Method for Determination of Diffractor Locations at Sea Bottom for the Purpose of Attenuating Such Energy

Abstract

Coherency analysis, such as semblance scan or stacking amplitude, is used to locate diffractors. Once the diffractors are located, noise energy originating from the diffractors is minimized. Locations of each diffractor are determined by comparing the lateral coherency of the received amplitudes that each assumed diffractor position generates.

1 . A method of determination of seabottom diffractor location utilizing traces of a recorded 3-D marine seismic survey with one or more cables, comprising the steps of:
 Selecting coordinate boundary;   Calculating lateral coherency values, wherein the coherency value is calculated using amplitudes of traces at calculated travel times; and   Determining seabottom diffractor location in the coordinate boundary area using the coherency values.   
   
   
       2 . A method of determination of diffractor location utilizing traces of a recorded 3-D marine survey with one or more cables, comprising the steps of:
 Selecting coordinate boundary;   Calculating lateral coherency values, wherein the coherency value is calculated using amplitudes of traces at calculated travel times;   Determining diffractor location in the coordinate boundary area using the coherency values; and wherein said Steps B and C include the steps of:   Selecting scan increments; and   Searching local maxima in the scan increment identified from said coherency value calculation to determine the locations of the diffractors.   
   
   
       3 . The method of  claim 2  wherein Step B includes smoothing in coherency calculations using multiple time samples and there is included the step of:
 Rejecting the diffracted energy for each selected diffractor location.   
   
   
       4 . The method of  claim 3  wherein Step B has included the step of accomplishing the smoothness of the coherency values by the use of multiple time samples. 
   
   
       5 . The method of  claim 4  wherein more than one time sample is used and a matrix of numbers is created for use in coherency calculations. 
   
   
       6 . The method of  claim 4  wherein the number of time samples chosen is arbitrary. 
   
   
       7 . The method of  claim 4  wherein Step A includes the step of constituting a test grid and semblance is used for the coherency calculations for all points on the grid and there is included the step of calculating semblance using one or many time samples on each trace. 
   
   
       8 . The method of  claim 7  wherein the fold value at each location is used to accomplish normalizing. 
   
   
       9 . The method of  claim 8  wherein the maximum fold value can be used for normalizing. 
   
   
       10 . The method of  claim 2  wherein the scan increments are chosen from any random distance value. 
   
   
       11 . The method of  claim 10  wherein the scan increments are 25 m in both x and y directions. 
   
   
       12 . The method of  claim 10  wherein the scan increments are as low as 5 m and as high as 100 m. 
   
   
       13 . The method of claim I wherein in Step B at least one of the traces that a diffractor has contaminated is used in the coherency calculations. 
   
   
       14 . 
   
   
       15 . The method of  claim 1  wherein there are boundary values of the boundary area and the chosen boundary values, X min , X max , Y min , Y max , are extended by the amount that a seismic wave can travel in the recording time. 
   
   
       16 . The method of  claim 1  wherein the calculated travel times are in the recorded range of said survey. 
   
   
       17 . The method of  claim 1  wherein the one or more cables per shot and one or more shots are used in the coherency value calculations. 
   
   
       18 . The method of  claim 1  wherein if the calculated travel time falls between two samples having a coarse increment between them of the recorded trace, the value of the amplitude is interpolated. 
   
   
       19 . The method of  claim 1  wherein semblance is used for the coherency calculations. 
   
   
       20 . The method of  claim 2  wherein semblance is used for the coherency calculations. 
   
   
       21 . The method of  claim 1  wherein the size of the surveyed area to be searched for diffractors is selected as necessary from the 3-D marine survey parameters. 
   
   
       22 . The method of  claim 1  wherein there is included the step of creating a plot of the coherency values with relation to their physical location in the survey. 
   
   
       23 . A method of determination of diffractor location utilizing traces of a recorded 3-D marine survey with one or more cables, comprising the steps of:
 Selecting coordinate boundary;   Calculating lateral coherency values, wherein the coherency value is calculated using amplitudes of traces at calculated travel times; and   Determining diffractor location in the coordinate boundary area using the coherency values;   wherein the determining of the actual locations of the diffractors is determined by requiring that a local maxima point on a coherency plot be the largest amplitude in a space (x, y) window.   
   
   
       24 . The method of  claim 23  wherein the window size is 100 m by 100 m. 
   
   
       25 . 
   
   
       26 . The method of  claim 23  wherein the window size is calculated by inputting a window size in distance, which is then converted into a window size in grid points. 
   
   
       27 . The method of  claim 23  wherein there is included the step of comparing the coherency value inside the window to determine the largest amplitude in the neighborhood. 
   
   
       28 . The method of  claim 27  wherein a point of coherency value is chosen as local maxima if it is greater than its neighbors. 
   
   
       29 . The method of  claim 23  wherein said window is then moved by a single point in either the x or y direction until every point on the grid has been compared to its neighbors. 
   
   
       30 . 
   
   
       31 . The method of  claim 1  wherein there is included the step of using flattening techniques once the diffractors are located. 
   
   
       32 . The method of  claim 31  wherein noise rejection is included in the steps of  claim 31  and is accomplished through the use of a tool for removing events that contaminate data. 
   
   
       33 . The method of  claim 32  wherein noise rejection is accomplished through FK filter. 
   
   
       34 . The method of  claim 32  wherein noise rejection is accomplished through regular and high-resolution radon filter. 
   
   
       35 . The method of  claim 32  wherein noise rejection is accomplished through eigenimage filter. 
   
   
       36 . The method of  claim 1  wherein there is included the steps of flattening and event suppressing for the found diffractor locations. 
   
   
       37 . The method of  claim 1  wherein the coherency values are calculated by stacking amplitude. 
   
   
       38 . The method of  claim 1  wherein in Step A the coordinate boundary area is the area necessary for evaluating one shot. 
   
   
       39 . The method of  claim 1  wherein in Step A is the step of selecting coordinate boundary area of surveyed data of a recorded range. 
   
   
       40 . The method of  claim 39  wherein the data of the whole survey area is used. 
   
   
       41 . A method of determination of diffractor location utilizing a recorded 3D marine survey with one or more cables, comprising the steps of:
 Selecting coordinate boundary area;   Selecting scan increments;   Calculating semblance values; and   Searching local maxima in the scan increment identified from said semblance value calculation to determine the locations of the diffractors.   
   
   
       42 . A method of determination of diffractor location utilizing a recorded 3D marine survey with one or more cables, comprising the steps of:
 Selecting coordinate boundary area;   Selecting scan increments;   Calculating stacking amplitudes values; and   Searching local maxima in the scan increment identified from said stacking amplitudes value calculation to determine the locations of the diffractors.   
   
   
       43 . A method of determination of a diffractor location utilizing a recorded 3-D marine survey with one or more cables, comprising the steps of:
 Selecting boundary area;   Calculating coherency values;   Determining diffractor location in the boundary area using the coherency values.   
   
   
       44 . A method of determination of diffractor location utilizing traces of a recorded 3-D marine survey with one or more cables, comprising the steps of:
 Selecting coordinate boundary area;   Selecting scan increments;   Calculating coherency values, wherein the coherency value is calculated using amplitudes of traces at calculated travel times; and   Searching local maxima in the scan increment identified from said coherency value calculation to determine the locations of the diffractors.   
   
   
       45 . The method of  claim 44  wherein there is included the step of:
 Rejecting the diffracted energy for each selected diffractor location.   
   
   
       46 . The method of  claim 44  wherein there is included the step of smoothing in coherency calculations. 
   
   
       47 . A method of determination of sea bottom diffractor location utilizing traces of a recorded 3-D marine survey with one or more cables, comprising the steps of:
 Selecting coordinate boundary in the sea bottom;   Calculating coherency values, wherein the coherency value is calculated using amplitudes of traces at calculated travel times; and   Determining diffractor location in the coordinate boundary area using the coherency values.