Method and application of stereoscopic arrangement and delayed excitation to broaden the frequency band of airgun source wavelet

Abstract

This invention belongs to the field of airgun source technology in shallow sea seismic exploration, and discloses a method and application for widening the frequency band of airgun source wavelets through three-dimensional arrangement and delayed excitation. By calculating the immersion depth of airguns of different capacities and the time to reach the peak value of the main pulse after excitation, and then adjusting the immersion depth and excitation time of airguns of different capacities based on the calculated time, the time shift corresponding to the peak value of the main pulse of each airgun of different capacities in the airgun array is achieved. This ultimately constructs a narrower main pulse waveform for the airgun array's sharp pulse source wavelet, thus widening the frequency band of the source wavelet. By adjusting the immersion depth and excitation time of airguns of different capacities to construct sharp pulse wavelets and suppressing virtual reflections, this invention achieves the goal of extending the frequency band of the airgun array to lower frequencies while maintaining high frequencies, ultimately obtaining an airgun source with rich high and low frequency frequencies and strong energy transmission capability for mid-to-deep geological targets.

Description

Technical Field

[0001] This invention belongs to the field of air gun source technology in shallow sea seismic exploration, and particularly relates to the method and application of three-dimensional arrangement and delayed excitation to broaden the wavelet frequency band of air gun source. Background Technology

[0002] In marine geological surveys and oil and gas resource exploration, airgun seismic sources are key equipment in marine seismic information acquisition systems. Especially compared to other sources, the low-frequency energy of airgun seismic sources is more suitable for exploring geological targets in the middle and deep seas. As marine oil and gas resource exploitation moves towards the middle and deep layers, geological conditions become increasingly complex, and the requirements for seismic acquisition accuracy and resolution increase accordingly. Therefore, airgun seismic sources rich in low-frequency energy are receiving increasing attention. High-capacity airguns can contribute more low-frequency signals, but the bubble effect is significant.

[0003] Currently, both domestically and internationally, the main approach is to broaden the source wavelet bandwidth and improve the downlink capability of seismic waves in seismic exploration through multi-subarray planar and three-dimensional combinations, utilizing tuning and coherence techniques. However, while high-frequency components are often enhanced, low-frequency components are not enriched. Therefore, how to generate source wavelets with stronger low-frequency energy is a pressing problem in the field of geophysics. Enriching the low-frequency components and improving the penetration capability of the airgun source wavelet is the focus of this invention, based on existing technologies.

[0004] Based on the above analysis, the problems and shortcomings of the existing technology are as follows:

[0005] (1) The existing technology does not construct sharp pulse wavelets by setting the immersion depth of air guns of different capacities and adjusting the excitation time of air guns of different capacities, and cannot generate source wavelets with high resolution and high penetration capability suitable for exploration of geological targets in shallow seas and deep layers.

[0006] (2) Existing technologies cannot broaden the frequency band of the seismic source wavelet, resulting in poor detection of deep geological targets. Summary of the Invention

[0007] To overcome the problems existing in related technologies, the present invention discloses an embodiment of a method for broadening the wavelet frequency band of an air gun source by three-dimensional arrangement and delayed excitation, which is used in a broadband high-resolution three-dimensional observation system in the marine field to explore and collect mid-to-deep seismic reflection signals and to use them for marine geological surveys and oil and gas resource exploration.

[0008] The purpose of this invention is to construct sharp pulse wavelets by setting the immersion depth of air guns with different capacities and adjusting the excitation time of air guns with different capacities, and finally generate source wavelets with high resolution and high penetration capability suitable for exploration of geological targets in shallow and deep seas.

[0009] The technical solution is as follows: A method for broadening the frequency band of the air gun source wavelet through three-dimensional arrangement and delayed excitation involves calculating the immersion depth of air guns of different capacities and the time it takes for the air gun to reach the peak value of the main pulse after excitation. Then, based on the calculated time, the immersion depth of air guns of different capacities is adjusted, and the excitation time of these air guns is simultaneously adjusted, causing a time shift corresponding to the peak value of the main pulse of each air gun of different capacities in the air gun array. Finally, a narrow, sharp pulse source wavelet with a narrow main pulse waveform is constructed for the air gun array, thus achieving the broadening of the source wavelet frequency band. Specifically, the following steps are included:

[0010] S1. Simulate gas gun wavelets of different capacities based on the van der Waals nonideal gas gas gun wavelet model and set initial conditions.

[0011] S2. Execute the simulation process according to the initial conditions set in step S1;

[0012] S3. Analyze the simulated air gun wavelets and statistically analyze the time t from excitation to the peak value of the main pulse for air gun wavelets of different capacities. i ;

[0013] S4. According to the simulation results, the smaller the capacity t i The smaller the value, the less likely it is to be the minimum value t. i Let t0 be the time difference between Δt and t0 for different capacity air guns from excitation to reaching the peak of the main pulse. i , Δt i =t i -t0;

[0014] S5. Take 1 / 2Δt calculated in step S4. i As a delay firing time for air guns of different capacities in the air gun array, the immersion depth of this part of the air guns is reduced by 1 / 4Δt. i •C, where C is the gas velocity, followed by air gun wavelet simulation;

[0015] S6. Perform spectral analysis on the air gun array wavelet obtained in step S5.

[0016] In step S1, the equations of the van der Waals nonideal gas gun wavelet model are expressed as follows:

[0017]

[0018] In the formula, a and b are both van der Waals constants, and a = 0.1404m. 6 ·Pa·mol -2 b = 3.764 × 10 -5 m 3 ·mol -1 T g For the effective thermodynamic temperature, R g m is the universal gas constant. gV is the mass of the gas. g For volume;

[0019] Effective temperature T g Depends on the high-pressure gas in the chamber:

[0020] T g =T w (1+P g / P c (2)

[0021] In the formula, P c =139MPa;

[0022] During the air gun firing process, according to the law of conservation of energy, the energy gained from heat transfer and mass transfer of the bubble must be balanced with the change in the bubble's internal energy. Therefore:

[0023]

[0024] In the formula, T is the bubble temperature, P is the bubble pressure, and m b It is the mass of the gas inside the bubble, U=C m m b T represents the internal energy of the bubble, C m dQ / dt is the specific heat capacity at constant pressure, dQ / dt is the heat transfer rate through the bubble wall, the heat transfer coefficient k is determined by fitting the model with experimental data, and the bubble heat loss rate is expressed as:

[0025]

[0026] In the formula, ΔT=T b -T w It is the bubble temperature T b and the surrounding water temperature T w The temperature difference between them, where R is the bubble radius; using the van der Waals nonideal gas equation, the internal energy of a nonideal gas is a function of its temperature and volume:

[0027]

[0028] The total differential equation is expressed as:

[0029]

[0030] The first law of thermodynamics is transformed into:

[0031]

[0032] In the formula, R g =C m -C m ; rate of change of the amount of gaseous substance Throttling constant τ, Vg It is the air chamber volume, m g It is the amount of gas in the chamber, P g It's the air gun pressure, P b It is bubble pressure;

[0033] The throttling constant of air guns with different capacities depends only on the size of the air chamber; according to the power law, it can be expressed as:

[0034]

[0035] In the formula, τ0 is the port throttling constant independent of capacity, and ζ is the throttling power law exponent determined by comparison with measured data. According to the measurement and calculation results, the gas flow rate through the air gun port depends on the pressure difference inside and outside the air gun at any given time, and the gas release rate is expressed as:

[0036]

[0037] In the formula, m b It is the amount of gaseous substance released into the bubble, m g | t＝0 It is the total amount of gas in the chamber, and η is the ratio of the amount of gas in the bubble to the total amount;

[0038] The equation of motion for the bubble wall is expressed as:

[0039]

[0040] In the formula, R is the bubble radius, and u and These are the velocity and acceleration of the bubble wall, respectively, and c is the velocity of the sound wave in the fluid medium. It is the enthalpy difference of the bubble wall, ρ ∞ It is the still water density at infinity, P b It is the bubble pressure, P ∞ It is the hydrostatic pressure at infinity; the hydrostatic pressure of the bubble changes as the bubble rises due to buoyancy, and the expression for the vertical rising velocity of the bubble during the rising process is:

[0041]

[0042] In the formula, z is the bubble depth, g is the gravitational acceleration constant, R is the bubble radius, and P is the hydrostatic pressure. ∞ The expression is:

[0043]

[0044] In the formula, P atm It is standard atmospheric pressure, z g It's the depth of the air gun;

[0045] At a distance of 1m from the air gun, the air gun wavelet signal is represented as:

[0046]

[0047] At low frequencies, the interaction between bubbles cannot be ignored; this interaction between bubbles regulates the hydrostatic pressure of the fluid; the interaction between bubbles causes changes in the pressure around the bubbles; relative to the seismic wavelength, a bubble is a point, and the pressure field around any bubble is the superposition of the hydrostatic pressure and the time-varying pressure field generated by the bubble; the effective hydrostatic pressure at the i-th bubble is:

[0048]

[0049] In the formula, P ∞ It is hydrostatic pressure, ∑ k≠i ΔP ik It is the sum of the pressure contributions of all other air guns in the air gun array, ΔP ik It consists of the hydrostatic pressure disturbance on the i-th bubble caused by the k-th bubble, and the time delay and pressure characteristics on the i-th bubble caused by the k-th bubble:

[0050]

[0051] In the formula, r ik This represents the distance between the i-th bubble and the k-th bubble.

[0052] In step S1, the initial conditions specifically include:

[0053] Step 1.1, Condition 1: Set the initial value P of the air gun pressure. g | t＝0 Set to working pressure;

[0054] Step 1.2, Condition 2: The initial temperature inside the bubble is set to T. g =T w (1+P g / P c );

[0055] Step 1.3, Condition 3: Initial volume V of the bubble b | t＝0 =V g The initial radius is

[0056] Step 1.4, Condition 4: The initial velocity of the bubble wall is u = 0;

[0057] Step 1.5, Condition 5: Initial pressure P of the bubble b | t＝0 =P ∞ The initial temperature is water temperature T.w =18°, the initial mass of the substance inside the bubble is

[0058] Step 1.6, Condition 6: Set the placement position (x, y, z) of each air gun.

[0059] In step S2, the simulation process is executed according to the initial conditions set in step S1, specifically as follows:

[0060] Step 2.1: Input the initial conditions for the van der Waals nonideal gas gun wavelet model;

[0061] Step 2.2: Start the time loop and calculate the bubble volume at time t = k.

[0062] Step 2.3: Calculate the bubble pressure P at time t = k using equation (1). b ;

[0063] Step 2.4: Calculate the bubble heat loss rate using equation (4).

[0064] Step 2.5: Calculate the gas release rate using equation (9).

[0065] Step 2.6: Calculate the rate of change of bubble volume at time t = k.

[0066] Step 2.7: Calculate the rate of temperature change inside the bubble at time t = k using equation (7).

[0067] Step 2.8: Calculate the enthalpy difference of the bubble wall.

[0068] Step 2.9: Obtain the rate of change of bubble pressure by differentiating equation (1) with respect to time t.

[0069] Step 2.10: Differentiate the enthalpy difference with respect to time t to obtain...

[0070] Step 2.11: Calculate the rate of change of the bubble wall velocity at time t = k using equation (10). The acceleration of the bubble wall;

[0071] Step 2.12, for Find the derivative with respect to time t to obtain...

[0072] Step 2.13: Since the air gun wavelet simulation is an iterative process, the bubble wall radius, bubble wall velocity, gas temperature, and mass of the gas inside the bubble can be obtained through second-order Taylor series expansion.

[0073] and

[0074] Step 2.14: Express the bubble pressure as a function of enthalpy, bubble wall velocity, and bubble radius: R0 is the distance from the bubble center to the far-field point;

[0075] Step 2.15: Repeat steps (2.1) to (2.14) until t > t max ;

[0076] Step 2.16: Calculate the far-field wavelet sound pressure of the air gun, including virtual reflections from the sea surface: R s The distance between the air gun and the hydrophone is represented by the sea surface reflection coefficient, D1 is the distance between the air gun's reflection on the sea surface and the hydrophone, and D2 is the distance between the air gun's reflection on the sea surface and the hydrophone. It is the time delay of the air gun signal passing through D1 and D2.

[0077] In step S4, based on the t obtained from step S3... i Calculate Δt i Specifically, this involves calculating the time difference Δt between the time it takes for an air gun with a capacity of 70 cu.in, 100 cu.in, 150 cu.in, and 250 cu.in to reach the peak of the main pulse and the time it takes for an air gun with a capacity of 45 cu.in to reach the peak of the main pulse. i .

[0078] In step S5, the air gun array is specifically as follows: there are a total of 39 guns in the air gun array, of which 33 are working guns and 6 are empty guns, with a total capacity of 4040 cu.in.

[0079] In step S6, the wavelet of the air gun array described in step S5 is subjected to spectral analysis, which specifically includes: calculating the peak value of the main pulse, the virtual reflection value, and the peak value of the bubble pulse of the air gun array wavelet; performing spectral analysis on the wavelet through Fourier transform; using the maximum amplitude -6dB as the standard for judging the effective bandwidth; obtaining the effective bandwidth of the wavelet main pulse; and obtaining the main frequency of the wavelet main pulse.

[0080] Another object of the present invention is to provide a computer device comprising a memory and a processor, the memory storing a computer program, which, when executed by the processor, causes the processor to perform the method for broadening the wavelet band of an air gun source by three-dimensional arrangement and delayed excitation.

[0081] Another objective of this invention is to provide an air gun source for exploration of deep-sea geological targets, implementing the method described above for broadening the wavelet frequency band of the air gun source through three-dimensional arrangement and delayed excitation.

[0082] Another objective of this invention is to provide a marine oil and gas resource exploration device equipped with the air gun source used for exploring deep-sea geological targets, and to implement the method of widening the wavelet frequency band of the air gun source through three-dimensional arrangement and delayed excitation.

[0083] Combining all the above technical solutions, the advantages and positive effects of this invention are as follows:

[0084] First, in view of the technical problems existing in the prior art and the difficulty of solving these problems, and closely combining the technical solution to be protected by this invention with the results and data during the research and development process, this paper analyzes in detail how the technical solution of this invention solves the technical problems, and the inventive technical effects brought about after solving the problems, as described in detail below:

[0085] This invention constructs sharp pulse wavelets by setting the immersion depth of air guns with different capacities and adjusting the excitation time of air guns with different capacities, ultimately generating a source wavelet with high resolution and high penetration capability suitable for exploration of geological targets in shallow and deep seas.

[0086] This invention calculates the immersion depth of air guns with different capacities and the time it takes for the air gun to reach the peak value of the main pulse after excitation. Then, based on the calculated time, it adjusts the immersion depth and excitation time of air guns with different capacities to shift the time corresponding to the peak value of the main pulse of each air gun with different capacities in the air gun array. Finally, it constructs a sharp pulse source wavelet with a narrow main pulse waveform of the air gun array, thereby achieving the purpose of widening the source wavelet frequency band.

[0087] Secondly, considering the technical solution as a whole or from the perspective of the product, the technical effects and advantages of the technical solution to be protected by this invention are specifically described as follows:

[0088] This invention utilizes the relationship between the immersion depth of the air gun and virtual reflection, and the relationship between the air gun capacity and the peak arrival time of the main pulse. By adjusting the immersion depth and excitation time of air guns with different capacities, sharp pulse wavelets are constructed to suppress virtual reflection. This achieves the goal of extending the frequency band of the air gun array to low frequencies while ensuring high frequencies, ultimately obtaining an air gun source with rich high and low frequencies and strong energy transmission capability for targeting medium and deep geological targets. Attached Figure Description

[0089] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure;

[0090] Figure 1This is a flowchart of a method for broadening the wavelet frequency band of an air gun source by three-dimensional arrangement and delayed excitation, provided in an embodiment of the present invention.

[0091] Figure 2 These are simulated single-shot wavelet diagrams of air guns with different capacities provided in this embodiment of the invention.

[0092] Figure 3 This is a statistical chart showing the time from excitation to reaching the peak of the main pulse obtained from the simulation of a single air gun of each capacity in the air gun array provided in the embodiment of the present invention.

[0093] Figure 4 This is a plan view of the air gun array used in the embodiments of the present invention;

[0094] Figure 5(a) is a simulated broadband air gun wavelet diagram provided by an embodiment of the present invention;

[0095] Figure 5(b) is a simulated broadband air gun spectrum diagram provided by an embodiment of the present invention;

[0096] Figure 6(a) is a comparison diagram of the simulated broadband air gun wavelet provided by the embodiment of the present invention and the simulated wavelet of the conventional array;

[0097] Figure 6(b) is a comparison of the spectra of the simulated broadband air gun wavelet and the simulated wavelet of the conventional array provided by the embodiment of the present invention;

[0098] Figure 7 A velocity field model diagram of the Marmousi model provided in an embodiment of the present invention;

[0099] Figure 8(a) shows the actual air gun array used in a certain block of the Bohai Sea using a conventional array, with the array number 7-8_4040_7_66-air;

[0100] Figure 8(b) is a comparison of wave field imaging using the spike pulse wavelet constructed in this invention and wave field imaging using the Ricker wavelet. The array used in this invention is obtained by optimizing the array based on it, and the array is numbered Stereoscopic and delayed arrays. Detailed Implementation

[0101] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0102] I. Explanation of the Implementation Example:

[0103] Example 1

[0104] This invention provides a method for broadening the wavelet band of an air gun source by three-dimensional arrangement and delayed excitation, comprising:

[0105] By calculating the immersion depth of air guns with different capacities and the time it takes for the air gun to reach the peak value of the main pulse after excitation, and then adjusting the immersion depth and excitation time of air guns with different capacities based on the calculated time, the time shift corresponding to the peak value of the main pulse of each air gun with different capacities in the air gun array is achieved. Finally, a sharp pulse source wavelet with a narrow main pulse waveform of the air gun array is constructed to achieve the purpose of widening the source wavelet frequency band.

[0106] Specifically, such as Figure 1 As shown, an embodiment of the present invention provides a method for broadening the wavelet frequency band of an air gun source by three-dimensional arrangement and delayed excitation, comprising the following steps:

[0107] S101. Simulate gas gun wavelets of different capacities based on the van der Waals nonideal gas gas gun wavelet model, and set the initial conditions of the model.

[0108] S102. Execute the simulation process according to the initial conditions set in step S101;

[0109] S103. Analyze the simulated air gun wavelets and statistically analyze the time t from excitation to the peak value of the main pulse for air gun wavelets of different capacities. i ;

[0110] S104. According to the simulation results, the smaller the capacity t i The smaller the value, the less likely it is to be the minimum value t. i Let t0 be the time difference between Δt and t0 for different capacity air guns from excitation to reaching the peak of the main pulse. i , Δt i =t i -t0;

[0111] S105. Take half of the pressure difference calculated in step S104 as the delayed excitation time of air guns of different capacities in the air gun array, reduce the immersion depth of this part of the air guns, and then perform air gun wavelet simulation.

[0112] Wherein, 1 / 2 pressure difference is expressed as 1 / 2Δt i The immersion depth of this part of the air gun is reduced by 1 / 4Δt i •C, where C is the gas velocity.

[0113] S106. Perform spectral analysis on the air gun array wavelet obtained in step S105.

[0114] Example 2

[0115] Based on the method for broadening the wavelet frequency band of the air gun source through three-dimensional arrangement and delayed excitation provided in Embodiment 1 of the present invention, the equation of the van der Waals nonideal gas air gun wavelet model in step S101 is further expressed as:

[0116]

[0117] In the formula, a = 0.1404m 6 ·Pa·mol -2 b = 3.764 × 10 -5 m 3 ·mol -1 It is the van der Waals constant, T g For the effective thermodynamic temperature, R g m is the universal gas constant. g V is the mass of the gas. g For volume.

[0118] Laws et al. believe that the effective temperature T g Depends on the high-pressure gas in the chamber:

[0119] T g =T w (1+P g / P c (2)

[0120] In the formula P c =139MPa.

[0121] During the air gun firing process, high-pressure gas is ejected from the chamber, forming bubbles. Heat is transferred outwards through the bubble walls during this process, consistent with the characteristics of an open thermodynamic system. According to the law of conservation of energy, the energy gained from heat loss and mass transfer within the bubble must balance the change in internal energy. Therefore:

[0122]

[0123] In the formula, T is the bubble temperature, P is the bubble pressure, and m b It is the mass of the gas inside the bubble, U=C m m b T represents the internal energy of the bubble, C m and C m These are the isobaric specific heat capacity and the volumetric specific heat capacity, respectively. dQ / dt is the heat transfer rate through the bubble wall, and the heat transfer coefficient k is determined by fitting the model with experimental data. The bubble heat loss rate can be expressed as:

[0124]

[0125] In the formula, ΔT=T b-T w It is the bubble temperature T b and the surrounding water temperature T w The temperature difference between the two bubbles, where R is the bubble radius. The kinetic energy of gas molecules is affected by temperature, and the potential energy of gas molecules is affected by the change in volume. Therefore, using the van der Waals nonideal gas equation, the internal energy of a nonideal gas is a function of its temperature and volume:

[0126]

[0127] The total differential equation can be expressed as:

[0128]

[0129] Furthermore, the first law of thermodynamics can be transformed into:

[0130]

[0131] In the formula, R g =C m -C m .

[0132] To derive the rate of change of the amount of gaseous substance Introducing the throttling constant τ, which determines the rate at which the gas passes through the air gun port:

[0133] In the formula, V g It is the air chamber volume, m g It is the amount of gas in the chamber, P g It's the air gun pressure, P b It is bubble pressure.

[0134] For practical applications of air guns, the rate and total amount of high-pressure gas released into the water are controlled by parameters such as port size and port opening time, thus affecting the air gun's wavelet performance. Since the port area is fixed, the throttling constant τ improves the consistency between the model and measured data. It is assumed that the throttling constant for air guns of different capacities depends only on the chamber size. According to the power law, it can be expressed as:

[0135]

[0136] In the formula, τ0 is the port throttling constant independent of capacity, and ζ is the throttling power-law exponent determined by comparison with measured data. According to measurement and calculation results, the gas bubbles escaping into the water can persist for several milliseconds. At any given time, the gas flow rate through the air gun port depends on the pressure difference inside and outside the air gun, thus the gas release rate can be expressed as:

[0137]

[0138] In the formula, mb It is the amount of gaseous substance released into the bubble, m g | t＝0 η is the total amount of gas in the chamber, and η is the ratio of the amount of gas in the bubble to the total amount.

[0139] The equation of motion for the bubble wall can be expressed as:

[0140]

[0141] In the formula, R is the bubble radius, and u and These are the velocity and acceleration of the bubble wall, respectively, and c is the velocity of the sound wave in the fluid medium. It is the enthalpy difference of the bubble wall, ρ ∞ It is the still water density at infinity, P b It is the bubble pressure, P ∞ This is the hydrostatic pressure at infinity. The hydrostatic pressure of the bubble changes as it rises due to buoyancy, therefore the rise of the bubble must be considered. The expression for the vertical rising velocity of the bubble considering its rising process is:

[0142]

[0143] In the formula, z is the bubble depth, g is the gravitational acceleration constant, and R is the bubble radius. Therefore, the hydrostatic pressure P ∞ The expression is:

[0144]

[0145] In the formula, P atm It is standard atmospheric pressure, z g This refers to the air gun depth. At a distance of 1 meter from the air gun, the air gun wavelet signal can be expressed as:

[0146]

[0147] At low frequencies, the interaction between bubbles is not negligible. This interaction can be viewed as a regulation of the hydrostatic pressure of the fluid. The interaction between bubbles causes changes in the pressure around the bubbles. Relative to the seismic wavelength, a bubble can be considered a point; therefore, the pressure field around any arbitrary bubble is the superposition of the hydrostatic pressure and the time-varying pressure field generated by the bubble. Thus, the effective hydrostatic pressure at the i-th bubble is:

[0148]

[0149] In the formula, P ∞ It is hydrostatic pressure, ∑ k≠i ΔP ik It is the sum of the pressure contributions of all other air guns in the air gun array, ΔP ikIt consists of the hydrostatic pressure disturbance on the i-th bubble caused by the k-th bubble, and the time delay and pressure characteristics on the i-th bubble caused by the k-th bubble:

[0150]

[0151] In the formula, r ik This represents the distance between the i-th bubble and the k-th bubble.

[0152] Example 3

[0153] Based on the method for broadening the wavelet frequency band of the air gun source through three-dimensional arrangement and delayed excitation provided in Embodiment 2 of the present invention, the above-mentioned initial conditions are further as follows:

[0154] Step 1.1, Condition 1: Set the initial value P of the air gun pressure. g | t＝0 Set to working pressure;

[0155] Step 1.2, Condition 2: The initial temperature inside the bubble is set to T. g =T w (1+P g / P c );

[0156] Step 1.3, Condition 3: Initial volume V of the bubble b | t＝0 =V g The initial radius is

[0157] Step 1.4, Condition 4: The initial velocity of the bubble wall is u = 0;

[0158] Step 1.5, Condition 5: Initial pressure P of the bubble b | t＝0 =P ∞ The initial temperature is water temperature T. w =18°, the initial mass inside the bubble is

[0159] Step 1.6, Condition 6: Set the placement position (x, y, z) of each air gun.

[0160] Example 4

[0161] Based on the method for broadening the wavelet frequency band of an air gun source through three-dimensional arrangement and delayed excitation provided in Embodiment 1 of the present invention, further, in step S102, the simulation process performed according to the initial conditions set in step S101 is specifically as follows:

[0162] Step 2.1: Input the initial conditions for the van der Waals nonideal gas gun wavelet model;

[0163] Step 2.2: Start the time loop and calculate the bubble volume at time t = k.

[0164] Step 2.3: Calculate the bubble pressure P at time t = k using equation (1). b ;

[0165] Step 2.4: Calculate the bubble heat loss rate using equation (4).

[0166] Step 2.5: Calculate the gas release rate using equation (9).

[0167] Step 2.6: Calculate the rate of change of bubble volume at time t = k.

[0168] Step 2.7: Calculate the rate of temperature change inside the bubble at time t = k using equation (7).

[0169] Step 2.8: Calculate the enthalpy difference of the bubble wall.

[0170] Step 2.9: Obtain the rate of change of bubble pressure by differentiating equation (1) with respect to time t.

[0171] Step 2.10: Differentiate the enthalpy difference with respect to time t to obtain...

[0172] Step 2.11: Calculate the rate of change of the bubble wall velocity at time t = k using equation (10). The acceleration of the bubble wall;

[0173] Step 2.12, for Find the derivative with respect to time t to obtain...

[0174] Step 2.13: Since the air gun wavelet simulation is an iterative process, the bubble wall radius, bubble wall velocity, gas temperature, and mass of the gas inside the bubble can be obtained through second-order Taylor series expansion.

[0175] and

[0176] Step 2.14: Express the bubble pressure as a function of enthalpy, bubble wall velocity, and bubble radius: R0 is the distance from the bubble center to the far-field point;

[0177] Step 2.15: Repeat steps (2.1) to (2.14) until t > t max ;

[0178] Step 2.16: Calculate the far-field wavelet sound pressure of the air gun, including virtual reflections from the sea surface:

[0179] R s The distance between the air gun and the hydrophone is represented by the sea surface reflection coefficient, D1 is the distance between the air gun's reflection on the sea surface and the hydrophone, and D2 is the distance between the air gun's reflection on the sea surface and the hydrophone. It is the time delay of the air gun signal passing through D1 and D2.

[0180] Example 5

[0181] Based on the method for broadening the frequency band of the air gun source wavelet through three-dimensional arrangement and delayed excitation provided in Embodiment 1 of the present invention, further, in step S103, the air gun array wavelet simulated in step S102 is analyzed, and the time t from excitation to reaching the peak value of the main pulse for air guns of different capacities is statistically analyzed. i That is, the time ti when the main pulse peak is reached after the gas guns of different capacities of 45cu.in, 70cu.in, 100cu.in, 150cu.in, and 250cu.in are fired;

[0182] Among them, the time t for reaching the peak value of the main pulse after being fired by gas guns with capacities of 45 cu.in, 70 cu.in, 100 cu.in, 150 cu.in, and 250 cu.in is... i .

[0183] Example 6

[0184] Based on the method for broadening the wavelet frequency band of the air gun source through three-dimensional arrangement and delayed excitation provided in Embodiment 1 of the present invention, further, in step S104, according to the t obtained from step S103... i Calculate Δt i That is, calculate the time difference Δt between the time it takes for an air gun with a capacity of 70 cu.in, 100 cu.in, 150 cu.in, and 250 cu.in to reach the peak of the main pulse and the time it takes for an air gun with a capacity of 45 cu.in to reach the peak of the main pulse. i ;

[0185] Example 7

[0186] Based on the method for broadening the wavelet frequency band of the air gun source through three-dimensional arrangement and delayed excitation provided in Embodiment 1 of the present invention, the air gun array in step S105 is further defined as follows: the air gun array contains a total of 39 guns, of which 33 are working guns and 6 are empty guns, with a total capacity of 4040 cu.in. The single gun capacity and number of guns are 45 cu.in (6 guns), 70 cu.in (4 guns), 100 cu.in (10 guns, including 2 empty guns), 150 cu.in (11 guns, including 2 empty guns), and 250 cu.in (8 guns, including 2 empty guns), respectively. The calculation in step 4... The delayed firing times for different capacity air guns are as follows: 1.25 ms for 45 cu.in and 70 cu.in air guns, 1.0 ms for 100 cu.in and 150 cu.in air guns, and no delay for the 250 cu.in air gun. The immersion depth for the 45 cu.in and 70 cu.in air guns is 6.00 m, for the 100 cu.in and 150 cu.in air guns it is 6.25 m, and for the 250 cu.in air gun it is 7 m. The cable is immersed at a depth of 8 m.

[0187] Example 8

[0188] Based on the method for broadening the frequency band of the air gun source wavelet through three-dimensional arrangement and delayed excitation provided in Embodiment 1 of the present invention, further, in step S106, the wavelet of the air gun array described in step S105 is subjected to spectral analysis. Specifically, this includes: calculating the peak value of the main pulse, the virtual reflection value, and the peak value of the bubble pulse of the air gun array wavelet; performing spectral analysis on the wavelet through Fourier transform; and using the maximum amplitude of -6dB as the standard for judging the effective bandwidth. Therefore, the present invention uses -6dB to obtain the effective bandwidth of the main pulse of the wavelet and obtains the main frequency of the main pulse of the wavelet.

[0189] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0190] The information interaction and execution process between the above-mentioned devices / units are based on the same concept as the method embodiments of the present invention. For details on their specific functions and technical effects, please refer to the method embodiments section, and they will not be repeated here.

[0191] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this invention. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments.

[0192] II. Application Examples:

[0193] Application examples

[0194] The method for broadening the wavelet band of an air gun source by three-dimensional arrangement and delayed excitation provided in this embodiment of the invention includes the following steps:

[0195] Step 1: Simulate the air gun wavelet based on the van der Waals nonideal gas condition air gun wavelet model. First, set the initial conditions of the model. Specifically, this includes an air gun placement depth of 7m, a cable placement depth of 8m, and air gun capacities and numbers of 45cu.in, 70cu.in, 100cu.in, 150cu.in, and 250cu.in, respectively. The sampling interval is 0.0005s, and the seawater density is 1.03g / cm³. 3 The seawater velocity is 1500 m / s, the seawater temperature is 293.15 Kelvin, and the sea surface reflectance is -0.9.

[0196] Step 2: Perform the simulation process based on the initial conditions set in Step 1. The specific execution process is as follows:

[0197] a) Input all the initial conditions for the air gun wavelet model.

[0198] b) Start the time loop and calculate the bubble volume at time t = k.

[0199] c) Calculate the bubble pressure P at time t = k using equation (1). b ;

[0200] d) Calculate the bubble heat loss rate using equation (4).

[0201] e) Calculate the gas release rate using equation (9).

[0202] f) Calculate the rate of change of bubble volume at time t = k.

[0203] g) Calculate the rate of temperature change inside the bubble at time t = k using equation (7).

[0204] h) Calculate the enthalpy difference of the bubble wall.

[0205] i) The rate of change of bubble pressure is obtained by differentiating equation (1) with respect to time t.

[0206] j) Taking the derivative of the enthalpy difference with respect to time t, we get...

[0207] k) Calculate the rate of change of the bubble wall velocity at time t = k using equation (10). The acceleration of the bubble wall;

[0208] l) To Find the derivative with respect to time t to obtain...

[0209] m) Since the air gun wavelet simulation is an iterative process, the bubble wall radius, bubble wall velocity, gas temperature, and mass of the gas inside the bubble can be obtained through second-order Taylor series expansion: and

[0210] n) Express the bubble pressure as a function of enthalpy, bubble wall velocity, and bubble radius: R0 is the distance from the bubble center to the far-field point;

[0211] o) Repeat steps (a) to (n) until t > t max ;

[0212] p) Calculate the far-field wavelet sound pressure of the air gun, including virtual reflections from the sea surface:

[0213] q) R s The distance between the air gun and the hydrophone is represented by the sea surface reflection coefficient, D1 is the distance between the air gun's reflection on the sea surface and the hydrophone, and D2 is the distance between the air gun's reflection on the sea surface and the hydrophone. This represents the time delay of the airgun signal after passing through D1 and D2. After steps (a) to (q), airgun sub-waves of different capacities are obtained, and statistical results are obtained as follows: Figure 1 The different capacities of the air gun sub-waves are shown.

[0214] Step 3: Calculate the time t taken for the wavelet of different capacity air guns to reach the peak value of the main pulse from excitation. i ,like Figure 2 As shown.

[0215] Step 4: Calculate t based on the results obtained in Step 3. i Calculate Δt i ;

[0216] Step 5: Based on the set initial conditions, simulate the spike pulse wavelet air gun array. The specific process is as follows: The air gun array contains 39 guns, of which 33 are operational and 6 are unloaded. The total capacity is 4040 cu.in. The capacities and numbers of individual guns are 45 cu.in (6 guns), 70 cu.in (4 guns), 100 cu.in (10 guns, including 2 unloaded guns), 150 cu.in (11 guns, including 2 unloaded guns), and 250 cu.in (8 guns, including 2 unloaded guns). The 1 / 2Δt calculated in Step 4 is used as the delayed excitation time for different capacities of air guns: 1.25 ms for 45 cu.in and 70 cu.in air guns, 1.0 ms for 100 cu.in and 150 cu.in air guns, and no delay for the 250 cu.in air gun. The sinking depth for 45cu.in / 70cu.in air guns is 6.00m, for 100cu.in / 150cu.in air guns it is 6.25m, and for 250cu.in air guns it is 7m. The sinking depth for the cable is 8m. Figure 3 The image shown is a plan view of the air gun array.

[0217] Step 6: Perform spectral analysis on the sharp pulse wavelet based on Fourier transform, and obtain the following results: Figure 4 The spike pulse wavelet and its spectrum are shown. To better demonstrate the technical advantages of this invention, a comparison was made with the wavelet of an actual airgun array in a certain block of the Bohai Sea, as shown in Figure 5(a). The wavelet comparison in Figure 5(b) shows that, after adopting the method of this invention, the bandwidth of the obtained airgun wavelet is broadened, and the low-frequency energy in the spectrum is enhanced, as shown in Figure 5(b).

[0218] Application examples

[0219] This invention also provides a method for high-precision full-waveform wavefield imaging using obtained sharp pulse wavelets. The specific method for this full-waveform wavefield imaging includes velocity field data from actual exploration in a block of the Bohai Sea, the sharp pulse wavelet constructed in this invention, and a calculation method for wavefield imaging.

[0220] The velocity field data of the Marmousi model are as follows: Figure 7As shown, the model basically includes various geological structures such as cracks, faults, depressions, synclines, anticlines, and buried hills. Imaging the model can comprehensively reflect the quality of seismic wavelets.

[0221] The spike pulse wavelet is constructed using the present invention, and the wave field imaging calculation method is a currently conventional calculation method.

[0222] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail or in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0223] III. Evidence of the relevant effects of the embodiments:

[0224] Figures 8(a) and 8(b) show a comparison of the wave field imaging effects of the spike pulse wavelet constructed by the present invention and the conventional wavelet. The wave field imaging effect completed by the spike pulse wavelet constructed by the present invention is better, specifically with stronger energy, deeper downlink depth, wider width, and clearer characterization of the structure of medium and deep buried hills and inner areas.

[0225] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention and within the spirit and principles of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for broadening the wavelet frequency band of an air gun source by three-dimensional arrangement and delayed excitation, characterized in that, This method calculates the placement depth of air guns with different capacities and the time it takes for the air guns to reach the peak value of the main pulse after excitation. Then, based on the calculated time, it adjusts the placement depth of air guns with different capacities and simultaneously adjusts the excitation time of these air guns, causing a time shift corresponding to the peak value of the main pulse for each air gun with different capacities in the air gun array. Finally, it constructs a narrow-bandwidth spike pulse source wavelet for the air gun array's main pulse waveform, thus achieving a widening of the source wavelet's frequency band. Specifically, it includes the following steps: S1. Simulate gas gun wavelets of different capacities based on the van der Waals nonideal gas gas gun wavelet model and set initial conditions. S2. Execute the simulation process according to the initial conditions set in step S1; S3. Analyze the simulated air gun wavelets and statistically analyze the time t from excitation to the peak value of the main pulse for air gun wavelets of different capacities. i ; S4. According to the simulation results, the smaller the capacity t i The smaller the value, the less likely it is to be the minimum value t. i Let t0 be the time difference between the time from excitation to the peak value of the main pulse and t0 for air guns of different capacities. , ; S5. Take half of the result calculated in step S4. As a delay firing time for air guns of different capacities in the air gun array, the immersion depth of this part of the air guns is reduced by 1 / 4. C represents the gas velocity, followed by a gas gun wavelet simulation. S6. Perform spectral analysis on the air gun array wavelet obtained in step S5.

2. The method for broadening the wavelet frequency band of an air gun source by three-dimensional arrangement and delayed excitation according to claim 1, characterized in that, In step S1, the equations of the van der Waals nonideal gas gun wavelet model are expressed as follows: （1） In the formula, a and b are both van der Waals constants. T g For the effective thermodynamic temperature, R g m is the universal gas constant. g V is the mass of the gas. g For volume; Effective temperature T g Depends on the high-pressure gas in the chamber: （2） In the formula, ; During the air gun firing process, according to the law of conservation of energy, the energy gained from heat transfer and mass transfer of the bubble must be balanced with the change in the bubble's internal energy. Therefore: （3） In the formula, It is the temperature of the bubble. It is bubble pressure. It is the mass of the gas inside the bubble. This represents the internal energy of the bubble. It is the specific heat capacity at constant pressure. It refers to the heat transfer rate through the bubble wall, and the heat transfer coefficient. The bubble heat loss rate was determined by fitting the model to experimental data and is expressed as: （4） In the formula, It is the temperature of the bubble. and the surrounding water temperature The temperature difference between them It is the bubble radius; using the van der Waals' nonideal gas equation, the internal energy of a nonideal gas is a function of the gas temperature and volume: （5） The total differential equation is expressed as: （6） The first law of thermodynamics is transformed into: （7） In the formula, ; rate of change of the amount of gaseous substance Throttling constant , It is the air chamber capacity. It is the amount of matter in the gas inside the chamber. It's the air gun pressure. It is bubble pressure; The throttling constant of air guns with different capacities depends only on the size of the air chamber; according to the power law, it can be expressed as: （8） In the formula, It is a port throttling constant that is independent of capacity. The throttling power law exponent is determined by comparing with measured data; based on the measurement and calculation results, the gas flow rate through the air gun port at any given time depends on the pressure difference inside and outside the air gun, and the gas release rate is expressed as: （9） In the formula, It is the amount of gaseous substance released into the bubbles. It is the total amount of gas in the chamber. It is the ratio of the amount of gas in the bubble to the total amount of gas. The equation of motion for the bubble wall is expressed as: （10） In the formula, It is the bubble radius. and These are the velocity and acceleration of the bubble wall, respectively. It is the speed of sound waves in a fluid medium. It is the enthalpy difference of the bubble wall. It is the still water density at infinity. It is bubble pressure. It is the hydrostatic pressure at infinity; the hydrostatic pressure of the bubble changes as the bubble rises due to buoyancy, and the expression for the vertical rising velocity of the bubble during the rising process is: （11） In the formula, Where is the bubble depth, and g is the gravitational acceleration constant. It is the bubble radius and hydrostatic pressure. The expression is: （12） In the formula, It is standard atmospheric pressure. It's the depth of the air gun; At a distance of 1m from the air gun, the air gun wavelet signal is represented as: （13） At low frequencies, the interaction between bubbles cannot be ignored; this interaction between bubbles regulates the hydrostatic pressure of the fluid; the interaction between bubbles causes changes in the pressure around the bubbles. Relative to the seismic wavelength, a bubble is a point, and the pressure field around any bubble is the superposition of the hydrostatic pressure and the time-varying pressure field generated by the bubble; the effective hydrostatic pressure at the j-th bubble is; （14） In the formula, It is hydrostatic pressure. It is the sum of the pressure contributions of all other air guns in the air gun array. It is the first The hydrostatic pressure disturbance on the j-th bubble caused by the first bubble, and the... The time delay and pressure characteristics on the distance scale caused by each bubble: （15） In the formula, This indicates that the j-th bubble is related to the j-th bubble. The spacing between bubbles.

3. The method for broadening the wavelet frequency band of an air gun source by three-dimensional arrangement and delayed excitation according to claim 1, characterized in that, In step S1, the initial conditions specifically include: Step 1.1, Condition 1: Set the initial value of the air gun pressure. Set to working pressure; Step 1.2, Condition 2: The initial temperature inside the bubble is set to... ; Step 1.3, Condition 3: Initial volume of the bubble The initial radius is ; Step 1.4, Condition 4: The initial velocity of the bubble wall is ; Step 1.5, Condition 5: Initial pressure of the bubble The initial temperature is the water temperature. The initial mass of the substance inside the bubble is ; Step 1.6, Condition 6: Set the placement position (x, y, z) of each air gun.

4. The method for broadening the frequency band of the air gun source wavelet through three-dimensional arrangement and delayed excitation according to claim 1, characterized in that, In step S2, the simulation process is executed according to the initial conditions set in step S1, specifically as follows: Step 2.1: Input the initial conditions for the van der Waals nonideal gas gun wavelet model; Step 2.2: Start the time loop and calculate the bubble volume at time t=k. ; Step 2.3: Calculate the bubble pressure at time t=k using equation (1). ; Step 2.4: Calculate the bubble heat loss rate using equation (4). ; Step 2.5: Calculate the gas release rate using equation (9). ; Step 2.6, Calculation The rate of change of bubble volume at time t. ; Step 2.7: Calculate using equation (7) The rate of temperature change inside the bubble at any given time. ; Step 2.8: Calculate the enthalpy difference of the bubble wall. ; Step 2.9: Solve equation (1) for time. The rate of change of bubble pressure is obtained by the derivative. ; Step 2.10: Calculate the enthalpy difference with respect to time. The derivative is obtained, ; Step 2.11: Calculate using equation (10) The rate of change of the velocity of the bubble wall at time t. , which is the acceleration of the bubble wall; Step 2.12, for , , , , , Seeking information about time The derivative is obtained, , , , , , ; Step 2.13: Since the air gun wavelet simulation is an iterative process, the bubble wall radius, bubble wall velocity, gas temperature, and mass of the gas inside the bubble can be obtained through second-order Taylor series expansion. , , , and ; Step 2.14: Express the bubble pressure as a function of enthalpy, bubble wall velocity, and bubble radius: , This is the distance from the bubble center to the far-field point; Step 2.15: Repeat steps (2.1) to (2.14) until... ; Step 2.16: Calculate the far-field wavelet sound pressure of the air gun, including virtual reflections from the sea surface: , Indicates the sea surface reflectance. The distance between the air gun and the hydrophone is... It is the distance between the image of the air gun on the sea surface and the hydrophone. It is the air gun signal passing through and The time delay.

5. The method for broadening the wavelet frequency band of an air gun source by three-dimensional arrangement and delayed excitation according to claim 1, characterized in that, In step S4, based on the t obtained from step S3... i Calculate Δt i Specifically, this involves calculating the time difference between the time it takes for an air gun with a capacity of 70 cu.in, 100 cu.in, 150 cu.in, and 250 cu.in to reach the peak of the main pulse and the time it takes for an air gun with a capacity of 45 cu.in to reach the peak of the main pulse. .

6. The method for broadening the wavelet frequency band of an air gun source by three-dimensional arrangement and delayed excitation according to claim 1, characterized in that, In step S5, the air gun array is specifically as follows: there are a total of 39 guns in the air gun array, of which 33 are working guns and 6 are empty guns, with a total capacity of 4040 cu.in.

7. The method for broadening the wavelet frequency band of an air gun source by three-dimensional arrangement and delayed excitation according to claim 1, characterized in that, In step S6, the wavelet of the air gun array described in step S5 is subjected to spectral analysis, which specifically includes: calculating the peak value of the main pulse, the virtual reflection value, and the peak value of the bubble pulse of the air gun array wavelet; performing spectral analysis on the wavelet through Fourier transform; using the maximum amplitude -6dB as the standard for judging the effective bandwidth; obtaining the effective bandwidth of the wavelet main pulse; and obtaining the main frequency of the wavelet main pulse.

8. A computer device, characterized in that, The computer device includes a memory and a processor. The memory stores a computer program, which, when executed by the processor, causes the processor to perform the method for broadening the wavelet band of an air gun source by three-dimensional arrangement and delayed excitation as described in any one of claims 1-7.

9. An air gun source for exploration of deep geological targets in the ocean, comprising the method described in any one of claims 1-7 for widening the wavelet frequency band of the air gun source through three-dimensional arrangement and delayed excitation.

10. A marine oil and gas resource exploration device equipped with the air gun source of claim 9 for exploration of deep-sea geological targets, implementing the method of widening the wavelet frequency band of the air gun source by three-dimensional arrangement and delayed excitation as described in any one of claims 1-7.

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