Issue: 11
, Volume: 55
, Уear of publication: 2014
Serial edition: Russian Geology and Geophysics
Pages: 1333-1339
Abstract
The effect the metal casing of a vertical borehole may exert on transient electromagnetic (TEM) responses has been studied in a field experiment. Eddy currents in the casing affect transients only slightly at early times, but the casing effect predominates at late times. Therefore, early-time TEM response measured near a borehole can provide information on shallow subsurface. The late-time TEM signals induced by the eddy currents in the casing show exponential behavior b ъexp(- t /t). The time constant t refers to the rate of eddy current decay in the casing; the amplitude b
