BVAS

Programs BVAS and BAMP 8.2.6 assume a viscoelastic medium. The results are inverted under a Kelvin-Voigt (KV) constituative model with program OCTAVE_CAINV3 8.2.7 Michaels (1998). Inversion under a Kelvin-Voigt-Maxwell-Biot (KVMB) model may be used to estimate hydraulic conductivity if porosity is available using OCTAVE_KD4kvmb program (Michaels, 2006). SH wave enhanced down-hole data in BSEGY format (*.seg files) are processed for body wave dispersion. The delf, frequency increment should be no smaller than the reciprocal of the record length. For a 0.5 second recording, 2 Hz is the finest resolution.

 bvas infile emin emax vmin vmax nvel fmin fmax delf bwd iskp ivscn
  
 infile  =input file name 
 emin    =minimum receiver elevation (float) 
 emax    =maximum receiver elevation (float) 
 vmin    =minimum velocity 
 vmax    =maximum velocity 
 nvel    =number of velocity increments
 fmin    =minimum frequency Hz
 fmax    =maximum frequency Hz 
 delf    =frequency increment Hz 
 bwd     =filter bandwidth Hz 
 iskp    =skip filtering (if files already exist)
           1=YES  0=NO (-1=NO and delete when done)
 ivscn   =output velocity scan data sets 
           1=YES  0=NO

The output includes a file, bvas.his which can be processed by the inversion code, cainv3 (section 8.2.7). The columns of the bvas.his file are also defined at the end of the *.lst file which contains details of the run. For example:

       Frequency     Phase Vel.     +/- m/s      Semblance       Tbar       Tvar

          10.00         275.70    17.588079         0.5065     0.0342     0.0083
          12.00         319.28    13.666108         0.5476     0.0144     0.0059
          14.00         458.14     9.981112         0.6169     0.0053     0.0019
          16.00         612.12     6.796203         0.8824     0.0016     0.0007
          18.00         554.49     6.774652         0.8730     0.0022     0.0008
          20.00         481.10     7.960438         0.8251     0.0028     0.0014
          22.00         466.08    11.081243         0.8044     0.0026     0.0021
          24.00         461.89    12.072690         0.7758     0.0018     0.0022
          26.00         454.63     4.133945         0.8045     0.0012     0.0007
          28.00         475.22     3.958418         0.8036     0.0011     0.0007

Other outputs include a Postscript plot, bvas.ps, a QC plot, bvasqc.ps and a number of semplance plots.

Figure 28: BVAS: SH body-wave dispersion and semblance results for down-hole data. These are the automated picks for maximum semblance as seen in Figure 29. Viscous, Kelvin-Voit behavior is an increase in velocity with frequency (Michaels, 1998).

Figure 29: BVAS: SH body-wave semblance results for down-hole data.