims 1 to 3.

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