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Abstract:
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In a fluid-saturated porous formation, an impinging seismic wave induces fluid motion. The motion of fluid relative to the rock frame generates an electric streaming current. This current produces electric and magnetic fields, which are called seismoelectric and seismomagnetic fields, respectively. When there is a fracture or a discontinuity, a radiating electromagnetic wave is also generated, in addition to local fields. Seismoelectric and seismomagnetic fields depend on the amplitude, frequency, and mode of the seismic wave, as well as the formation porosity, permeability, pore size, and fluid conductivity. In this paper, we describe laboratory results of seismoelectric and seismomagnetic fields induced by an acoustic source in borehole models. We use a piezoelectric source for acoustic waves and a point electrode and a high-sensitivity Hall-effect transducer for measuring the localized seismoelectric and seismomagnetic fields in fluid-saturated rocks. The dependence of seismoelectric conversions on porosity, permeability and fluid conductivity are investigated. Three components of the seismomagnetic field are measured by the Hall-effect transducer. At a horizontal fracture, the acoustic wave induces a radiating electromagnetic wave. |
