Source and receiver responses in boreholes

Abstract

This report considers the acoustic interaction between the acoustic freld rn a borehole and the elastic field in the surrounding formation. The problem with acoustic-seismic radration of energy from a source in a fluid filled borehole with a drrllstring surrounded by an elastic formation of infrnrte extent is first consrdered. The exact solution is established and simplified expressions are derived for the low frequency case. The source produces a compressional field and a shear wave field. The compressional field has a maximum value at the direction perpendicular to the axis of the borehole, the shear field will in most cases has a maximum approxtmately at an angle of 45". However, in special cases the radiation out into the formation may be completely dominated by shear radiation in a very narrow angle. Secondly, the response of a sensor in the borehole due to an incoming plane wave is considered and the complete solution valid for all frequencres is determined. Numerical examples shows that the receiving response can be very complicated and composed of several modes and each of them may have strong resonances.