Simulation of well-log response of the acoustically-induced electromagnetic field in a porous formation

During acousto-electric logging, the acoustic waveexcited by a point acoustic source in a fluid-filled borehole propagatesinto the fluid-saturated porous medium and causes relative motion betweenthe charge-bearing pore fluid and the skeleton, inducing electromagneticfield. To simulate the logging response, a numerical full-waveformsimulation method is proposed. The acoustic field is taken as uninfluencedby the converted electromagnetic field, and is solved separately. Theelectric field is taken as quasi-steady. The full Biot-Rosenbaum model isadopted to obtain expressions for the acoustic field around the borehole.These expressions are then used to formulate the converted electric andmagnetic fields in and out of the borehole. Calculations show there areelectric and magnetic fields that accompany the compressional, the shear andthe Stoneley waves. And there is a critically refracted electromagneticwave, which travels along the borehole wall. The amplitude of this wave isvery weak in the full waveform. Both the axial and the radial components ofthe electric field increase when the receiver is placed farther off theborehole axis. On the borehole wall, the shape of the waveform of magneticfield is similar to that of the axial electric field.