Patent ID: 11892578
Assignee: CHINA UNIVERSITY OF PETROLEUM (EAST CHINA)
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 0:
1. A seismic imaging method, comprising:
(S100) collecting seismic data comprising seismic source type, seismic source dominant frequency, location of a shot point, maximum tectonic angle, a set temporal sampling interval, a size of a velocity model, and a spatial interval;
(S200) extracting a common shot point gather from the seismic data; converting the common shot point gather to a time-space domain common offset gather according to the location of the shot point and a location of a receiver point; and converting time-space domain common offset seismic data in the time-space domain common offset gather from time-space domain to frequency-wavenumber domain by using Fourier transform to obtain frequency-wavenumber domain common offset seismic data;
(S300) calculating a plurality of wave propagation angles of a plurality of grid points of the velocity model based on the frequency-wavenumber domain common offset seismic data through the following equation:, θ
   =
   
    arctan
    ⁡
    (
    
     |
     
      
       ∂
       p
      
      
       ∂
       x
      
     
     |
     /
     |
     
      
       ∂
       p
      
      
       ∂
       z
      
     
     |
    
    )
   
  
  ,
 

wherein θ represents the wave propagation angles; ∂p/∂x represents a partial derivative of a seismic wavefield in x direction; and ∂p/∂z represents a partial derivative of the seismic wavefield in z direction; and
dividing an imaging region into a first region and a second region based on the plurality of wave propagation angles, wherein a wave propagation angle of the first region is smaller than a wave propagation angle of the second region;
(S400) calculating a plurality of optimized constant coefficients corresponding to the first region and the second region according to the following equation:, J
   =
   
    
     ∫
     0
     1
    
    
     
      ∫
      0
      φ
     
     
      
       
        (
        
         
          
           1
           -
           
            
             
              k
              x
             
             ¯
            
            2
           
          
         
         +
         n
         -
         1
         +
         
          
           (
           
            n
            -
            1
           
           )
          
          ⁢
          
           
            c
            ⁢
            
             
              
               k
               x
              
              ¯
             
             2
            
           
           
            a
            +
            
             b
             ⁢
             
              
               
                k
                x
               
               ¯
              
              2
             
            
           
          
         
         -
         
          
           
            n
            2
           
           -
           
            
             
              k
              x
             
             ¯
            
            2
           
          
         
        
        )
       
       2
      
      ⁢
      
       d
       ⁢
       θ
       ⁢
       dn
      
     
    
   
  
  ;
 

wherein J is an objective function; θ represents the wave propagation angle; n is a medium refractive index; a, b and c represent the plurality of optimized constant coefficients; kx represents wavenumber in x direction; kx represents normalized wavenumber in x direction, and kx=kx/k0; k0 represents wavenumber based on background velocity; and φ is a set maximum imaging angle;
(S500) constructing a rational function-approximation dispersion relation based on heterogeneity of a real underground medium; and substituting the rational function-approximation dispersion relation into a frequency-wavenumber domain Fourier wavefield continuation fundamental equation to obtain a frequency-wavenumber domain wavefield continuation equation, expressed as:, P
    ⁡
    (
    
     
      k
      x
     
     ,
     
      z
      +
      
       Δ
       ⁢
       z
      
     
    
    )
   
   =
   
    
     {
     
      
       
        
         
          
           (
           
            1
            -
            α
           
           )
          
          ⁢
          
           exp
           [
           
            
             ik
             0
            
            ⁢
            Δ
            ⁢
            
             z
             ⁡
             (
             
              n
              -
              1
             
             )
            
           
           ]
          
         
         +
        
       
      
      
       
        
         α
         ⁢
         
          exp
          [
          
           i
           ⁢
           
            k
            0
           
           ⁢
           Δ
           ⁢
           
            z
            ⁡
            (
            
             
              2
              ⁢
              n
             
             -
             2
            
            )
           
          
          ]
         
        
       
      
     
     }
    
    ⁢
    
     p
     ⁡
     (
     
      
       k
       x
      
      ,
      z
     
     )
    
    ⁢
    
     exp
     ⁡
     (
     
      i
      ⁢
      
       k
       z
      
      ⁢
      
       Δ
       ⁢
       z
      
     
     )
    
   
  
  ;
 

wherein P(kx,z+Δz) represents wavefield information at a depth of z+Δz; kz represents wavenumber in z direction; p(kx,z) represents wavefield information at a depth of z; α is an intermediate parameter variable, represented by, α
   =
   
    
     
      ck
      x
      2
     
     _
    
    
     a
     +
     
      
       bk
       x
       2
      
      _
     
    
   
  
  ;
 

 i represents an imaginary number; and Δz represents a spatial sampling interval along a depth direction; and
substituting the plurality of optimized constant coefficients obtained in step (S400) into the intermediate parameter variable α of the frequency-wavenumber domain wavefield continuation equation, and processing the frequency-wavenumber domain common offset seismic data by using the frequency-wavenumber domain wavefield continuation equation thereby obtaining a plurality of images at different depths and frequencies;
(S600) integrating the plurality of images to obtain a plurality of integrated images; and transforming the plurality of integrated images to a spatial domain by using inverse Fourier transform to obtain a plurality of common offset imaging profiles; and
(S700) superposing the plurality of common offset imaging profiles to obtain a seismic image.