Numerical modeling of the electromagnetic coupling effects for phase error correction in EIT borehole measurement

Electrical Impedance Tomography (EIT) applications in geophysics require long electrode chains (25 m) for current injection and potential measurements. Undesired inductive coupling between the wire loops for current injection and potential measurement and capacitive coupling between the cable shield and the soil strongly decrease the phase accuracy of such measurements for frequencies above 100 Hz. Therefore, the bandwidth of EIT field measurements is typically limited to the mHz to Hz range. To overcome this limitation, we derived correction procedures for inductive and capacitive coupling by combining numerical modeling with calibration measurements. The correction procedures were verified with test measurements, where a phase accuracy better than 1 mrad at 10 kHz was achieved.