Reflection imaging for synthetic crosswell seismic data

Guoping Li, Robert R. Stewart

A complete processing procedure for crosswell reflection imaging is presented in this paper. The final result produced from this procedure is a depth stacked section. Before the stacked section can be generated, a number of intermediate steps need to be applied. After preprocessing, crosswell seismic data of multi-fold coverage are processed in common interval gathers to remove direct arrivals. In common interval gathers, reflected waves have sharp angles against the direct arrivals. This characteristic is useful when applying velocity filters to eliminate the direct arrivals. The data are then sorted into common source gathers, where upgoing and downgoing reflections have opposite dipping angles and therefore can be separated through f-k filtering. The crosswell reflection imaging is achieved by using the Common Reflection Point Stacking Method, whose theory is given in this paper. The common reflection point stacking method consists of sorting data into common reflection point gathers, applying horizontal and vertical moveout corrections, and stacking the CRP gathers. Velocity information is needed for these moveout corrections. To derive the velocity, a technique of velocity scanning is used in a zero interval gather. The CRP stacking method assumes a constant velocity medium and flat reflectors. The stacked wavefields for upgoing and downgoing reflections are combined, followed by a time-depth conversion. The processing procedure discussed in this paper is believed to provide an effective and simple way to handle a large crosswell seismic data set. To show this, synthetic crosswell reflection data consisting of 55 shots and 101 receivers were generated and processed following the procedure presented here. A study on real crosswell reflection seismic data imaging is given in a separate paper by Li and Stewart (1993).