Marine low frequency airgun source design method and airgun source

Abstract

The application provides a marine low-frequency air gun source design method and an air gun source. The method comprises the following steps: through subarray, array delay excitation design, reasonable delay excitation time is controlled, time domain source ghost wave is delayed relative to the main pulse, and the delay is increased, so that the purpose of increasing the low-frequency end energy and expanding the low frequency in the frequency domain is achieved. Through the design of the air gun source excitation method of the subarray delay excitation, the low-frequency energy proportion of the excitation wavelet can be effectively improved, the low-frequency expansion can be realized, and the applicability of the source wavelet in the medium-deep exploration field can be improved.

Description

Technical Field

[0001] This invention relates to the fields of computer-aided design and seismic exploration equipment, and particularly to a design method for a marine low-frequency air gun source based on subarray delay excitation and the air gun source. Background Technology

[0002] Currently, commonly used air gun seismic source arrays at sea consist of multiple single guns of different capacities and multiple sets of coherent guns of different capacities combined at the same immersion depth. Multiple air gun units achieve co-directional superposition of the initial waves through tuning, thus forming a high-energy main pulse signal. When the main pulse propagates through the water to the sea surface, its polarity reverses, forming a source ghost wave accompanying the main pulse. The presence of the source ghost wave causes a notch effect in the frequency domain, affecting certain mid-to-high frequency bands and low frequency bands. Currently, marine exploration aims to obtain richer low-frequency and ultra-low-frequency (below 6Hz) signals from excitation sources. This is achieved by sinking the source as deep as possible, thus increasing the ghost wave's delay relative to the main pulse and bringing the notch closer to the low-frequency end in the frequency domain, thereby enhancing low-frequency energy. Furthermore, existing technologies utilize the influence of different sinking depths on far-field wavelets, achieving ghost wave suppression through the superposition of main pulses from multiple sources (i.e., through depth combinations of multiple sources), thus suppressing ghost wave notches in the frequency domain and achieving broadband performance. However, all of these existing technologies have a significant problem: due to operational limitations, deeper sinking is not achievable (generally, sinking depth is within 9m). Moreover, deeper sinking results in more pronounced bubble oscillations, a larger bubble ratio, and poorer wavelet performance.

[0003] Therefore, how to improve the energy at the low-frequency end and expand the low-frequency range has become an urgent problem to be solved in order to enhance the source detection capability and achieve more accurate detection at sea. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a design method and source for a low-frequency marine airgun based on subarray delay excitation, which solves or at least partially solves the aforementioned problems. Specifically, this invention discloses the following technical solutions:

[0005] On one hand, the present invention provides a method for designing a low-frequency air gun source for marine applications, the method comprising:

[0006] S1. One or more sub-source arrays are set up together with the main source array;

[0007] S2. Calculate the propagation time of the main pulse and the source ghost wave generated by the main source array, and calculate the source ghost wave time difference between the two.

[0008] S3. Obtain the relationship between the source ghost wave and the source ghost wave time difference;

[0009] S4. The time difference between the excitation time of the sub-source array and the excitation time of the main source array is equal to the source ghost wave time difference.

[0010] Preferably, in S2: the main pulse propagation time is:

[0011] The propagation time of the ghost wave from the epicenter is:

[0012] The time difference of the ghost wave at the epicenter is: Δt = t sghost -t real ,

[0013] Where v represents the speed of seismic waves in seawater, and h represents the depth of the strata. s h represents the focal depth. r denoted by the detector depth, and x represents the lateral shot-detector distance.

[0014] Preferably, when there is only one sub-source array, the excitation delay time of the sub-source array is equal to the source ghost wave time difference of the main source array;

[0015] When there are multiple sub-source arrays, the excitation delay time of the subsequent sub-source array is equal to the source ghost wave time difference of the preceding sub-source array.

[0016] More preferably, the calculation method for the source ghost wave time difference of the sub-source array can be the same as the calculation method for the source ghost wave time difference of the main source array.

[0017] Preferably, when there is only one sub-source array, the source array design ensures that the amplitude of the main pulse of the sub-source array is consistent with that of the source ghost wave of the main source array, but with opposite polarities.

[0018] When there are multiple sub-source arrays: through source array design, the main pulse of the first-level sub-source array is made to have the same amplitude as the source ghost wave of the main source array, but with opposite polarities; the main pulse of the next-level sub-source array is made to have the same amplitude as the source ghost wave of the previous-level sub-source array, but with opposite polarities.

[0019] Preferably, in the source array design, the amplitude matching relationship between the main source array and the sub-source array, and between the sub-source array and the next-level sub-source array, satisfies the following:

[0020] |A′ i ghost| =|A i+1 real |

[0021] A′ i ghost =K Ai real +L Ai real

[0022] Among them, A′ i ghostLet A be the ghost wave amplitude of the i-th source array. i real A i+1 real , respectively, are the main pulse amplitudes of the i-th and i+1-th level source arrays, K is the empirical constant of the negative pulse amplitude; L is the sea surface reflection coefficient; 0 << i << N, i = 0 represents the main source array; N represents the total number of main source arrays and sub-source arrays.

[0023] Preferred, A real =CV1 / 3, where A real 1 is the main pulse amplitude; C is an empirical constant, which is related to the immersion depth and working pressure; V is the air gun capacity.

[0024] Preferably, in step S3, the relationship between the notch frequency of the source ghost wave and the time difference of the source ghost wave is as follows:

[0025]

[0026] Where Δt represents the ghost wave time difference at the source, θ is the incident angle of the wavelet, and f n This represents the notch frequency of the ghost wave at the seismic source.

[0027] Preferably, when determining the relationship between the source ghost wave and the source ghost wave time difference, the zero offset case is adopted, that is, θ = 90°.

[0028] Furthermore, the present invention also provides a marine low-frequency air gun source, the source comprising:

[0029] A main source array for generating low-frequency sources; and one or more sub-source arrays located at the same depth as the main source.

[0030] When there is only one sub-source array, the excitation delay time of the sub-source array is equal to the source ghost wave time difference of the main source array;

[0031] When there are multiple sub-source arrays, the excitation delay time of the subsequent sub-source array is equal to the source ghost wave time difference of the preceding sub-source array.

[0032] Preferably, the method for calculating the source ghost wave time difference is as follows:

[0033] The propagation time of the main pulse is:

[0034] The propagation time of the ghost wave from the epicenter is:

[0035] The time difference of the ghost wave at the epicenter is: Δt = t sghost -t real ,

[0036] Where v represents the speed of seismic waves in seawater, and h represents the depth of the strata. sh represents the focal depth. r denoted by the detector depth, and x represents the lateral shot-detector distance.

[0037] Preferably, when there is only one sub-source array, the source array design ensures that the amplitude of the main pulse of the sub-source array is consistent with that of the source ghost wave of the main source array, but with opposite polarities.

[0038] When there are multiple sub-source arrays: through source array design, the main pulse of the first-level sub-source array is made to have the same amplitude as the source ghost wave of the main source array, but with opposite polarities; the main pulse of the next-level sub-source array is made to have the same amplitude as the source ghost wave of the previous-level sub-source array, but with opposite polarities.

[0039] Preferably, in the source array design, the amplitude matching relationship between the main source array and the sub-source array, and between the sub-source array and the next-level sub-source array, satisfies the following:

[0040] |A′ i ghost |=|A i+1 real |

[0041] A′ i ghost =KA i real +LA i real

[0042] Among them, A′ i ghost Let A be the ghost wave amplitude of the i-th source array. i real A i+1 real , respectively, are the main pulse amplitudes of the i-th and i+1-th level source arrays, K is the empirical constant of the negative pulse amplitude; L is the sea surface reflection coefficient; 0 << i << N, i = 0 represents the main source array; N represents the total number of main source arrays and sub-source arrays.

[0043] Preferred, A real =CV 1 / 3 In the formula, A real 1 is the main pulse amplitude; C is an empirical constant, which is related to the immersion depth and working pressure; V is the air gun capacity.

[0044] Preferably, when the total number of main source arrays and sub-source arrays is N, the notch frequency f of the source ghost wave is... x for:

[0045]

[0046] Among them, f n This represents the notch frequency of the ghost wave at the seismic source.

[0047] Preferably, the relationship between the notch frequency of the source ghost wave and the source ghost wave time difference is as follows:

[0048]

[0049] Where Δt represents the ghost wave time difference at the source, θ is the incident angle of the wavelet, and f n This represents the notch frequency of the ghost wave at the seismic source.

[0050] Preferably, when determining the relationship between the source ghost wave and the source ghost wave time difference, the zero offset case is adopted, that is, θ = 90°.

[0051] Compared with existing technologies, the solution provided by this invention, through array delay excitation design, controls a reasonable delay excitation time to increase the time-domain source ghost wave delay relative to the main pulse, thereby achieving the purpose of increasing low-frequency energy and low-frequency extension in the frequency domain. By extending the time difference between the main pulse and the ghost wave, the ghost wave phase is controllable, and the ghost wave trap position is moved to a lower frequency, achieving low-frequency enhancement. Through the design of the air gun source excitation method with subarray delay excitation, the proportion of low-frequency energy of the excitation wavelet can be effectively increased and low-frequency extension can be achieved, improving the applicability of the source wavelet in the field of medium-deep exploration. In this solution, the main source and auxiliary source are set at the same depth, which can effectively avoid the problem of source immersion depth setting. This solution can achieve the equivalent effect of source immersion depth of 10-30m without actual deep immersion, and avoids the problem of excessive hydrostatic pressure caused by excessive immersion affecting the source excitation performance. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 This is a schematic diagram of the far-field wavelet time domain according to an embodiment of the present invention;

[0054] Figure 2 This is a schematic diagram of the propagation path of the source main pulse and ghost wave in an embodiment of the present invention;

[0055] Figure 3 This is a schematic diagram of the far-field wavelet frequency domain according to an embodiment of the present invention;

[0056] Figure 4 This is a schematic diagram of the array delay excitation mode according to an embodiment of the present invention;

[0057] Figure 5 This is a schematic diagram of the array delay excitation time domain wavelet signal according to an embodiment of the present invention;

[0058] Figure 6 This is a schematic diagram comparing the frequency domain amplitude spectrum of array delay excitation according to an embodiment of the present invention;

[0059] Figure 7 This is a flowchart of a method according to an embodiment of the present invention. Detailed Implementation

[0060] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0061] Those skilled in the art should understand that the following specific embodiments or implementation methods are a series of optimized configurations listed to further explain the specific content of the invention. These configuration methods can be combined or used in conjunction with each other, unless the invention explicitly states that some or a specific embodiment or implementation method cannot be associated with or used in conjunction with other embodiments or implementation methods. Furthermore, the following specific embodiments or implementation methods are merely optimized configurations and are not intended to limit the scope of protection of the invention.

[0062] To address the shortcomings of existing technologies, this invention aims to employ computer-aided design methods to control a reasonable delay excitation time through array delay excitation design. This increases the time-domain ghost wave delay relative to the main pulse, thereby achieving improved low-frequency energy and low-frequency extension in the frequency domain. The invention's design of a gas gun source excitation method using subarray delay excitation effectively increases the proportion of low-frequency energy in the excitation wavelet and achieves low-frequency extension, enhancing the applicability of the source wavelet in medium-to-deep exploration.

[0063] In one specific embodiment, combined with Figure 7 As shown, the technical solution of the present invention can be implemented by the following method:

[0064] Figure 1 For a certain airgun array excited in the time domain far-field wavelet, the time difference between the source ghost wave and the main pulse is mainly affected by the source immersion depth, combined with Figure 2 As shown in Formulas 1, 2, and 3, the time difference between the source ghost wave and the main pulse is directly related to the source immersion depth. In this embodiment, the propagation time of the main pulse and the source ghost wave is obtained in the following way:

[0065] Main pulse propagation time: Ghost wave propagation time at the epicenter: Where v represents the speed of seismic waves in seawater, and h represents the depth of the strata. s h represents the focal depth.r denoted by the detector depth, and x represents the lateral shot-detector distance.

[0066] Ghost wave time difference at the epicenter: Δt = t sghost- t real Formula 3

[0067] Combination Figure 3 As shown, due to the influence of the source ghost wave, a significant frequency domain notch effect occurs. The notch frequency is directly related to the time difference of the source ghost wave. We need to further describe the relationship between the notch frequency and the time difference of the source wave, see Formula 4:

[0068]

[0069] Where θ is the incident angle of the wavelet, f n The notch frequency is the ghost wave frequency of the seismic source.

[0070] In this embodiment, we need to further consider the far-field wavelet performance. An excellent source array requires a high main pulse value of the far-field wavelet in the time domain, which means that it can excite sufficient source energy; the accompanying bubble pulse should be small, which means less interference; and the frequency domain far-field wavelet spectrum jitter should be small, indicating a smooth spectrum. In a preferred embodiment, we select the zero offset case, that is, below the vertical air gun, where θ = 90°. Then, Equation 4 can be approximated as the following Equation 5:

[0071]

[0072] In this embodiment, by delaying excitation using a subarray (or subarray array), the time difference Δt between the source ghost wave and the main pulse can be increased, thereby shifting the notch wave frequency to the lower frequency end. In the design of the subarray, different subarrays or subarray arrays can be used, as long as these arrays meet the design concept proposed in this invention, namely: through the combined design of subarrays or subarray arrays, the main pulse amplitude value of array A and the ghost wave amplitude value of array B can be kept consistent.

[0073] Combination Figure 4 As shown, based on the original source array A, another source array B is added, and the excitation time of array B is delayed by Δt compared with array A. i ( Figure 4 As shown), and Δt i This is equal to the time difference Δt between the source ghost wave and the main pulse. By utilizing the characteristic that the source ghost wave and the main pulse have the same amplitude but opposite polarity, the source ghost wave generated by array A and the main pulse generated by array B cancel each other out. The final signal contains only the main pulse of array A and the source ghost wave of array B, ultimately achieving the goal of a time difference of 2Δt between the main pulse and the source ghost wave. Figure 5 As shown, at this time, the notch frequency f i =fn / 2, thus shifting the notch filter frequency towards the lower frequency end, thereby increasing the energy proportion of the low-frequency band in the frequency domain, achieving the purpose of increasing low-frequency energy and extending the low-frequency range, and its amplitude is compared to, for example Figure 6 As shown.

[0074] Using the above-mentioned method, delayed excitation of arrays A, B, C...N (N≧2) can be achieved. Controlling the delayed excitation time of the Nth array to (N-1)Δt allows for a time difference of N times Δt between the main pulse and the source ghost wave, and a notch frequency f. x f n / N, the notch frequency is further shifted to the lower frequency end, thereby achieving the purpose of further improving the low-frequency energy and extending the low frequency range. Taking arrays B and C as examples, after array B is combined with array A with an appropriate delay time Δt, the main pulse of array B and the ghost wave of array A cancel each other out. The far-field wavelet signal contains the main pulse of array A and the ghost wave of array B, and the ghost wave time difference changes from Δt to 2Δt. By designing the source array, the main pulse amplitude of array C is made consistent with the ghost wave amplitude of array B. Array C has an additional excitation delay of 2Δt, and the main pulse of array C cancels out the ghost wave of array B. The far-field wavelet signal contains the main pulse of array A and the ghost wave of array C, and the ghost wave time difference changes from 2Δt to 3Δt. If other arrays D, array E, etc. are added, the settings of other arrays D, array E, etc. are the same as above, and will not be repeated here. The notch frequency of the ghost wave further decreases due to the increase in the ghost wave time difference, thereby achieving the purpose of shifting the notch frequency to the lower frequency end, improving the low-frequency energy and extending the low frequency range.

[0075] In yet another, more preferred embodiment, the amplitude matching between the main source and the auxiliary source can be calculated in the following way:

[0076] The calculation method for the far-field wavelet master pulse of the source array is relatively complex. Based on the free bubble oscillation theory and combined with the gun array tuning theory, we obtained a simulation algorithm for the excitation energy intensity of the gun array. Furthermore, it can be corrected based on the actual test parameters.

[0077] First, ① calculate the main pulse value of the main source. The amplitude of the main pulse of the far-field wavelet is proportional to the cube root of the air gun capacity:

[0078] A real =CV 1 / 3

[0079] In the formula, A real 1 is the main pulse amplitude; C is an empirical constant, which is related to the immersion depth and working pressure; V is the air gun capacity.

[0080] ② Based on the sea state of the target area, select a reasonable sea surface reflection coefficient and calculate the ghost wave pulse value of the main source. The negative pulse of bubble oscillation is directly proportional to the main pulse:

[0081] A nega =KA real

[0082] In the formula, A nega A represents the negative pulse amplitude. real The main pulse amplitude is K; K is an empirical constant.

[0083] The source ghost wave is a signal with opposite polarity to the first wave, formed after the first wave signal is reflected from the sea surface. The intensity of the source ghost wave pulse is expressed as:

[0084] A ghost =LA real

[0085] In the formula, A ghost A represents the amplitude of the ghost wave at the epicenter; real The main pulse amplitude is L; the sea surface reflection coefficient is usually -1 in theory, but in reality, the sea surface reflection coefficient is related to the roughness of the sea surface. For example, in sea conditions of level 3 wind and waves, the sea surface reflection coefficient is usually taken as -0.85. In this embodiment, the sea surface reflection coefficient is based on the actual test site coefficient.

[0086] ③ Based on the main pulse and ghost pulse values, calculate the actual ghost pulse magnitude of the far-field wavelet of the main source. The far-field wavelet of the source is the result of adding the first wave signal and the source ghost wave signal in the time domain, that is, the actual ghost pulse magnitude of the far-field wavelet signal is:

[0087] A' ghost =A nega +A ghost

[0088] In the formula, A' ghost A represents the amplitude of the far-field sub-wave ghost wave; ghost A represents the amplitude of the ghost wave at the epicenter; nega It represents the amplitude of a negative pulse.

[0089] ④ Through a reasonable gun array combination design, an auxiliary seismic source (which may be the same as or different from the main seismic source) is designed to ensure that the magnitude of the main pulse of the auxiliary seismic source and the ghost pulse of the main seismic source remain consistent at the same immersion depth. By using a reasonable time-delay excitation, the time difference of the ghost pulse of the main seismic source is increased, while ensuring that the interference signal level is minimized. The design of the time-delay excitation has been described above and will not be repeated here.

[0090] Based on the above settings, taking the main source and the first-order sub-source as an example, to achieve the above objective, the far-field wavelet ghost wave amplitude can be expressed as:

[0091] A′ ghost =KA real +LA real

[0092] Where A′ ghost A represents the amplitude of the far-field sub-wave ghost wave; real The main pulse amplitude is denoted by K, which is an empirical constant for the negative pulse amplitude and is related to the immersion depth and working pressure. The sea surface reflection coefficient is related to the roughness of the sea surface.

[0093] When matching the amplitude between the main source and the first-order sub-source, the following relationship must be satisfied:

[0094] |A0' ghost |=|A 1real |

[0095] Where A0' ghost The amplitude of the ghost wave, a wavelet in the far field from the main seismic source, is A. 1real The amplitude of the main pulse of the first sub-source; main source A0' ghost The solution method and A' ghost The same applies. The amplitude of the main pulse of the second-level sub-source and the amplitude of the ghost wave of the far-field wavelet of the first-level sub-source must also satisfy the above formula, and so on, without further explanation.

[0096] The key to this embodiment is to match the main pulse of the auxiliary source with the actual ghost wave pulse of the auxiliary source in terms of both time and amplitude, so as to achieve the best matching effect and minimize the level of interference signal.

[0097] ⑤ If the next-level auxiliary source is considered, the amplitude of the main pulse of the next-level auxiliary source (i.e., the second-level sub-source) should be consistent with that of the ghost wave of the first-level auxiliary source.

[0098] In yet another specific embodiment, the present invention also provides a marine low-frequency airgun source based on subarray delay excitation, the source comprising:

[0099] A main source array for generating low-frequency sources; and one or more sub-source arrays;

[0100] When there is only one sub-source array, the excitation delay time of the sub-source array is equal to the source ghost wave time difference of the main source array;

[0101] When there are multiple sub-source arrays, the excitation delay time of the subsequent sub-source array is equal to the source ghost wave time difference of the preceding sub-source array.

[0102] Preferably, the method for calculating the source ghost wave time difference is as follows:

[0103] The propagation time of the main pulse is:

[0104] The propagation time of the ghost wave from the epicenter is:

[0105] The time difference of the ghost wave at the epicenter is: Δt = t sghost -t real ,

[0106] Where v represents the speed of seismic waves in seawater, and h represents the depth of the strata. s h represents the focal depth. r denoted by the detector depth, and x represents the lateral shot-detector distance.

[0107] Preferably, when there is only one sub-source array, the main pulse of the sub-source array has the same amplitude as the source ghost wave of the main source array, but with opposite polarities.

[0108] When there are multiple sub-source arrays: the main pulse of the first-level sub-source array has the same amplitude as the source ghost wave of the main source array, but opposite polarity; the main pulse of the next-level sub-source array has the same amplitude as the source ghost wave of the previous-level sub-source array, but opposite polarity.

[0109] Preferably, when the total number of main source arrays and sub-source arrays is N, the notch frequency f x for:

[0110]

[0111] Among them, f n This represents the notch frequency of the ghost wave at the seismic source.

[0112] Preferably, in the source array design, the amplitude matching relationships between the main source and the sub-sources, and between the sub-sources and the next-level sub-sources, satisfy the following:

[0113] |A′ ighost |=|A i+1real |

[0114] A′ ighost =KA ireal +LA ireal

[0115] Among them, A′ i ghost Let A be the ghost wave amplitude of the i-th source. i real A i+1 real , where are the main pulse amplitudes of the i-th and i+1-th level sources, respectively; K is the empirical constant for negative pulse amplitude; L is the sea surface reflection coefficient; 0 << i << N, where i = 0 represents the main source; N represents the total number of main sources and sub-sources.

[0116] Preferred, A real =CV 1 / 3In the formula, A real 1 is the main pulse amplitude; C is an empirical constant, which is related to the immersion depth and working pressure; V is the air gun capacity.

[0117] Preferably, the relationship between the source ghost wave and the source ghost wave time difference is as follows:

[0118]

[0119] Where Δt represents the ghost wave time difference at the source, θ is the incident angle of the wavelet, and f n This represents the notch frequency of the ghost wave at the seismic source.

[0120] Preferably, when determining the relationship between the source ghost wave and the source ghost wave time difference, the zero offset case is adopted, that is, θ = 90°.

[0121] In another embodiment, the design method of the present invention can also be implemented by means of a device, which may include one or more processors and a memory.

[0122] The processor can be a central processing unit (CPU) or other form of processing unit with data processing and / or information execution capabilities, and can control other components in the device to perform the desired functions.

[0123] The memory may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may include, for example, random access memory (RAM) and / or cache memory. The non-volatile memory may include, for example, read-only memory (ROM), hard disk, flash memory, etc. One or more computer program information may be stored on the computer-readable storage medium, and the processor may run the program information to implement the subarray delay-excited marine low-frequency seismic source design method of the various embodiments of the present invention described above, or other desired functions.

[0124] In one example, the device may also include input and output devices, which are interconnected via a bus system and / or other forms of connection (not shown). The input device may include, for example, a keyboard, mouse, etc. The output device may output various information to the outside. The output device may include, for example, a display, a communication network, and its connected remote output devices, etc. In addition, depending on the specific application, the device may include any other suitable components.

[0125] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of this solution includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which the embodiments of this solution pertain. The processor performs the various methods and processes described above. For example, the method embodiments of this solution can be implemented as software programs tangibly contained in a machine-readable medium, such as memory. In some embodiments, part or all of the software program can be loaded and / or installed via memory and / or a communication interface. When the software program is loaded into memory and executed by the processor, one or more steps of the methods described above can be performed. Alternatively, in other embodiments, the processor can be configured to perform one of the methods described above by any other suitable means (e.g., by means of firmware).

[0126] The logic and / or steps represented in the flowchart or otherwise described herein may be specifically implemented in any readable storage medium for use by, or in conjunction with, an instruction execution system, apparatus or device (such as a computer-based system, a processor-included system or other system that can fetch and execute instructions from, an instruction execution system, apparatus or device).

[0127] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for designing a low-frequency air gun source for marine applications, characterized in that: The method includes: S1. The low-frequency air gun source includes a main source array and one or more sub-source arrays located at the same depth as the main source array; the gun array design of the main source array and the sub-source arrays ensures that the magnitude of the main pulse of the sub-source array and the ghost pulse of the main source array are consistent at the same immersion depth. S2. Calculate the propagation time of the main pulse and the source ghost wave generated by the main source array, and calculate the source ghost wave time difference between the two. S3. Obtain the relationship between the source ghost wave and the source ghost wave time difference; S4. The time difference between the excitation time of the sub-source array and the excitation time of the main source array is equal to the source ghost wave time difference. When there is only one sub-source array, the excitation delay time of the sub-source array is equal to the source ghost wave time difference of the main source array; When there are multiple sub-source arrays, the excitation delay time of the subsequent sub-source array is equal to the source ghost wave time difference of the preceding sub-source array. The method for calculating the source ghost wave time difference of the sub-source array is as follows: The propagation time of the main pulse is: , The propagation time of the ghost wave at the epicenter is: , The time difference of the ghost wave at the epicenter is: , Where v represents the speed of seismic waves in seawater, and h represents the depth of the strata. s h represents the focal depth. r denoted by detector depth, x represents the lateral shot-detector distance; When there is only one sub-source array, the main pulse of the sub-source array is designed to have the same amplitude and opposite polarity as the source ghost wave of the main source array. When there are multiple sub-source arrays: through source array design, the main pulse of the first-level sub-source array is made to have the same amplitude as the source ghost wave of the main source array, but with opposite polarities; the main pulse of the next-level sub-source array is made to have the same amplitude as the source ghost wave of the previous-level sub-source array, but with opposite polarities. In the design of seismic source arrays, the amplitude matching relationships between the main source array and the sub-source arrays, and between the sub-source arrays and the next-level sub-source arrays, satisfy the following: in, Let be the ghost wave amplitude of the i-th source array. , , respectively, are the main pulse amplitudes of the i-th and i+1-th level source arrays, K is the empirical constant of the negative pulse amplitude; L is the sea surface reflection coefficient; When i=0, it represents the main source; N represents the total number of main source arrays and sub-source arrays.

2. The method according to claim 1, characterized in that, In S3, the relationship between the notch frequency of the source ghost wave and the source ghost wave time difference is as follows: in, The time difference of the ghost wave at the earthquake source is represented by θ, where θ is the incident angle of the wavelet. This represents the notch frequency of the ghost wave at the seismic source.

3. A low-frequency air gun source for marine applications, characterized in that: The low-frequency air gun source includes: The main source array, and one or more sub-source arrays at the same depth as the main source array; the gun array design of the main source array and the sub-source arrays ensures that the magnitude of the main pulse of the sub-source array and the ghost pulse of the main source array are consistent at the same immersion depth. When there is only one sub-source array, the excitation delay time of the sub-source array is equal to the source ghost wave time difference of the main source array; When there are multiple sub-source arrays, the excitation delay time of the subsequent sub-source array is equal to the source ghost wave time difference of the preceding sub-source array. The method for calculating the ghost wave time difference at the seismic source is as follows: The propagation time of the main pulse is: , The propagation time of the ghost wave at the epicenter is: , The time difference of the ghost wave at the epicenter is: , Where v represents the speed of seismic waves in seawater, and h represents the depth of the strata. s h represents the focal depth. r denoted by detector depth, x represents the lateral shot-detector distance; When there is only one sub-source array, the main pulse of the sub-source array is designed to have the same amplitude and opposite polarity as the source ghost wave of the main source array. When there are multiple sub-source arrays: through source array design, the main pulse of the first-level sub-source array is made to have the same amplitude as the source ghost wave of the main source array, but with opposite polarities; the main pulse of the next-level sub-source array is made to have the same amplitude as the source ghost wave of the previous-level sub-source array, but with opposite polarities. In the aforementioned source array design, the amplitude matching relationships between the main source array and the sub-source array, and between the sub-source array and the next-level sub-source array, satisfy the following: in, Let be the ghost wave amplitude of the i-th source array. , , respectively, are the main pulse amplitudes of the i-th and i+1-th level source arrays, K is the empirical constant of the negative pulse amplitude; L is the sea surface reflection coefficient; When i=0, it represents the main source array; N represents the total number of main source arrays and sub-source arrays.

Images