Multicomponent Seismic by Adun Gamaliel

 

For some time, seismic data acquisition was carried out as a single component survey. The vector-based thinking of seismic technology was the starting point for the multicomponent approach to seismic acquisition. Multicomponent seismic technology is one in which several wavefield components are measured and integrated to enable better understanding of subsurface geology.

Two major waveforms propagate through the subsurface; P and S waves. In reality, the S-waves do not propagate the same way in all directions through the subsurface. They distort the earth differently and travel at different speeds. Hence, revealing different physical properties of the earth.

In conventional seismic acquisition, only the P or compressional wave mode is recorded. Therefore, the sources/receivers used are those which propagate/measure only the P-wavefield component. In multicomponent seismic acquisition, an array of sources and receivers each propagating/sensing different wavefield components are used. The multicomponent seismic therefore carries information for the propagation of both P (compressional) and S (shear) wavefield components through the subsurface.

P-waves are sensitive to both geology (rock units) and the fluid contained in them whereas S-waves are sensitive to geology only (rock units). As a result of this disparity, both wavefields can be combined such that geologic information in fluid-filled sedimentary units can be better resolved. With multicomponent seismic technology, this can be done with a higher degree of accuracy compared to conventional seismic because both wavefields are recorded whereas in Conventional seismic only the P-wavefield is recorded. Consequently, the multicomponent seismic is a better tool for reservoir characterization.

Multicomponent seismic processing is very similar to the conventional seismic processing only that the vectorial peculiarity of multicomponent seismic coupled with the various mode conversions, must be carefully treated and accounted for. Special processing steps in multicomponent seismic processing include; geometry and clock synchronization, wavefield separation, data rotation, common-conversion point (CCP) processing, asymptotic binning, polarity corrections and reversals, up-down deconvolution, directional designature, etc.

The images produced by multicomponent seismic technology have several advantages over their conventional seismic counterparts. These include improved signal to noise ratio, imaging intra-reservoir features, improved imaging and resolution, 4D reservoir monitoring, lithology discrimination, fracture and stress identification and characterization, fluid identification, deployment in congested areas, etc.

The multicomponent seismic endeavor is more capital and labor intensive than its conventional P-P counterpart. However, the information gains and lowered risks afforded by the multicomponent approach are well worth the investment as the overall chance of success is improved as the uncertainties are reduced.

References

Bob A. Hardage, M. V. DeAngelo, P. E. Murray, D. Sava, 2011, Multicomponent seismic technology, Geophysical references series; no. 18, 1-123.

Multicomponent; Compressional, Shear and Converted Wave Seismic, CGG Veritas.



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