| Summary: | We present a new type of field measurement capable of detecting and characterizing
fractured (permeable) zones intersecting a borehole. The method is based on measuring
electrical fields generated by a borehole Stoneley wave. In this paper, we describe
the measurement technique, present field data, and propose a theoretical model, which
correctly predicts amplitudes and phases of the electrical fields measured in the borehole experiment.
The theoretical model and the field data demonstrate that the measurements of the
Stoneley-wave-induced electrical fields can yield information about the interconnected
porosity, and possibly about the permeability of the formation around the borehole.
We derive an estimate of the interconnected porosity from the field data, and show that it correlates well with the density of fractures intersecting the borehole. Our results
suggest that the borehole electroseismic method can be developed into a logging or a
VSP tool, with possible applications in reservoir characterization.
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