Seismoelectric and seismomagnetic measurements in fractured borehole models

Abstract

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 and flexural waves induce seismoelectric and seismomagnetic fields on the borehole wall and an electromagnetic wave propagating at light speed at the horizontal fracture. In a borehole with a vertical fracture, the acoustic field generated by a monopole or dipole 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 borehole models with horizontal and/or vertical fractures. One is an electromagnetic wave propagating with light speed. The second is a stationary or localized seismoelectric and seismomagnetic field. Seismoelectric and seismomagnetic measurements might be a new logging technique for exploring fractures in a borehole.