CN-115877440-B - Method for expanding wavelet band of air gun focus by stereo arrangement and delayed excitation and application

CN115877440BCN 115877440 BCN115877440 BCN 115877440BCN-115877440-B

Abstract

The invention belongs to the technical field of air gun seismic sources in shallow sea seismic exploration, and discloses a method for widening wavelet bands of an air gun seismic source through three-dimensional arrangement and delayed excitation and application thereof. The method comprises the steps of calculating the sinking depth of air guns with different capacities and the time for reaching a main pulse peak value after the air guns are excited, then adjusting the sinking depth of the air guns with different capacities based on the calculated time, adjusting the excitation time of the air guns with different capacities, enabling the time offset corresponding to the main pulse peak value of each air gun with different capacities in the air gun array, finally constructing a sharp pulse source wavelet with narrower main pulse waveform of the air gun array, and realizing the expansion of the source wavelet frequency band. According to the invention, spike wavelets are constructed by adjusting the sinking depth and the excitation time of air guns with different capacities, virtual reflection is suppressed, the purpose that the frequency band of the air gun array is expanded to low frequency on the basis of guaranteeing high frequency is realized, and finally, the air gun seismic source with rich high and low frequency and strong energy downloading capability aiming at the middle-deep geological target is obtained.

Inventors

HUANG JIANGBO
LV DINGYOU
ZHANG ZHONGQIAO
HE DIANBO
WANG ZHILIANG
ZHANG CAN
YAO YONGQIANG

Assignees

中海石油(中国)有限公司
中海石油（中国）有限公司天津分公司

Dates

Publication Date: 20260505
Application Date: 20221223

Claims (10)

1. A method for widening the wavelet band of air gun source through stereo arrangement and delay excitation is characterized by comprising the steps of calculating the sinking depth of air guns with different capacities and the time for reaching the peak value of main pulse after the air guns are excited, then adjusting the sinking depth of the air guns with different capacities based on the calculated time, and simultaneously adjusting the excitation time of the air guns with the part, so that the time offset corresponding to the peak value of the main pulse of each air gun with different capacities in an air gun array is adjusted, finally constructing the sharp pulse source wavelet with narrower main pulse waveform of the air gun array, and realizing the expansion of the wavelet band of the source, and specifically comprises the following steps: S1, simulating air gun wavelets with different capacities according to a Van der Waals nonideal air gun wavelet model, and setting initial conditions; s2, executing a simulation process according to the initial conditions set in the step S1; S3, analyzing the simulated air gun wavelets, and counting the time t i from the excitation to the main pulse peak value of the air gun wavelets with different capacities; s4, according to the simulation result, the smaller the capacity is, the smaller the t i is, the supposing the minimum t i is t 0 , and the difference value between the time from excitation to main pulse peak value and t 0 of air guns with different capacities is calculated , ; S5, taking 1/2 calculated in the step S4 As the delayed firing time of air guns of different capacities in an air gun array, the depth of sinking of the part of air guns is reduced by 1/4 C is the gas velocity, and then the air gun wavelet simulation is carried out; s6, performing spectrum analysis on the air gun array wavelet obtained in the step S5.
2. The method of widening the airgun source wavelet band by stereo ranging and delayed excitation according to claim 1, wherein in step S1, the equation of the van der waals nonideal gas gun wavelet model is expressed as: (1) wherein a and b are van der Waals constants, T g is the effective thermodynamic temperature, R g is the universal gas constant, m g is the gas mass, and V g is the volume; The effective temperature T g depends on the high pressure gas within the chamber: (2) In the formula, ; In the air gun excitation process, according to the law of conservation of energy, energy obtained by heat transmission loss of air bubbles and mass transfer of air bubble substances must be balanced with the change of the internal energy of the air bubbles, and then: (3) In the formula, Is the temperature of the air bubble and the temperature of the air bubble, Is the pressure of the air bubbles and, Is the mass of the gas in the bubble, Represents the internal energy of the air bubble, Is the specific heat capacity of constant pressure, Is the heat transfer rate and heat transfer coefficient through the bubble wall Is determined by fitting a model to the experimental data, and the bubble heat loss rate is expressed as: (4) In the formula, Is the bubble temperature And ambient water temperature The temperature difference between the two is calculated, Is the bubble radius, and the internal energy of the non-ideal gas is a function of gas temperature and volume using the van der waals non-ideal gas equation: (5) the full differential equation is expressed as: (6) The first law of thermodynamics translates into: (7) In the formula, Rate of change of the amount of gaseous substance Throttle constant , Is the capacity of the air chamber, Is the mass of the gas in the gas chamber, Is the pressure of the air gun and the air pressure of the air gun, Is the bubble pressure; the throttle constants of air guns of different capacities are only related to the size of the air chamber, expressed as: (8) In the formula, Is a port throttle constant independent of capacity, The flow rate of the gas passing through the port of the air gun depends on the pressure difference inside and outside the air gun in any given time according to the measurement and calculation results, and the release rate of the gas is expressed as follows: (9) In the formula, Is the amount of gaseous material released into the bubbles, Is the total amount of gas in the gas chamber, Is the ratio of the amount of gas in the bubble to the total amount; The equation of motion of the bubble wall is expressed as: (10) In the formula, Is the radius of the air bubble, And The velocity and acceleration of the bubble wall respectively, Is the velocity of the sound wave in the fluid medium, Is the enthalpy difference of the bubble wall, Is the static water density at infinity, Is the pressure of the air bubbles and, Is hydrostatic pressure at infinity, the hydrostatic pressure of the bubble changes in the process of rising of the bubble due to buoyancy, and the expression of the vertical rising speed of the bubble in the process of rising of the bubble is as follows: (11) In the formula, Is the bubble depth, g is the gravitational acceleration constant, Is bubble radius, hydrostatic pressure The expression of (2) is: (12) In the formula, Is a standard atmospheric pressure of air and, Is the depth of the air gun; at 1m from the air gun, the air gun wavelet signal is expressed as: (13) At low frequency, the interaction between bubbles is not negligible, the interaction between bubbles is the adjustment of hydrostatic pressure of fluid, the interaction between bubbles can change the pressure around the bubbles, the bubbles are a point relative to the earthquake wavelength, the pressure field around any arbitrary bubble is superposition of hydrostatic pressure plus time-varying pressure field generated by the bubbles, and the effective hydrostatic pressure at each bubble of j is; (14) In the formula, Is the hydrostatic pressure of the water, Is the sum of the pressure contributions of all other air guns in the air gun array, Is the first Hydrostatic pressure disturbance caused by the bubble to the j-th bubble, and Delay to the j-th bubble and pressure characteristics on a distance scale caused by the individual bubbles: (15) In the formula, Represents the j-th bubble Bubble spacing between individual bubbles.
3. The method for broadening the wavelet bands of an air gun source through stereo ranging and delayed excitation as defined in claim 1, wherein in step S1, the initial conditions specifically include: step 1.1, condition 1, initial value of air gun pressure Setting the working pressure; step 1.2, condition 2, initial temperature in the bubble is set to ; Step 1.3, condition 3 initial volume of bubbles An initial radius of ; Step 1.4, condition 4, initial velocity of bubble wall is ; Step 1.5, condition 5 bubble initial pressure The initial temperature is water temperature The initial mass in the bubble is ; And 1.6, setting the placement positions (x, y, z) of the air guns.
4. The method for widening the wavelet bands of the air gun source through stereo arrangement and delayed excitation according to claim 1, wherein in step S2, the simulation process is performed according to the initial conditions set in step S1, specifically: Step 2.1, inputting initial conditions of a Van der Waals nonideal gas gun wavelet model; step 2.2, starting the time cycle and calculating the bubble volume at time t=k ; Step 2.3, calculating the bubble pressure at the time t=k by using the equation (1), ; Step 2.4, calculating the heat loss rate of the bubbles through an equation (4), ; Step 2.5, calculating the release rate of the gas by an equation (9), ; Step 2.6, calculating The rate of change of the volume of the bubbles at the moment in time, ; Step 2.7, calculating by equation (7) The rate of change of temperature within the bubble at the moment, ; Step 2.8, calculating enthalpy difference of the bubble wall, ; Step 2.9, solving the equation (1) for time The differentiation of (c) yields the rate of change of bubble pressure, ; Step 2.10, enthalpy difference is calculated with respect to time Is obtained by a differentiation of (a) and (b), ; Step 2.11, calculation by equation (10) The rate of change of velocity of the bubble wall at the moment in time, Acceleration of the bubble wall; Step 2.12, pair , , , , , Solving for time Is obtained by a differentiation of (a) and (b), , , , , , ; Step 2.13, since the air gun wavelet simulation is an iterative process, the bubble wall radius, the bubble wall speed, the gas temperature and the mass of the gas in the bubble can be obtained through the second-order Taylor series expansion: , , , and ; step 2.14, expressing bubble pressure as a function of enthalpy, bubble wall velocity and bubble radius: , distance from the center of the bubble to the far field point; step 2.15, repeating steps (2.1) to (2.14) until ; Step 2.16, calculating far-field wavelet sound pressure of the air gun, including sea surface ghost reflection: , representing the reflection coefficient of the sea surface, It is the distance between the air gun and the hydrophone that, Is the distance between the sea surface mirror image of the air gun and the hydrophone, Is the air gun signal passing through And Is a time delay of (a) to (b).
5. The method for widening the wavelet bands of air gun seismic sources according to claim 1, wherein in step S4,  t i is calculated according to t i obtained by statistics in step S3, specifically, the difference between the time to reach the main pulse peak after the air gun with 70 cu.in/100 cu.in/150 cu.in/250 cu.in capacity is calculated and the time to reach the main pulse peak by the air gun with 45cu.in capacity is calculated 。
6. The method for widening the sub-wave band of the air gun source by stereo arrangement and delayed excitation according to claim 1, wherein in the step S5, the air gun array is specifically 39 guns in total, wherein 33 guns are operated, and 6 guns are emptied, and the total capacity is 4040cu.in.
7. The method for widening the wavelet band of the air gun source through stereo arrangement and delayed excitation according to claim 1, wherein in step S6, the spectrum analysis is performed on the wavelets of the air gun array in step S5, specifically comprising the steps of calculating a main pulse peak value, a ghost value and a bubble pulse peak value of the wavelets of the air gun array, performing the spectrum analysis on the wavelets through Fourier transform, taking the maximum amplitude-6 dB as a standard for judging the effective bandwidth, obtaining the effective bandwidth of the main pulse of the wavelets, and obtaining the main frequency of the main pulse of the wavelets.
8. A computer device comprising a memory and a processor, the memory storing a computer program that, when executed by the processor, causes the processor to perform the method of widening the air gun source wavelet band by stereo ranging and delayed activation as claimed in any one of claims 1-7.
9. An air gun source for deep geological target exploration in the ocean, which implements the method for widening the wavelet band of the air gun source through stereo arrangement and delay excitation according to any one of claims 1-7.
10. A marine hydrocarbon resource exploration apparatus incorporating an air gun source as claimed in claim 9 for use in the exploration of deep geological objects in the ocean, implementing the method of widening the sub-wave band of an air gun source by stereo ranging and delayed excitation as claimed in any one of claims 1 to 7.

Description

Method for expanding wavelet band of air gun focus by stereo arrangement and delayed excitation and application Technical Field The invention belongs to the technical field of air gun seismic sources in the shallow sea seismic exploration process, and particularly relates to a method for widening a wavelet band of an air gun seismic source through three-dimensional arrangement and delayed excitation and application thereof. Background In marine geological investigation and oil and gas resource exploration, an air gun source is key equipment in a marine seismic information acquisition system, and particularly, compared with other sources, the low-frequency energy of the air gun source is more suitable for exploration of deep geological targets in the ocean. As the exploitation of ocean oil and gas resources advances toward the middle-deep layer, the geological conditions are more and more complex, the requirements on the seismic acquisition precision and resolution are improved, and the air gun seismic source with rich low-frequency energy is more and more concerned. A large volume air gun can contribute more low frequency signals, but the bubble effect is significant. At present, the purposes of widening the wave band of a seismic source wavelet and improving the downloading capability of seismic waves for seismic exploration are achieved mainly by a multi-subarray plane and three-dimensional combination method at home and abroad by utilizing tuning and coherence technology, but high-frequency components are often enhanced, low-frequency components are not abundant, so that how to excite the seismic source wavelet with stronger low-frequency energy is a problem to be solved urgently in the field of geophysics. How to enrich low-frequency components and improve the penetrating power of the air gun focus wavelet is a focus to be improved based on the prior art. Through the above analysis, the problems and defects existing in the prior art are as follows: (1) In the prior art, spike wavelets are not constructed by setting the sinking depth of air guns with different capacities and adjusting the excitation time of the air guns with different capacities, and high-resolution and high-penetrating-capacity seismic source wavelets applicable to shallow sea deep geological target exploration cannot be generated. (2) The prior art can not realize the widening of the wavelet frequency band of the seismic source, and has poor detection effect on deep geological targets. Disclosure of Invention In order to overcome the problems in the related art, the disclosed embodiment of the invention provides a method for widening the wavelet band of an air gun source through three-dimensional arrangement and delayed excitation, which is used for a marine field broadband high-resolution three-dimensional observation system, exploration and acquisition of deep seismic reflection signals and is used for marine geological investigation and oil and gas resource exploration. The invention aims to construct spike wavelet by setting the sinking depth of air guns with different capacities and adjusting the excitation time of the air guns with different capacities, and finally, the high-resolution and high-penetrability seismic source wavelet suitable for shallow sea deep geological target exploration is generated. The technical scheme includes that the method for widening the wavelet bands of the air gun focus by three-dimensional arrangement and delayed excitation is adopted, the sinking depth of air guns with different capacities and the time for reaching the main pulse peak value after the air guns are excited are calculated, then the sinking depth of the air guns with different capacities is adjusted based on the calculated time, meanwhile, the excitation time of the air guns is adjusted, the time offset corresponding to the main pulse peak value of each air gun with different capacities in an air gun array is adjusted, finally, the sharp pulse focus wavelet with narrower main pulse waveform of the air gun array is constructed, and the expansion of the wavelet bands of the focus is realized, and the method specifically comprises the following steps: S1, simulating air gun wavelets with different capacities according to a Van der Waals nonideal air gun wavelet model, and setting initial conditions; s2, executing a simulation process according to the initial conditions set in the step S1; S3, analyzing the simulated air gun wavelets, and counting the time t i from the excitation to the main pulse peak value of the air gun wavelets with different capacities; S4, according to a simulation result, the smaller the capacity is, the smaller the t i is, the supposing that the minimum t i is t 0, and the difference delta t i,Δti＝ti-t0 between the time from excitation to main pulse peak of air guns with different capacities and t 0 is calculated; S5, taking 1/2 Deltat i calculated in the step S4 as the delay excitation time of air guns with differ