Crosshole seismoelectric measurements in borehole models with fractures

Abstract

Laboratory experiments are performed in crossborehole models with fractures to investigate seismoelectric conversions in the fractures. Using an electrode in a borehole, we measure the electric field induced by an acoustic wave, and we investigate the relationship between the electric signal and the fracture aperture using ultrasonic fracture borehole models. The experimental results confirm that a radiating electromagnetic (EM) wave is induced by a guide wave at a fracture between an acoustic source and electric receiver boreholes. The position of a vertical or inclined fracture between two boreholes can be determined using the arrival times of the EM wave and the formation velocity by placing the acoustic source at a different depth and recording electric signals with real or synthetic arrays of acoustic and electric receivers in the second borehole. Crosshole seismoelectric measurements might be a technique for investigating fractures between boreholes more directly than traditional acoustic measurements.