Crosswell Seismic Processing: Automatic Velocity Analysis, Filtering, and Reflection Imaging
A study on crosswell seismic data processing is presented. Three surveys from Texas and Alberta, using downhole airgun or explosive charges and geophone or hydrophone streamers, are analyzed. Strong tube waves generally obscure useful but weak reflections. To suppress them, f-k, median and alpha-trimmed mean filters are used. The median filter works best. A new velocity analysis technique is developed, assuming velocity increasing linearly with depth, to automatically derive a one-dimensional velocity profile from first-arrival traveltimes. Tests show encouraging results. Different methods of extracting reflection information from crosswell data are discussed. An imaging technique using common-reflection-point stacking is developed and tested with a synthetic and field data. This technique enables one to take advantage of the high-fold subsurface coverage of crosswell reflections and process crosswell data like surface seismic CDP data. The stacked reflection images constructed show high resolution that is difficult to obtain from surface seismic or VSP data.