BroadSeis

CGG's BroadSeis™ solution delivers the most detailed high-resolution subsurface images with the best low frequencies from a combination of advanced equipment, proprietary variable-depth streamer profiles and deghosting and imaging technology.

Gulf of Mexico BroadSeis example

Comparison from the Gulf of Mexico. BroadSeis achieves an impressive 2.5 - 155 Hz of signal - almost 6 octaves, providing exceptional resolution and penetration.

As a consequence of the unique, streamer configuration, BroadSeis is able to deliver the deepest tow in the industry, up to 50 m. Combining this with the exceptional low-noise characteristics of Sentinel solid streamers delivers the lowest frequencies with the best signal to noise ratio available.

Benefits:

BroadSeis delivers the clearest images and details at the reservoir from exceptionally sharp and clean wavelets without sidelobes, from over 6 octaves of bandwidth, to provide:

  • better penetration through complex overburdens with improved signal-to-noise ratios for deeper targets delivered by the ultra-low frequencies
  • more reliable AVO from ghost-free wavelets more quantitative seismic inversion, as the low frequencies mean that there is no necessity for a well-derived low frequency model
  • better resolution of important features such as thin beds and stratigraphic traps from sharper wavelets without side-lobes.
  • enhanced layer differentiation, with improved texture and character, making interpretation more straightforward due to the broad bandwidth
  • high resolution shallow images for site surveys and drilling risk assessment 
  • extended weather window for greater operational efficiency and faster turnaround times due to deep tow reducing weather-related noise.
How BroadSeis works

How it works

Towed streamer data are affected by a receiver ghost, caused by the reflection of data back down from the sea surface. The up-going primary energy and the down-going ghost energy interfere, causing a notch in the amplitude spectrum where these are out of phase and a boost where they are in phase. The frequency of the ghost notch depends on the depth of the receivers.

BroadSeis acquires both low and high frequencies by using a variable-depth towing configuration. With this configuration, the receiver ghost notch varies along the cable and this “notch diversity” is exploited by the proprietary deghosting technique. The variability of the streamer depth and shape of the cable can be tuned for different targets so that the notch diversity and output spectra are optimized for each survey.

Thus conventional flat streamer data are "tuned" to a specific frequency range whereas BroadSeis variable-depth streamer data are "detuned", since the ghost notches are at different frequencies for different offsets within any common midpoint and therefore cancel on stacking.

Deghosting

CGG has developed an extensive toolbox of deghosting algorithms that can be applied to data prior to imaging. Our Ghost Wavefield Elimination (GWE) technique uses linear Radon equations which have been modified to include re-datum and re-ghost terms, resulting in a surface datum Tau-p model. This model enables separation of the upgoing and downgoing waves and is used for receiver deghosting and to re-datum data. The method assumes 2D wavefield propagation along the streamers and is suitable for most 2D and 3D data acquired using a narrow- or wide-azimuth streamer geometry.

BroadSeis deghosting

Common shot displays showing input , up-going and down-going components, with common channel displays before and after deghosting with associated amplitude spectra in dB (input in blue, deghosted in red)

For broadband processing of full-azimuth data (such as those acquired by StagSeis™) or reflections that exhibit strong 3D effects, use of our full 3D deghosting technique is required. This uses a progressive sparse Tau-Px-Py inversion to perform 3D joint deghosting and crossline interpolation in one step, thereby overcoming the issue of coarse and irregular crossline sampling.

BroadSeis is operationally robust and fully compatible with streamer steering, wide-azimuth geometries and 4D monitoring. When combined with BroadSource to eliminate the source ghost notch, the high frequencies are limited only by the sampling interval Nyquist and the absorption of the earth, without compromising the excellent low frequencies.