Near Surface Geophysics > VSP with a hydrophone at well M3

The video shows the processing sequence applied to VSP data recorded with a hydrophone.

The VSP shows down going P waves and a low level of Stoneley modes. A wave number filter which preserves the positive wavenumbers has been applied to extract the down going waves and to facilitate the time picking of the first arrivals. The picked times are used to realize the flattening and then the extraction of the down going P- waves with a narrow band wave number filter. The difference between the down going waves and the down going P- waves is the down going Stoneley waves. The residue, difference between the initial VSP data and the down going waves, is computed. It mainly shows up going Stoneley waves and noise. A narrow band wave number filter applied after velocity correction is used to extract the up going Stoneley waves. The velocity is negative, its absolute value is of the order of 1300 meters per second. The stack of the down going waves and the up going Stoneley waves has been subtracted to the initial VSP data to obtain a second residue. The residue is mainly noise.

We can notice that the up going Stoneley modes are converted waves. They are generated by the down going P-waves. A deconvolution of the up going Stoneley modes by the down going P-waves allows to locate accurately the depths, where the conversions occur.