Velocity Analysis Of Common Shot Gathers Under The Elliptic Development Method

Seismic-wave propagation velocity is one of the most important parameters in seismic data processing and interpretation. Stack velocity analysis is the conventional method to acquire velocity information. However, it has the assumption of horizontally layered media. If the media is complex, there will be the phenomenon of dispersion of the common reflection point. So the stack profiles that obtained from this method are not strictly zero offset profiles, and post-stack migration will lead to great error. Therefore, this paper developed a velocity analysis method of common shot gathers.Among numerous methods that access to zero offset profiles, the elliptic development of reflections has its original advantages. It abandons the idea of common midpoint stack. Utilizing the elliptic development transformation, we can obtain images from common shot gathers. Based on the theory of the elliptic development of reflections, this paper abandons the constraints of horizontally layered media, and proposes a new method for velocity analysis of common shot gathers, and gives the corresponding workflows. First, according to the selected velocity range, by adopting the elliptic development of reflections and coherence stack, the zero offset stack profiles can be obtained for every velocity from the initial velocity to the maximum velocity based on the common shot gathers. Then, we sort the zero offset stack profiles to form the velocity spectrum of the common normal emergence point, and determine the root-mean-square (RMS) velocity for every normal emergence point according to the maximum energy criteria. Further, based on the elliptic development, the zero offset stack profiles can be obtained by using the picked-up RMS velocity. Moreover, by testing the influence of different model parameters on this method, we summarize the announcements of velocity analysis, and test the feasibility of this method.This velocity analysis method adopts the original common shot gathers. So, it reserves more useful information, and doesn't need to sort any kinds of velocity analysis gathers in advance. Also, it avoids the phenomenon of dispersion of the common reflection point. The algorithm was applied to synthetic records and the real data, the results show that this approach can produce true zero offset profiles and velocity information which has nothing to do with the dip of reflectors, and have satisfactory practical application effect.