Virtual source method applied to Mars field OBC data for time-lapse monitoring

Main Content:
         The virtual source method has recently been proposed to image and monitor
below a complex and time-varying overburden. The method requires surface
shooting recorded by subsurface receivers placed below the distorting or chang-
ing part of the overburden. Redatuming the recorded response to the receiver
locations allows the reconstruction of a complete downhole survey as if the
sources were also buried at the receiver locations. 
       The ability to redatum thedata independent of the knowledge of time-varying overburden velocities makes the virtual source method a valuable tool for time-lapse monitoring. We apply
the virtual source method to the Mars field OBC data acquired in the deepwa-
ter Gulf of Mexico with 120 multi-component sensors permanently placed on
the seafloor. 
         Applying to the virtual source method, a combination of up-down
wavefield separation and deconvolution of the correlation gather by the source
power spectrum suppresses the influences of changes in the overburden (sea wa-
ter), thus strengthening the virtual source method for time-lapse monitoring.