Borehole Seismic Techniques

Abstract

When seismic waves are recorded using geophone(s) in a well with the energy source at the surface, the survey is referred to as a well seismic survey and when the seismic waves are recorded using geophones in one well and the energy source in another nearby well, it is referred to as a cross-well survey. The well seismics include surveys known as check-shot and VSP and provide the all important measured true velocity, essential for time- to -depth conversion and seismic calibration. Cross well survey based on tomography, mostly used in monitoring EOR sweeps is very briefly touched.

Different types of VSP and their benefits are outlined with stress on seismic calibration through corridor stack. The difference between the check-shot and VSP surveys and distinction between VSP well (seismic) velocity and sonic velocity are pointed out. Shortcomings of check-shot and VSP velocity surveys and ways to check these are suggested.