Shear-Wave Seismic and VSP with Virtual Sources

Shear-wave seismology holds great promise but always remains small niche activity due to a variety of operational and subsurface limitations. In this study we demonstrate that the Virtual Source method can overcome many of these limitations and revive shear-wave seismology. With an array of sources at the surface this method allows us to obtain a Virtual Shear Source at the location of each downhole geophone in a well. Firstly, in certain cases it allows us to generate pure shear-wave energy without P-wave contamination using conventional P-wave sources even in a marine environment. Secondly, we can construct SS images of the subsurface even through a complex near-surface for which the velocity model is unknown. Thirdly, we can control the polarization. All this is at a price of placing geophones in the subsurface and making downhole recordings. This price tag is expected to decrease with greater use of permanent downhole monitoring, cheap wells and instrumented oilfields.<br>We will show examples of SS images obtained through a complex near-surface and show shear-wave checkshots generated with the help of P-wave sources even in a marine environment. This<br>development may lead to a renaissance of shear-wave seismology especially for permanent seismic monitoring.