A 3D seismic survey was conducted in Ogata area, one of Japanese mature oil fields. The survey was aimed to obtain a basic data set, which is useful for studying the effects of irregular data acquisition geometry, and to provide the precise information on the subsurface structure for finding additional reserves. The survey area was previously the second largest lake in Japan and has been changed to rice fields after reclamation. Few difficulties in seismic data acquisition were expected and dense regular data acquisition geometry was planned to use in the survey. However, acquisition work encountered many hazards because a lot of unexpected constraints came from the reclaimed land. Moreover, obtained shot records showed the very complex nature of seismic wave fields. Especially, strong ringing waves masked weak reflection signals. Spatial variation of these ringing waves was investigated and the origin was modeled as critical refraction of multiple reflected waves within a very thin surface layer. Those results can provide valuable knowledge for seismic survey in areas with similar surface conditions. In seismic data processing, these ringing waves were successfully suppressed at the earlier data processing stage by FK filter in common shot and receiver domains followed by deconvolution. After this suppression, remaining data processing became more effective and gave a precise depth image. Various analyses to the obtained processing vintage such as coherency cube and attributes revealed the existence of minor faults precisely, which were not recognized previously. These could give a new interpretation of the area. As a result, the data set can be very useful for the evaluation of irregular data acquisition geometry as well as the exploration in the area.

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