Patent ID: 8289808

Claim:
An apparatus for estimating Vp/Vs ratio of the rock formations remote from a borehole using a conveyed logging tool, the apparatus comprising: a first source arranged in the borehole and configured to generate elastic energy at a first frequency; a second source arranged in the borehole and configured to generate elastic energy at a second frequency, wherein the energy at the first frequency and at the second frequency intersect at a location away from the borehole; a sensor array configured to receive a third elastic wave, the third elastic wave being created by a non-linear mixing process from the elastic energy at the first frequency and the elastic energy at the second frequency in a non-linear mixing zone, the third elastic wave, having a frequency equal to a difference between the first and the second frequencies and a direction of propagation toward the borehole; and a processor arranged to identify a location of the mixing zone based on the arrangement of the first and the second sources, the direction of the third wave and selection rules governing non-collinear mixing in acoustically non-linear media, and to estimate Vp/Vs ratio based, in part, on the received third elastic wave and the arrangement of the first and second sources.