Experimental ultrasonic microseismograms using scaled realistic earth and borehole models

This experimental study is aimed at simulating and interpreting borehole sonic logs in a laboratory environment. Our interest is focused on pattern recognition of seismic signatures associated with formation inhomogeneity and irregular boreholes, typical as those encountered in a single borehole environment. A comprehensive set of high-resolution full waveform ultrasonic responses in scaled realistic earth and borehole models was acquired. The borehole models presented in this paper target the effect of these two factors on the microseismogram: i) a high velocity layer between lower velocity materials; and ii) a washout in a homogeneous medium.
We first describe the specimens, experimental apparatus, and data acquisition and processing system of the experiment; and then present the different patterns of microseismograms that we have obtained. Finally we analyze the results and provide some guidance as how these images can be used in a practical application. The results suggest that understanding of the signal due to the interaction between the layered medium and the borehole can assist in the interpretation of microseismograms acquired in the field and the associated Q logs.