DATA-PROCESSING METHODS FOR CROSSWELL SEISMIC IMAGING

This paper discusses a procedure to process crosswell seismic data, ac quired from many source and receiver locations, into a stacked section . It includes a number of steps such as wavefield separation, common r eflection point (CRP) gathering, velocity analysis, moveout correction , and stacking. This procedure is tested with synthetic acoustic-wave data generated from tracing rays in a simple geology model. Crosswell data consisting of complex wavefields are sorted into various gathers (common source, common receiver, common interval, and common mid-depth ) for noise removal and wavefield separation. Common interval gathers are useful in separating direct arrivals from reflections because of a high-angle relationship between them. Common source gathers are used to separate upgoing and downgoing reflected events. The separated refl ections are sorted into CRP gathers, assuming flat layers and a consta nt velocity medium. The hyperbolic reflected events in CRP gathers are corrected for moveout using a time-distance relation that describes t he horizontal and vertical components of normal moveout. A zero-interv al gather is used to derive velocity for the moveout corrections. The resultant stacked section shows a wide lateral coverage of the layers, especially at the zone of interest.