MODELING A SHOCK-WAVE SOURCE FOR SEISMIC WELL SURVEY

The shock wave seismic source has specific advantages for reservoir su rvey, particularly in the technique of vertical seismic profiling. Thi s paper is concerned with the modelling of the characteristics of a sh ock wave device under conditions typical of its use as a surface seism ic source. Such modelling necessitates numerical solution of the time- dependent conservation equations for axi-symmetric geometry under cond itions where the fluid in the surface borehole may be air or water. A version of the piecewise parabolic method has been used to take accoun t of the two-phase behaviour based on the formal properties of the wel l-known Tait equation of state for water. Results are presented which enable predictions to be made for use in the field of the pressure and velocity signatures of the shock wave source in terms of axial and ra dial profiles. Such information is significant in the assessment of th e degrees of compressional- and shear-wave energies delivered by the s ource in vertical seismic profiling surveys of reservoirs.