Introduction
Geotech’s latest implementation of its patented airborne AFMAG (Audio Frequency Magnetic) technology is the Z-TEM or Z-Axis Tipper Electromagnetic system. Z-TEM was introduced in mid-2007 and over 20, 000 line kms have been flown commercially for minerals exploration. In theory, as with some other electromagnetic techniques, it has applications for petroleum prospecting. From numerical modeling of various hydrocarbon plays, Z-TEM has a depth of investigation for resistive targets to several kilometers.
Z-TEM uses the natural or passive fields of the Earth as the source of transmitted energy. These natural fields are planar and due to the manner in which they propagate, are horizontal. Any vertical EM field is caused by conductivity contrasts in the Earth. The Z-TEM system measures the vertical EM field in the air along the survey lines and makes use of a base station to measure the horizontal fields. The assumption is that the horizontal fields are relatively homogenous over the survey area and the base station location. The vertical EM field is remotely referenced to the horizontal EM fields.