Process for Creating Image Gathers

Abstract

The process of obtaining seismic data includes deploying a seismic energy source and seismic receivers, actuating the source, and detecting seismic energy resulting therefrom at the receivers. The process further includes digitally sampling seismic energy detected at the receivers indexed with respect to time to form a plurality of traces and sorting the traces to form a plurality of shot gathers. In addition, the process includes applying a depth migration technique to the shot gathers to generate two images according to the cross-correlation imaging condition (I 0 ) and the gradient-based imaging condition (I 1 ) for each shot gather. A reflection angle (θ) or a general domain parameter (α) is computed at each subsurface position and the images are mapped according to the corresponding reflection angle or the general domain parameter to form common image gathers. Amplitude correction is applied to common image gathers and the images and common image gathers are stored on non-transitory computer-readable media.

1 . A process comprising:
 obtaining seismic data by deploying a seismic energy source and seismic receivers, actuating the source, and detecting seismic energy reflected from a plurality of subsurface positions resulting therefrom at the receivers;   forming a plurality of traces by digitally sampling the seismic energy detected at the receivers and indexing the seismic energy with respect to time;   sorting the traces to form a plurality of shot gathers;   applying a depth migration technique to the shot gathers to generate two images according to the cross-correlation imaging condition (I 0 ) and the gradient-based imaging condition (I 1 ) for each shot gather;   computing a reflection angle (θ) or a general domain parameter a at each subsurface position;   mapping the images according to the corresponding reflection angle or general domain parameter to form common image gathers;   applying amplitude correction to common image gathers; and   storing the images and common image gathers on non-transitory computer-readable media.   
     
     
         2 . The process of  claim 1 , wherein the step of applying a depth migration technique is performed using reverse-time migration. 
     
     
         3 . The process of  claim 1 , wherein the step of computing a reflection angle (θ) or a general domain parameter (α) at each subsurface position comprises computing the reflection angle at at least one subsurface position using the following formula:
   θ({right arrow over ( x )})=cos −1 ( I   1   /I   0 )
 
 
       wherein {right arrow over (x)} is an image point corresponding to the at least one subsurface position. 
     
     
         4 . The process of  claim 1 , wherein the step of computing the reflection angle (θ) or a general domain parameter (α) comprises computing the general domain parameter using the following formula: 
       
         
           
             
               α 
               = 
               
                 
                   
                     
                       c 
                       0 
                       2 
                     
                     
                       
                         c 
                         s 
                       
                        
                       
                         c 
                         r 
                       
                     
                   
                    
                   
                     cos 
                      
                     
                       ( 
                       θ 
                       ) 
                     
                   
                 
                 = 
                 
                   
                     I 
                     1 
                   
                   / 
                   
                     I 
                     0 
                   
                 
               
             
           
         
       
       wherein c 0  is the phase velocity along a symmetry axis, and c s  and c r  are the phase velocities of the source and receiver wave fields respectively. 
     
     
         5 . The process of  claim 1 , further comprising, prior to the step of computing a reflection angle (θ) or a general domain parameter (α), the step of:
 converting the images to reflector dip angle domain. 
 
     
     
         6 . The process of  claim 5 , further comprising, after the step of mapping the images according to the corresponding reflection angle or the general domain parameter, the step of:
 transforming the images to space domain.   
     
     
         7 . The process of  claim 1 , further comprising, after the step of computing a reflection angle (θ) or a general domain parameter (α), the steps of:
 mapping the source illumination to the reflection angle domain; and 
 applying illumination compensation to common image gathers. 
 
     
     
         8 . The process of  claim 1 , further comprising generating a model of a subsurface formation including the subsurface positions based at least in part on the images or common image gathers of the images and common image gathers.