System and method for investigating sub-surface features of a rock formation

摘要

H:/kxg/Interwoven/NRPortbl/DCC/KXG/6601965_1.DOC - 13/08/14 A method and system for investigating rock formations outside a borehole are provided. The method includes generating a first acoustic wave at a first frequency by a first acoustic source; and generating a second acoustic wave at a second frequency by a second acoustic source. The first and the second acoustic sources are arranged within a localized area of the borehole. The first and the second acoustic waves intersect in an intersection volume outside the borehole. The method further includes receiving a third acoustic wave at a third frequency, the third shear acoustic wave returning to the borehole due to a non-linear mixing process in a non-linear mixing zone within the intersection volume at a receiver arranged in the borehole. The third frequency is equal to a difference between the first frequency and the second frequency. si 0 0 0 itt... 4JWJ%. An '4 'I.// tvall 21 4 V 0 h c x it - I L'4 0 1 oal' I M