Method for broadening airgun source frequency band by using delayed excitation configuration wide pulse sub-wave and application thereof

Abstract

This invention belongs to the field of airgun source data identification technology in marine seismic exploration, and discloses a method and application for widening the frequency band of airgun sources by constructing a wide pulse wavelet using delayed excitation. First, the time to reach the peak of the main pulse after excitation of the airgun with different capacities is calculated. Then, based on the obtained time, the excitation time of the airguns with different capacities is adjusted so that the time for each airgun in the array to reach the peak of the main pulse is delayed accordingly. This constructs a wide pulse wavelet with a relatively wide main pulse waveform and an approximate trapezoidal shape, achieving the goal of extending the low-frequency range while ensuring the high frequency of the source. This invention utilizes the relationship between airgun capacity and the time to reach the peak of the main pulse. By regularly adjusting the delayed excitation time of airguns with different capacities, a wide pulse wavelet is constructed. Comparison shows that the goal of extending to low frequencies while ensuring high frequencies is achieved, ultimately obtaining an airgun source with rich high and low frequency frequencies and strong energy transmission capability for targeting medium-deep geological targets.

Description

Technical Field

[0001] This invention belongs to the field of air gun source data identification technology in marine seismic exploration, and particularly relates to the method and application of delay-excitation constructing wide pulse wavelet to broaden the air gun source frequency band. 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 for exploration of mid-to-deep ocean targets, where low-frequency energy in the source is paramount. With the large-scale exploitation of mid-to-deep ocean oil and gas resources, airgun seismic sources rich in low-frequency energy are receiving increasing attention. High-capacity airguns can contribute more low-frequency signals, but the corresponding bubble oscillations are stronger.

[0003] Currently, both domestically and internationally, the main approach is to utilize multi-subarray planar and three-dimensional combinations, employing tuned wavelet energy, to broaden the source wavelet frequency band and improve the downlink capability of seismic exploration. While multi-subarray combinations significantly enhance the high-frequency range of the source, the effect on extending the source frequency band to lower frequencies is less pronounced. How to ensure both high-frequency and low-frequency extension remains a pressing issue in geophysics. Suppressing sea surface virtual reflections and improving the low-frequency energy of the source, as well as the downlink capability of seismic waves, are challenges that current technologies cannot solve.

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

[0005] (1) Existing technologies have weak down-transmission capability of air gun seismic sources targeting medium-deep geological targets;

[0006] (2) The existing technology for air gun seismic sources has low resolution for medium and deep exploration and unclear structural characterization.

[0007] (3) Existing technologies cannot control the excitation time of air guns of different capacities to extend the low frequency of the source and broaden the frequency of the source wavelet, so the generated seismic wavelet with underground transmission capacity cannot meet the relevant quality requirements for exploration of shallow and deep geological targets. Summary of the Invention

[0008] To overcome the problems existing in related technologies, the present invention discloses a method and application for widening the frequency band of air gun seismic sources by constructing wide pulse wavelets through delayed excitation, which is used in a broadband three-dimensional marine field observation system to explore and collect seismic reflection signals in shallow and deep waters near the coast and to be used for marine geological surveys and oil and gas exploration.

[0009] The technical solution is as follows: A method for broadening the frequency band of an air gun source by constructing a wide pulse wavelet through delayed excitation, comprising the following steps:

[0010] S1. 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.

[0011] S2. Execute the simulation process according to the initial conditions of the set model;

[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. Based on the simulation results, calculate the difference Δt between the time from excitation to reaching the peak of the main pulse and the minimum time t0 for air guns of different capacities. i ;

[0014] S5. Calculate the Δt i As the delayed excitation time of air guns of different capacities in the air gun array, the air gun wavelet simulation is then performed to generate the air gun array wavelet with a wide pulse shape.

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

[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 van der Waals constants: 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. g V is the mass of the gas. g For volume, P g This refers to the air gun pressure.

[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, T w Water temperature;

[0022] According to the law of conservation of energy, the energy gained from heat transfer and mass transfer within the bubble is 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 v m b T represents the internal energy of the bubble, C m and C v Here, dQ / dt represents the specific heat capacity at constant pressure and the specific heat capacity at constant volume, respectively. dQ / dt is the heat transfer rate through the bubble wall, dt is the unit time interval of bubble wall movement, dQ is the heat transferred from the bubble to the surrounding environment per unit time interval, dU is the decrease in internal energy of the bubble per unit time, dV is the change in bubble volume per unit time, and dm is the change in mass of the substance inside the bubble per unit time. The heat transfer coefficient k is determined by fitting the model with experimental data. 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;

[0027] Using the van der Waals nonideal gas equation, the internal energy of a nonideal gas is a function of its temperature and volume:

[0028]

[0029] The total differential equation is expressed as:

[0030]

[0031] Furthermore, the first law of thermodynamics can be transformed into:

[0032]

[0033] In the formula, R g =C p -C v C p The molar heat capacity under constant pressure, The rate of change of the amount of gaseous substance;

[0034] The throttling constant of air guns with different capacities is related to the size of the air chamber, and according to the power law, it can be expressed as:

[0035]

[0036] 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; at any given time, the gas flow rate through the air gun port depends on the pressure difference inside and outside the air gun, and the gas release rate is expressed as:

[0037]

[0038] 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, η is the ratio of the amount of gas in the bubble to the total amount, throttling constant τ, V g air chamber volume, m g The amount of gas in the chamber, P g It's the air gun pressure, P b It is bubble pressure;

[0039] The equation of motion for the bubble wall is expressed as:

[0040]

[0041] 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 expression for the vertical rising velocity of the bubble during the bubble's ascent is:

[0042]

[0043] 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:

[0044]

[0045] In the formula, P atm It is standard atmospheric pressure, z g This refers to the air gun depth; at a distance of 1m from the air gun, the air gun wavelet signal is represented as:

[0046]

[0047] 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 of the model are set as follows:

[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 performed according to the set initial conditions of the model, 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 are obtained through second-order Taylor series expansion.

[0073]

[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:

[0077] 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.

[0078] In step S3, the time t from excitation to the peak value of the main pulse for gas gun wavelets of different capacities is statistically analyzed. i This includes: statistically analyzing the time t it takes for the main pulse to reach its peak value after being fired from gas guns with capacities of 45 cu.in, 70 cu.in, 100 cu.in, 150 cu.in, and 250 cu.in. i .

[0079] In step S4, the difference Δt between the time from excitation to reaching the peak of the main pulse and the minimum time t0 is calculated for air guns of different capacities. i To calculate the time difference Δt between the time it takes for a gas 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 a gas gun with a capacity of 45 cu.in to reach the peak of the main pulse. i .

[0080] In step S5, the generation of the wide pulse pattern of the air gun array sub-wavelet is 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. The single gun capacity and number of guns are 45 cu.in, 70 cu.in, 100 cu.in, 150 cu.in and 250 cu.in, respectively.

[0081] In step S6, the spectral analysis of the obtained air gun array wavelet 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 of -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.

[0082] Another objective of this invention is to provide a high-capacity air gun that implements the method of widening the air gun source frequency band by constructing a wide pulse wavelet through delayed excitation.

[0083] Another objective of this invention is to provide an application of the method described above for widening the air gun source bandwidth by constructing a wide pulse wavelet through delayed excitation in a broadband three-dimensional marine field observation system, as well as in marine geological survey and oil and gas exploration equipment.

[0084] Combining all the above technical solutions, the advantages and positive effects of this invention are as follows:

[0085] First, addressing the technical problems and difficulties in solving the existing technologies, and closely combining the technical solution to be protected by this invention with the results and data from the research and development process, this invention provides a detailed and in-depth analysis of how the technical solution solves the technical problems and the creative technical effects it brings after solving the problems. The specific description is as follows: This invention first calculates the time it takes for the excitation of air guns with capacities of 45.in, 70cu.in, 45.in, 100cu.in, 150cu.in, and 250cu.in to reach the peak of the main pulse. Then, based on the obtained time, the excitation time of the air guns with different capacities is adjusted, so that the time for each air gun in the array to reach the peak of the main pulse has a corresponding time delay. This constructs a wide pulse wavelet with a relatively wide main pulse waveform and an approximate trapezoidal shape, achieving the goal of ensuring high frequency of the seismic source while extending low frequency. This invention utilizes the relationship between air gun capacity and the time to reach the peak of the main pulse, as shown in the attached diagram. Figure 2 As shown in the attached figure, by regularly adjusting the delayed firing time of air guns with different capacities, the following configuration is constructed. Figure 4 The wide pulse wavelet shown, as can be seen from the comparison in Figure 5, achieves the goal of extending to low frequencies while ensuring high frequencies, and ultimately obtains an air gun source with rich high and low frequencies and strong energy transmission capability for medium and deep geological targets.

[0086] Secondly, considering the technical solution as a whole or from a product perspective, the technical effects and advantages of the technical solution protected by this invention are specifically described as follows: This invention achieves the purpose of extending the low frequency of the seismic source and broadening the frequency band of the seismic source wavelet by controlling the excitation time of air guns of different capacities, thereby generating a high-resolution seismic wavelet with strong downlink capability to meet the relevant quality requirements for exploration of shallow and medium-deep geological targets. The wide-pulse wavelet provided by this invention has a richer frequency composition and better high- and low-frequency compatibility. Attached Figure Description

[0087] 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;

[0088] Figure 1 This is a flowchart of a method for widening the frequency band of an air gun source by constructing a wide pulse wavelet through delayed excitation, provided in an embodiment of the present invention.

[0089] Figure 2 These are simulated single-shot sub-waves of air guns with different capacities provided in the embodiments of the present invention;

[0090] 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.

[0091] Figure 4 This is a plan view of the air gun array used in the embodiments of the present invention;

[0092] Figure 5 is a simulated wide-pulse air gun sub-wave and spectrum diagram provided by an embodiment of the present invention;

[0093] Figure 5(a) is a simulated wide pulse wavelet diagram provided by an embodiment of the present invention;

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

[0095] Figure 6(a) is a wavelet diagram of the simulated time-pressure pulse relationship provided by an embodiment of the present invention;

[0096] Figure 6(b) is a wavelet diagram of the frequency-power relationship simulated by a conventional array provided in the embodiment of the present invention;

[0097] Figure 7 It is the velocity field model of the Marmousi model provided in the embodiments of the present invention;

[0098] Figure 8(a) is a conventional air gun wavelet wave field imaging (71_4040_7_66-air) provided by an embodiment of the present invention;

[0099] Figure 8(b) is a wide-pulse wavelet wave field imaging (71_4040_7_66-air-broad pulse-3) constructed using the present invention, provided by an embodiment of the present invention. Detailed Implementation

[0100] 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.

[0101] I. Explanation of the Implementation Example:

[0102] The method for widening the source bandwidth of an air gun by constructing a wide pulse wavelet through delayed excitation provided in this embodiment of the invention first calculates the time to the peak value of the main pulse after excitation of an air gun with a capacity of 45.in\70cu.in\45.in\100cu.in\150cu.in\250cu.in.

[0103] Then, based on the time obtained above, the excitation time of the air guns with different capacities is adjusted so that the time for each air gun in the array to reach the peak value of the main pulse is delayed accordingly, thereby constructing a wide pulse wavelet with a wide main pulse waveform and an approximate trapezoidal shape, so as to achieve the purpose of extending the low frequency while ensuring the high frequency of the source.

[0104] Example 1

[0105] like Figure 1 As shown, the method for widening the frequency band of an air gun source by constructing a wide pulse wavelet through delayed excitation provided in this embodiment of the invention includes the following steps:

[0106] 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.

[0107] S102. Execute the simulation process according to the initial conditions set in step S101;

[0108] 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 ;

[0109] 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 ;

[0110] S105, calculate Δt in step S104. i As the delayed excitation time of air guns of different capacities in the air gun array, air gun wavelet simulation is then performed to generate air gun wavelets with a wide pulse shape.

[0111] For example, the shape of the main pulse of a conventional air gun wavelet is a "right triangle" with a large apex angle, while the shape of the main pulse of a wide pulse wavelet is similar to an isosceles trapezoid, and the duration of the main pulse is increased by about 2ms.

[0112] S106. Perform spectral analysis on the air gun array wavelet obtained in step S105.

[0113] Example 2

[0114] Based on the method for broadening the frequency band of the air gun source by constructing a wide pulse wavelet through delayed excitation provided in Example 1, more preferably, the equation of the van der Waals nonideal gas air gun wavelet model in step S101 is expressed as:

[0115]

[0116] In the formula, a = 0.1404m6 ·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; Pg This refers to the air gun pressure.

[0117] Laws et al. believe that the effective temperature T g Depends on the high-pressure gas in the chamber:

[0118] T g =T w (1+P g / P c (2)

[0119] In the formula, P c =139MPa. T w This refers to the water temperature.

[0120] 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:

[0121]

[0122] 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 v m b T represents the internal energy of the bubble, C m and C v Here, dQ / dt represents the specific heat capacity at constant pressure and the specific heat capacity at constant volume, respectively. dQ / dt is the heat transfer rate through the bubble wall, dt is the unit time interval of bubble wall movement, dQ is the heat transferred from the bubble to the surrounding environment per unit time interval, dU is the decrease in internal energy of the bubble per unit time, dV is the change in bubble volume per unit time, and dm is the change in mass of the substance inside the bubble per unit time. The heat transfer coefficient k is determined by fitting the model with experimental data. The bubble heat loss rate is expressed as:

[0123]

[0124] In the formula, ΔT=T b -T w It is the bubble temperature T b and the surrounding water temperature Tw The temperature difference between them, where R is the bubble radius.

[0125] The kinetic energy of gas molecules is affected by temperature, while their potential energy is affected by changes 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 is expressed as:

[0128]

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

[0130]

[0131] In the formula, R g =C p -C v C p The molar heat capacity under constant pressure, Let be the rate of change of the amount of gaseous substance; introduce the throttling constant τ, which determines the rate at which the gas passes through the air gun port:

[0132] 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:

[0133]

[0134] 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:

[0135]

[0136] In the formula m b It is the amount of gaseous substance released into the bubble, m g | t＝0 V 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. In the formula... g air chamber volume, m g The amount of gas in the chamber, P gIt's the air gun pressure, P b It is bubble pressure.

[0137] The equation of motion for the bubble wall can be expressed as:

[0138]

[0139] 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. ρ∞ is the enthalpy difference of the bubble walls, ρ∞ is the still water density at infinity, and P is the density of water at infinity. 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:

[0140]

[0141] 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:

[0142]

[0143] 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:

[0144]

[0145] 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:

[0146]

[0147] 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:

[0148]

[0149] In the formula r ik This represents the distance between the i-th bubble and the k-th bubble.

[0150] Example 3

[0151] Based on the method for broadening the frequency band of a gas gun source by constructing a wide pulse wavelet through delayed excitation provided in Example 1, more preferably, in step S101, a van der Waals nonideal gas gas gun wavelet model is adopted, and the above initial conditions are specifically as follows:

[0152] Step 1.1, Condition 1: Set the initial value P of the air gun pressure. g | t＝0 Set to working pressure;

[0153] Step 1.2, Condition 2: The initial temperature inside the bubble is set to T. g =T w (1+P g / P c );

[0154] Step 1.3, Condition 3: Initial volume V of the bubble b | t＝0 =V g The initial radius is

[0155] Step 1.4, Condition 4: The initial velocity of the bubble wall is u = 0;

[0156] 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

[0157] Step 1.6, Condition 6: Set the placement position (x, y, z) of each air gun.

[0158] Example 4

[0159] Based on the method for broadening the air gun source frequency band by constructing a wide pulse wavelet through delayed excitation provided in Example 1, and more preferably, step S102 is performed during the simulation based on the set initial conditions.

[0160] The van der Waals nonideal gas gun wavelet model used in this invention is an improvement on the ideal gas gun wavelet model. The simulation execution process (the simulation process performed according to the initial conditions set in step S101) is as follows:

[0161] Step 2.1: Input the initial conditions for the van der Waals nonideal gas gun wavelet model;

[0162] Step 2.2: Start the time loop and calculate the bubble volume at time t = k.

[0163] Step 2.3: Calculate the bubble pressure P at time t = k using equation (1). b ;

[0164] Step 2.4: Calculate the bubble heat loss rate using equation (4).

[0165] Step 2.5: Calculate the gas release rate using equation (9).

[0166] Step 2.6: Calculate the rate of change of bubble volume at time t = k.

[0167] Step 2.7: Calculate the rate of temperature change inside the bubble at time t = k using equation (7).

[0168] Step 2.8: Calculate the enthalpy difference of the bubble wall.

[0169] Step 2.9: Obtain the rate of change of bubble pressure by differentiating equation (1) with respect to time t.

[0170] Step 2.10: Differentiate the enthalpy difference with respect to time t to obtain...

[0171] 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;

[0172] Step 2.12, for Find the derivative with respect to time t to obtain...

[0173] 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.

[0174]

[0175] 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;

[0176] Step 2.15: Repeat steps (2.1) to (2.14) until t > t max ;

[0177] Step 2.16: Calculate the far-field wavelet sound pressure of the air gun, including virtual reflections from the sea surface:

[0178] 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.

[0179] Example 5

[0180] Based on the method for broadening the frequency band of an air gun source by constructing a wide pulse wavelet through delayed excitation provided in Example 1, and further preferably, 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 is statistically analyzed for air guns of different capacities. 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.

[0181] Example 6

[0182] Based on the method for broadening the frequency band of an air gun source by constructing a wide pulse wavelet through delayed excitation provided in Example 1, and further preferably, in step S104, Δt is calculated based on the statistically obtained ti from step S103. i That is, to calculate the time difference Δti between the time it takes for an air gun with a capacity of 70cu.in, 100cu.in, 150cu.in, and 250cu.in to reach the peak of the main pulse and the time it takes for an air gun with a capacity of 45cu.in to reach the peak of the main pulse.

[0183] Example 7

[0184] Based on the method for widening the air gun source frequency band by constructing a wide pulse wavelet through delayed excitation provided in Example 1, more preferably, in step S105, a wide pulse wavelet air gun array simulation is performed according to the set initial conditions. The air gun array specifically consists of 39 guns, of which 33 are working guns and 6 are unloaded guns. The total capacity is 4040 cu.in, and 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 unloaded guns), 150 cu.in (11 guns, including 2 unloaded guns), and 250 cu.in (8 guns, including 2 unloaded guns), respectively.

[0185] The Δt calculated in step S104i The delayed excitation times for air guns of different capacities are as follows: no delay for 45 cu.in and 70 cu.in air guns; 1.0 ms delayed excitation for 100 cu.in and 150 cu.in air guns; and 2.0 ms delayed excitation for 250 cu.in air guns. The array is submerged at a depth of 6 m, and the cable is submerged at a depth of 8 m.

[0186] In one embodiment of the present invention, step S106 performs spectral analysis on the wavelet of the air gun array described in step S105. Specifically, this includes:

[0187] 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 are calculated. The wavelet is subjected to spectrum analysis by Fourier transform. The maximum amplitude of -6dB is used as the standard for judging the effective bandwidth. Therefore, this invention uses -6dB to obtain the effective bandwidth of the wavelet main pulse and obtains the main frequency of the wavelet main pulse.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] II. Application Examples:

[0192] Application Example 1

[0193] The method for widening the air gun source bandwidth by constructing a wide pulse wavelet through delayed excitation provided in this embodiment of the invention includes:

[0194] 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, these include 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, the seawater density is 1.03g / cm3, the seawater velocity is 1500m / s, the seawater temperature is 293.15 Kelvin, and the sea surface reflectance is -0.9, etc.

[0195] Step 2: Perform the simulation process based on the initial conditions set in Step 1. The specific execution process is as follows:

[0196] a) Input all the initial conditions for the air gun wavelet model.

[0197] b) Start the time loop and calculate the bubble volume at time t = k.

[0198] c) Calculate the bubble pressure P at time t = k using equation (1). b ;

[0199] d) Calculate the bubble heat loss rate using equation (4).

[0200] e) Calculate the gas release rate using equation (9).

[0201] f) Calculate the rate of change of bubble volume at time t = k.

[0202] g) Calculate the rate of temperature change inside the bubble at time t = k using equation (7).

[0203] h) Calculate the enthalpy difference of the bubble wall.

[0204] i) The rate of change of bubble pressure is obtained by differentiating equation (1) with respect to time t.

[0205] j) Taking the derivative of the enthalpy difference with respect to time t, we get...

[0206] k) Calculate the rate of change of the bubble wall velocity at time t = k using equation (10). The acceleration of the bubble wall;

[0207] l) To Find the derivative with respect to time t to obtain...

[0208] 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:

[0209] 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;

[0210] o) Repeat steps (a) to (n) until t > t max ;

[0211] p) Calculate the far-field wavelet sound pressure of the air gun, including virtual reflections from the sea surface:

[0212] 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 2 The different capacities of the air gun sub-waves are shown.

[0213] 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 3 As shown.

[0214] Step 4: Calculate Δt based on the statistical results of ti obtained in Step 3. i ;

[0215] Step 5: Based on the set initial conditions, perform a wide-pulse wavelet air gun array simulation. Figure 4 This is a plan view of the air gun array provided in this embodiment of the invention; the specific process is as follows: the air gun array has a total of 39 guns, of which 33 are working guns. There are 6 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). The Δt calculated in step 4... i The delayed excitation times for air guns of different capacities are as follows: no delay for 45 cu.in and 70 cu.in air guns; 1.0 ms delayed excitation for 100 cu.in and 150 cu.in air guns; and 2.0 ms delayed excitation for 250 cu.in air guns. The array is submerged at a depth of 6 m, and the cable is submerged at a depth of 8 m.

[0216] Step 6: Perform spectral analysis on the wide pulse wavelet according to the Fourier transform to obtain the wide pulse wavelet diagram shown in Figure 5(a) and the spectrum diagram shown in Figure 5(b); in the figure, bar m is the pressure in the chamber of the bubble generated by the air gun.

[0217] To better demonstrate the technical advantages of this invention, a comparison was made with the actual air gun array wavelet in a certain block of the Bohai Sea, resulting in the time-pressure pulse relationship diagram shown in Figure 6(a) and the frequency-power relationship diagram shown in Figure 6(b).

[0218] pass Figures 6(a)-6(b) Neutron wave comparison shows that, after adopting the method of this invention, the bandwidth of the obtained air gun wavelet is broadened, and the low-frequency energy in the spectrum is enhanced. The conventional array is an actual air gun array used in a certain block of the Bohai Sea, array number 718_4040_7_66-air. The array used in this invention is an optimized version of this array, and the array designed in this invention is numbered 718_4040_7_66-air-broad pulse-3.

[0219] Application Example 2

[0220] This invention also provides a method for high-precision full-waveform wavefield imaging using a obtained wide-pulse wavelet. The specific method for this full-waveform wavefield imaging includes velocity field data from the Marmousi model, the wide-pulse wavelet constructed in this invention, and a calculation method for wavefield imaging.

[0221] The velocity field data of the Marmousi model are as follows: Figure 7 As 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.

[0222] 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.

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

[0224] Figure 8(a) is a conventional air gun wavelet wave field imaging (71_4040_7_66-air) provided by an embodiment of the present invention;

[0225] Figure 8(b) is a wide-pulse wavelet wavefield imaging (71_4040_7_66-air-broad pulse-3) constructed using the present invention, provided by an embodiment of the present invention;

[0226] The conventional array is an actual air gun array used in a certain block of the Bohai Sea, with the array number 718_4040_7_66-air. The array used in this invention is an optimized version of this array, and the array designed in this invention is numbered 718_4040_7_66-air-broad pulse-3.

[0227] pass Figures 8(a)-8(b) It can be seen that the wave field imaging effect achieved by using the wide pulse wavelet constructed by the present invention is better, specifically, the energy is transmitted to a deeper depth and a wider width, and the structure of the medium and deep buried hills and inner regions is more clearly depicted.

[0228] 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 frequency band of an air gun source by constructing a wide pulse wavelet through delayed excitation, characterized in that, The method includes the following steps: S1. Simulate gas gun wavelets of different capacities based on the van der Waals nonideal gas wavelet model and set the initial conditions of the model. S2. Execute the simulation process according to the initial conditions of the set model; 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. f ; S4. Based on the simulation results, calculate the difference between the time from excitation to reaching the peak of the main pulse and the minimum time t0 for air guns of different capacities. ; S5, calculate the results As the delayed excitation time of air guns of different capacities in the air gun array, the air gun wavelet simulation is then performed to generate the air gun array wavelet with a wide pulse shape. S6. Perform spectral analysis on the obtained air gun array wavelet.

2. The method for broadening the frequency band of an air gun source by constructing a wide pulse wavelet through 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 van der Waals constants. , , For effective thermodynamic temperature, It is a universal gas constant. For gas mass, For volume, Air gun pressure; Effective temperature Depends on the high-pressure gas in the chamber: （2） In the formula, , Water temperature; According to the law of conservation of energy, the energy gained from heat transfer and mass transfer within the bubble is 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. and These are specific heat capacity at constant pressure and specific heat capacity at constant volume. It is the heat transfer rate through the bubble wall. The unit time interval for the bubble wall movement. This refers to the heat transferred from the bubble to its surroundings per unit time interval. This represents the decrease in the internal energy of the bubble per unit time. This represents the change in bubble volume per unit time. The heat transfer coefficient is the change in the mass of the substance inside the bubble per unit time. The bubble heat loss rate was determined by fitting the model with experimental data as follows: （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 its temperature and volume: （5） The total differential equation is expressed as: （6） Furthermore, the first law of thermodynamics can be transformed into: （7） In the formula, , The molar heat capacity under constant pressure, The rate of change of the amount of gaseous substance; The throttling constant of air guns with different capacities is related to the size of the air chamber, and 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; at any given time, the gas flow rate through the air gun port 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, the throttling constant. , air chamber capacity, The amount of matter in the gas inside the chamber. It's the air gun pressure. It is bubble pressure; 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 expression for the vertical rising velocity of the bubble during the bubble's ascent 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. This refers to the air gun depth; at a distance of 1m from the air gun, the air gun wavelet signal is represented as: （13） 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: （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 effect of the bubble on the first The hydrostatic pressure disturbance of the first bubble, and the first The effect of the bubble on the first Delay and pressure characteristics of each bubble on a distance scale: （15） In the formula Indicates the first The bubble and the first The spacing between bubbles.

3. The method for broadening the frequency band of an air gun source by constructing a wide pulse wavelet through delayed excitation according to claim 1, characterized in that, In step S1, the initial conditions of the model are set as follows: 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 an air gun source by constructing a wide pulse wavelet through delayed excitation according to claim 1, characterized in that, In step S2, the simulation process is performed according to the set initial conditions of the model, 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 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 are 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 frequency band of an air gun source by constructing a wide pulse wavelet through delayed excitation according to claim 1, characterized in that, In step S3, the time t from excitation to the peak value of the main pulse for gas gun wavelets of different capacities is statistically analyzed. f This includes: statistically calculating the time t it takes for the main pulse to reach its peak value after firing a gas gun with capacities of 45 cu.in, 70 cu.in, 100 cu.in, 150 cu.in, and 250 cu.in. f .

6. The method for broadening the frequency band of an air gun source by constructing a wide pulse wavelet through delayed excitation according to claim 1, characterized in that, In step S4, the difference between the time from excitation to reaching the peak of the main pulse and the minimum time t0 is calculated for air guns of different capacities. The purpose is to calculate the time difference between the time it takes for a gas 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 a gas gun with a capacity of 45 cu.in to reach the peak of the main pulse. .

7. The method for broadening the frequency band of an air gun source by constructing a wide pulse wavelet through delayed excitation according to claim 1, characterized in that, In step S5, the generation of the wide pulse pattern of the air gun array sub-wavelet is 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. The single gun capacity and number of guns are 45 cu.in, 70 cu.in, 100 cu.in, 150 cu.in and 250 cu.in, respectively.

8. The method for broadening the frequency band of an air gun source by constructing a wide pulse wavelet through delayed excitation according to claim 1, characterized in that, In step S6, the spectral analysis of the obtained air gun array wavelet 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 of -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.

9. A high-capacity air gun, comprising the method described in any one of claims 1-8 for widening the air gun source frequency band by constructing a wide pulse wavelet through delayed excitation.

10. The application of the method for widening the air gun source bandwidth by constructing a wide pulse wavelet through delayed excitation as described in any one of claims 1-8 in a broadband three-dimensional observation system for marine field, as well as in marine geological survey and oil and gas exploration equipment.

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