Common Shot Gather Velocity Analysis Based On The Elliptic Development Method

It is well known that zero-offset section is very important in seismic data processing and interpretation, which is also the objective of conventional CMP (Common Midpoint) stack. There are many methods to obtain zero-offset section The paper briefly outlines several main stack methods (NMO (Normal Moveout) stack, DMO(Dip Moveout)stack, prestack migration, CRS(Common Reflection Surface) stack, et al.), and introduces their respective advantages and disadvantages. Then, the ellipse evolving common reflection point stack is brought in with innovation and distinction, which abandons conventional CMP gathering and NMO stack. Based on ray theory, the ellipse evolving stack adopts the technology of ellipse evolving and envelops intervening and stacking to image. When the media were homogeneous, velocity calculated by ellipse evolving is the real velocity of media, as well as the stack section is the real zero-offset section.?We can get correct subsurface image for strata-media using conventional CMP stack imaging method. But if there exists complex structure, such as dipping reflectors, including in the subsurface, image that is imaged by conventional CMP stack method would depart from true subsurface structure, and then post-stack migration is necessary to move dipping reflector into their true subsurface positions. If geological structure is more complex, stacked section cannot be treated as zero-offset section, CMP stack + post stack migration imaging method doesn't work, then we must find another method that could image better, ellipse?evolving imaging method (PRO) is just a method that can be work when the subsurface strata have dipping reflectors.Based on the elliptic development theory, a new method for common shot gathers velocity analysis was proposed and the corresponding workflow was introduced in this paper. At first for selected velocity range, based on common shot gathers the elliptic development and coherent stacking were used to calculate zero-offset stacking section for every velocity, secondly by sorting the calculated zero-offset stacking sections, the common normal emergence point velocity spectrum were generated, according to the maximum energy criterion, the velocity for every common normal emergence point was determined, at last by utilizing the picked velocity, the true zero-offset stacking sections were acquired. In the velocity analysis method, the previously sorting of the velocity analysis gathers was not needed, and the common reflection point dispersion in routine velocity analysis was avoided. The results of model testing demonstrate the validity and accuracy of this method.