CGG: Source Solutions
All seismic imaging begins with the release of acoustic energy into the water, continues with the propagation of this energy through the subsurface and finishes with the harvesting of encoded messages from the reservoir. To get the required response from the reservoir you have to start with the right sound, at the right level and from the right angle.
The image of the subsurface and the attributes of the reservoir have to be de-correlated from any imprint of the acquisition system. CGG has done extensive work to eliminate the echo of the water surface from the image and attributes. Our advanced deghosting technologies from acquisition to processing demonstrate the expected efficiency and accuracy on both the source and receiver sides of the Marine Acquisition System.
Full Source Characterization
However, our ambition is to improve the image resolution. The reality of acquisition reveals the marine source to be continuously moving. From a distance it appears as a single dot, quiet and static, but from close-up and shallow any element of the 250m2 source array structure can be distinguished. Removing the illumination imprint of this structure requires an accurate estimation of the seismic signature of each element at its real location.
Full Source Characterization technology enables the estimation of the source signature produced by each single element for any direction (azimuth) at any distance (offset) and for each single shot. A full acquisition system scrutinizes the sound propagation of each source element at near field, mid-field and far-field and dedicated real-time software performs joint inversion of those measurements. The complexity of the generated wavefield is revealed: the activated bubbles, their interactions, and their reflection from the sea surface. The contribution of each element at any location and any depth can be identified. Now the removal of the imprint of the marine source system from the images and attributes of the subsurface regardless of depth becomes possible:
3D source deghosting and designature, critical for shallow targets, accurately performs 3D receiver deghosting
3D deghosting and designature of BroadSource accurately releases the images and attributes from the bubble imprint on Low Frequencies
Monitoring of stability of the source signal for all azimuths and offsets enables the areas where shot to shot deconvolution is recommended to be highlighted
The expectations of 4D source repeatability are very high. Any source imprint, even on some azimuths or offsets, reduces the detectability threshold for the 4D signature. With Full Source Characterization technology, CGG moves forward, in combination with 4D illumination monitoring, to set the assessment of repeatability beyond the geometrical repeatability of source/receiver positions.