Borehole Model with Fractures

Seismoelectric ExplorationGeophysical Monograph Series(2021)

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In a homogenous porous material or in a continuous borehole, the conduction current exactly balances the streaming current induced by a seismic wave. The induced field is simply a stationary electric and magnetic field that moves along with the seismic wave. The apparent velocity of the stationary electric or magnetic signals is the same as the velocity of the seismic wave. If seismic waves traverse a discontinuity in electrical and/or mechanical properties, the imbalance in the currents induces an EM wave that can be measured remotely. Seismoelectric and seismomagnetic fields generated by seismic waves in fluid-saturated fractured borehole models are experimentally investigated with an electrode and a Hall-effect sensor. In a borehole with a horizontal fracture, the Stoneley waves induce seismoelectric and seismomagnetic fields on the borehole wall, and an electromagnetic (EM) wave propagating at light speed at the horizontal fracture. In a borehole with a vertical fracture, the acoustic field generated by an acoustic source is similar to that in a borehole without a vertical fracture. However, the acoustic wave propagating along the vertical fracture induces seismoelectric and seismomagnetic fields, whose apparent velocities are equal to that of a Stoneley wave. Experimental results show that two different kinds of electric and magnetic fields are generated by acoustic waves in boreholemodels with horizontal and/or vertical fractures. Seismoelectric and seismomagnetic well logging might be a new logging technique for exploring fractures in a borehole.
borehole model,fractures
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