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Extracting More Information from Rig Source 3C-VSPs
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Fourth EAGE Borehole Geophysics Workshop, Nov 2017, Volume 2017, p.1 - 5
Abstract
Summary
Different VSP datasets studied by surface seismic geophysicists inspired three short notes, illustrating aspects seldom related by borehole seismic geophysicists:
- The first arrival times constitute the basic information from VSP’s, considered as the modern form of checkshots: therefore, the surface seismic processing operators would like to read the root mean square stacking velocity (Vrms) and the divergence factor (V2T), expressed versus vertical two way times (twt) in the VSP reports.
- Signal-to-Noise conditions in deep boreholes can be an issue in open hole sections: a critical case of noisy hole conditions during VSP acquisition has been analysed, concluding to the presence of infiltration microseismic noise near-linearly polarized into the preferred permeability azimuth in the plane radial to the borehole axis.
- Complex, interfered downgoing wavetrain obverved in borehole seismic indicates multipath seismic propagation in a heretogeneous medium. Time pick of “first arrival” is rendered approximate, at best, and signature deconvolution is often impossible, except in the case where the spatial distribution of the multipath wavetrain remains within a small solid angle, as verified from oriented 3C VSP records. In such case, a depth variant downgoing incident signature can be defined to properly compress the VSP data corridor stack domain.
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