Separated Wavefields

Mitigating the Effect of the Receiver Ghost

Collocated groups of hydrophone pressure sensors and vertical velocity sensors record the continuous interference between the wavefield scattered upwards from the geology in the subsurface and the downgoing wavefield that carries the imprint of the reflecting sea surface, which is different for every shot. This downgoing wavefield is called the ghost wavefield.

Wavefield separation is a critical step in broadband seismic imaging workflows applied to multisensor streamer and node seismic data. The pressure and velocity sensors record each upgoing seismic event with equal polarity, while the time-delayed downgoing seismic event is measured with opposite polarity.

All events associated with sea-surface ghost reflections can be isolated and removed for traditional high-resolution imaging and subsurface characterization. Alternatively, separated data can be used for SWIM imaging to improve the resolution of the shallow subsurface where traditional imaging solutions fail.                              

The TGS wavefield separation solution preserves all pre-stack amplitude-versus-angle (AVA) information critical for accurate subsurface characterization by accounting for 3D emergence angle variations along each GeoStreamer.

Operationally, multisensor streamers are less noisy as they permit deep towing with a shallower front end to reduce tension and enable very wide streamer spreads. The upgoing wavefield has a rich low-frequency signal, courtesy of the deep towing, and also a rich high-frequency signal; this wavefield is not affected by sea-surface variations.

Accurately removing the time- and space-varying downgoing wavefield (the receiver ghost) improves survey repeatability for 4D reservoir monitoring and CCS/CCUS projects.