Patent ID: 6891777

Claim:
A method for evaluating a borehole traversing a subsurface formation, comprising: transmitting an acoustic signal into the borehole at each of a plurality of azimuthal positions; determining a transit time for a front face echo signal for the plurality of acoustic signals; determining a transit time for a formation echo signal for each of the plurality of acoustic signals; selecting a threshold curve for each of the plurality of acoustic signals based on an amplitude of the front face echo signal, a power output of a transducer, a tool geometry, and an offset of said tool; determining the formation echo signal for each of the plurality of acoustic signals as a signal with an amplitude that exceeds the threshold curve; measuring an elapsed time between the transmission of the acoustic signal and a recording of the formation echo signal for each of the plurality of acoustic signals; determining a distribution of formation echo signal transit times in each of a plurality of azimuthal sectors; determining a farther standoff for each of the plurality of azimuthal sectors as the standoff distance corresponding to a farther-mode transit time by using a speed of the acoustic signal in a borehole fluid; determining a closer standoff for each of the plurality of azimuthal sectors as a standoff distance corresponding to a closer-mode transit time by using the speed on the acoustic signal in the borehole fluid; and in each of the plurality of sectors, determining if either or both of the farther standoff and the closer standoff is a preferential position of said tool.