Shear waves, seismic attenuation and a more robust well calibration using zero-offset VSP. Examples from conventional and unconventionals reservoirs in Argentina

Summary Borehole seismic is recorded by geophones or accelerometers placed on the borehole, then contain information about the reflection and transmission properties of the Earth, while surface seismic only include the recorded up going waves. Up going multiples in VSP do not outspread to the direct arrival curve. Consequently, corridor stacks can be described as a multiple free, zero phase, normal incidence response. Also, zero-offset P-wave VSP provides information about the seismic wave attenuation through Earth and shear components that may be generated by non-inelastic layers. Around 700 VSPs in Argentina were analysed, 15% of which have high potential to derive wave attenuation and shear data. The present study demonstrate the presence of shear waves in zero-offset P-wave VSP and proposes workflows to maximize the use of borehole seismic for a more robust seismic to well calibration to reduce uncertainties in seismic phase required for seismic interpretation, to estimate seismic wave attenuation and, extract shear components for processing and characterization projects. Shear waves from P-wave VSP can provide an actual low frequency Vs velocity model to 3D elastic inversion, and a Vp plus Vs model for microseismic surveys. Examples from conventional and unconventional reservoirs in Argentina are presented.