Borehole apparatus and methods for measuring formation velocities as a

Abstract

Borehole tools are provided with at least one transmitter which generates acoustic waves at a plurality of azimuthal locations about the borehole, and at least one receiver which receives and measures a characteristic (e.g., velocity) of the acoustic waves at related azimuthal locations. The direction of minimum velocity around the borehole is considered the direction of maximum uniaxial stress in the formation. From the velocity as a function of azimuth information, determinations of formation properties, and logs of the same can be made. The azimuthal direction of minimum velocity around the borehole predicts the propagation direction of artifically induced hydrofractures. The velocity variation around the borehole at a particular depth of the borehole is taken as an indication of susceptibility to failure, with higher velocity variations indicative of a more poorly consolidated formation or a formation with a large uniaxial stress. The curvature of the velocity versus stress curve in the formation is also indicated by how poorly a sine wave fits to the velocity data. Other parameters of the formation are obtained by fitting a best fit curve to the azimuth versus velocity data, where adjustable parameters of the best fit curve constitute the formation parameters.