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G01V 3/30 (2006.01) E21B 47/01 (2006.01) G01V 3/28 (2006.01)
Patent
CA 1235179
-32- Abstract of the Disclosure An apparatus and method for measuring formation parameters by transmitting and receiving electromagnetic signals by antennas disposed in recesses in a tubular housing member and including apparatus for reducing the coupling of electrical noise into the system resulting from conducting elements located adjacent the recesses and housing. More particularly, a method and apparatus employing electrostatic, but not magnetic, shielding of the low impedance antenna systems and inductive signal coupling to enhance the signal at the receiver is disclosed. This system is capable of measuring formation parameters in the presence of con- ducting bodies, e.g., the drill string, permitting incorporation of the apparatus in a measuring while drilling (MWD) logging system. In a particular embodiment, high frequency electromagne- tic energy is used to measure formation resistivity. Small low impedance coils are arranged in the wall or around the outer circumferential surface of a steel drill collar and spaced from the surface a minimum distance to allow efficient propagation and reception. The low impedance receiver antennas are substantially electrostatically, but not magnetically, shielded and include inductive current coupling devices to further improve the signal. In a preferred embodiment, the coils are circularly configured about the collar and longitudinally spaced thereon to serve as transmitting and receiving elements which together with asso- ciated circuit components employ high frequency eletromagnetic wave propagation techniques to measure formation parameters. The received signals are phase shifted and amplitude attenuated as they pass through the formation, and formation parameters are determined by detecting variations in travel time and attenuation between longitudinally spaced receivers.
457020
Grayson William R.
Meador Richard A.
Thompson Larry W.
Halliburton Energy Services Inc.
Kirby Eades Gale Baker
Nl Industries Inc.
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