APPARATUS FOR MICROINDUCTIVE INVESTIGATION OF EARTH FORMATIONS

摘要

A wall-engaging apparatus for microinductively investigating a characteristic of an earth formation traversed by a borehole includes an antenna set mounted in a longitudinally elongated body adapted for a sliding engagement withthe wall of said borehole. The antenna set includes a first antenna element andidentical second and third antenna elements located in electromagnetic symmetry about the first antenna element. Means are included for differentially coupling said second and third antenna elements. Either the first antenna element or the differentially-coupled second and third antenna elements may be energized by suit-able means, while the other is coupled to means for receiving signals indicative of said characteristic. In another wall-engaging apparatus for microinductively investi-gating a characteristic of earth formations traversed by a borhole, a transmitter antenna is mounted in a conductive wall-engaging body, within a volume bounded in part by an integral conductive backplane and conductive sidewall and opening to the wall-engaging face of the body, for coupling focussed electromagnetic energyinto a formation engaged by the wall-engaging face of the body. The volume preferably is conformal with the transmitter antenna. Means are included for ener-gizing the transmitter antenna and for detecting a magnetic field from the engaged formation arising from the coupled electromagnetic energy.