Seismic data processing method and system for migration of seismic signals incorporating azimuthal variations in the velocity

Abstract

A method and system for seismic data processing utilizes azimuthal variations in the velocity of seismic signals. The system and method utilizes a plurality of seismic energy sources that are located at known positions at the surface of the earth. The seismic energy sources generate seismic signals that propagate downward into the earth. Some of the seismic signals are reflected and diffracted by various sub-surface layers and are returned to the surface of the earth. The returned seismic signals are received by a plurality of receivers. The method includes the step of determining the distance from an energy source to an image point. A fast travel time of the seismic signal from the energy source to the image point is determined, and a slow travel time of the seismic signal from the energy source to the image point is determined. The azimuth angle between the energy source and the surface location of the image point is calculated. A first travel time of the seismic signal traveling from the energy source to the image point is calculated. A second travel time of the seismic signal traveling from the image point to the seismic receiver is calculated. The total travel time is calculated by adding the first and second travel time. The amplitudes from the recorded signal at the total travel time are phase adjusted and added into the output image at the image point. The foregoing steps are repeated for a plurality of image points beneath the surface of the earth and the total travel time is calculated.

1 . A method of seismic data processing for migration that incorporates variations in velocity with azimuth, the method utilizing a plurality of seismic energy sources and seismic receivers located at known positions at the surface of the earth and a plurality of image points located at predetermined depths beneath the surface, each seismic energy source generating one or more seismic signals that propagate into the earth and return to the surface where the seismic signals are received by the seismic receivers, the method comprising the steps of:
 determining the distance from the energy source to the surface location of the image point;   determining the fast travel time of the seismic signal from the energy source to the image point;   determining the slow travel time of the seismic signal from the energy source to the image point;   determining the azimuth angle between the energy source and the surface location of the image point;   determining a first azimuth dependent travel time for the seismic signal traveling from the energy source to the image point using the fast travel time, the slow travel time, the azimuth angle of the fast velocity direction, and the azimuth angle of the energy source location to the image point location on the surface;   determining the distance from the receiver to the surface location of the image point;   determining the fast travel time of the seismic signal from the receiver to the image point;   determining the slow travel time of the seismic signal from the receiver to the image point;   determining the azimuth angle between the receiver and the surface location of the image point; and   determining a second azimuth dependent travel time for the seismic signal traveling from the receiver to the image point using the fast travel time, the slow travel time, the azimuth angle of the fast velocity direction, and the azimuth angle of the receiver location to the image point on the surface.   
   
   
       2 - 10 . (canceled) 
   
   
       11 . A system for seismic data processing by incorporating the azimuthal variations of the velocity of seismic signals, comprising:
 a computer comprising;   a processor;   a memory coupled to the processor;   an input device coupled to the processor and adapted to receive seismic data and to provide the seismic data to the processor,   a program code stored in the memory and executable by the processor to process the seismic data by performing the following steps:   determining the distance from an energy source to an image point;   determining the fast travel time of the seismic signal from an energy source to an image point;   determining the slow travel time of the seismic signal from the energy source to the image point;   determining the azimuth angle between the energy source and the surface location of the image point,   determining a first azimuth dependent travel time of the seismic signal traveling from the energy source to the image point;   determining the distance from a receiver to an image point;   determining the fast travel time of the seismic signal from a receiver to an image point;   determining the slow travel time of the seismic signal from the receiver to the image point;   determining the azimuth angle between the receiver and the surface location of the image point,   determining a second azimuth dependent travel time of the seismic signal traveling from the image point to the receiver;   calculating the total travel time by adding the first and second azimuth dependent travel times;   summing the amplitudes from the input signals at the total travel time, wherein the signals are phase adjusted according the Kirchhoff imaging criteria and then summed into the output image at the image point; and   repeating the foregoing steps for a plurality of image points beneath the surface of the earth and calculating the total travel time for the plurality of image points.   
   
   
       12 . The system of  claim 11 , wherein the fast travel time is calculated using the distance from the energy source to the surface location of the image point, the travel time from the surface location of the image point to the image point, and a fast velocity table. 
   
   
       13 . The system of  claim 11 , wherein the slow travel time is calculated using the distance from the energy source to the surface location of the image point, the travel time from the surface location of the image point to the image point, and a slow velocity table. 
   
   
       14 . The system of  claim 11 , wherein the azimuthal angle between the energy source and the surface location of the image point and the azimuthal angle between the energy source and the surface location of the image point are calculated using the respective coordinates. 
   
   
       15 . (canceled) 
   
   
       16 . A method of seismic data processing, comprising the steps of:
 determining the azimuthal variations in the velocity of seismic signals, the seismic signals propagating from one or more seismic energy sources to one or more image points and to one or more seismic receivers;   determining the travel times of the seismic signals using the azimuthal variations in the velocity of the seismic signals, and using the travel times in migration methods.   
   
   
       17 . The method of  claim 16 , wherein the travel times are determined using an elliptical function when provided a fast velocity and a slow velocity. 
   
   
       18 . A method of seismic data processing, comprising the steps of:
 determining the azimuthal variations in the velocity of seismic signals, the seismic signals propagating from one or more seismic energy sources to one or more image points and to one or more seismic receivers;   calculating the travel times of the seismic signals using the azimuthal variations in the velocity of the seismic signals;   using the travel times in migration methods and generating image of the seismic signals using the travel times.