Patent ID: 7649804

Claim:
A method for determining an in-situ rock yield stress state of a geological formation surrounding a borehole, comprising: providing a borehole logging tool configured to be placed within the borehole, the borehole logging tool being configured to excite a sonic response within the borehole and to record a plurality of waveforms indicative of the sonic response; providing a processor, the processor containing instructions which when executed cause the processor to receive the plurality of recorded waveforms and to analytically: a. determine within at least one axial plane containing a borehole axis a radial profile for each of an axial effective stress, a radial effective stress, and a hoop effective stress; b. calculate from the effective stresses within the at least one axial plane a predicted radial shear response radial profile; c. determine from the plurality of recorded waveforms, a waveform-based estimate of a shear response radial profile within the at least one axial plane; d. identify within the at least one axial plane, a maximum radial distance at which a difference between the predicted shear response radial profile and the waveform-based estimated shear response radial profile is greater than a difference threshold; and e. determine at the identified maximum radial distance, the respective axial, radial, and hoop stresses, the identified stresses being indicative of an in-situ yield stress state of the rock.