Use of Electrodes and Multi-Frequency Focusing to Correct Eccentricity and Misalignment Effects on Transversal Induction Measurements

Abstract

A multicomponent induction logging tool uses a nonconducting mandrel. A central conducting member including wires that electrically connect at least one of the antennas to another of the antennas. Electrodes disposed about the transmitter antenna form a conductive path through a borehole fluid to the central conducting member.

1 . An apparatus for determining a resistivity property of an earth formation, the apparatus comprising:
 (a) a logging tool having a non-conductive mandrel;   (b) a transmitter antenna;   (c) a pair of receiver antennas;   (d) a central conducting member including wires that electrically connect at least one of the antennas to another of the antennas; and   (e) a pair of electrodes disposed about the transmitter antenna forming a conductive path through a borehole fluid to the central conducting member.   
   
   
       2 . The apparatus of  claim 1 , wherein the transmitter antenna further comprises an antenna with an axis inclined at a nonzero angle to an axis of the logging tool. 
   
   
       3 . The apparatus of  claim 1 , wherein one of the pair of receiver antennas further comprises a bucking antenna. 
   
   
       4 . The apparatus of  claim 1 , wherein the receiver antennas further comprise antennas with axes inclined at a nonzero angle to an axis of the logging tool. 
   
   
       5 . The apparatus of  claim 1  further comprising a conveyance device configured to convey the logging tool into a borehole in the earth formation, the conveyance device selected from (i) a wireline, and (ii) a drilling tubular. 
   
   
       6 . The apparatus of  claim 1  further comprising a processor configured to:
 (i) activate the transmitter antenna at a plurality of frequencies;   (ii) perform a multifrequency focusing (MFF) of signals received by the receiver antennas; and   (iii) determine the resistivity property of the earth formation from the results of the MFF.   
   
   
       7 . A method of determining a resistivity property of an earth formation, the method comprising:
 (a) conveying a logging tool having a non-conductive mandrel, a transmitter antenna, a pair of receiver antennas and a central conducting member including wires that connect at least one of the antennas to another of the antennas, into a borehole;   (b) positioning a pair of electrodes about the transmitter antenna and forming a conductive path through a borehole fluid to the central conducting member;   (c) activating the transmitter antenna;   (d) producing signals in the pair of receiver antennas responsive to the activation of the transmitter antenna; and   (e) determining the property of the earth formation from the produced signals.   
   
   
       8 . The method of  claim 7  further comprising, using for the transmitter antenna, an antenna with an axis inclined at a nonzero angle to an axis of the logging tool. 
   
   
       9 . The method of  claim 7  further comprising using one of the pair of receiver antennas as a bucking antenna. 
   
   
       10 . The method of  claim 7 , further comprising using, as the receiver antennas, antennas with axes inclined at a nonzero angle to an axis of the logging tool. 
   
   
       11 . The method of  claim 7  further comprising conveying the logging tool into a borehole in the earth formation using a conveyance device selected from (i) a wireline, and (ii) a drilling tubular. 
   
   
       12 . The method of  claim 7  wherein determining the property further comprises:
 (i) operating the transmitter antenna at a plurality of frequencies;   (ii) performing a multifrequency focusing (MFF) of signals received by the receiver antennas; and   (iii) determining the resistivity property of the earth formation from the results of the MFF.   
   
   
       13 . The method of  claim 7  wherein the property is selected from (i) a vertical resistivity, (ii) a horizontal resistivity, (iii) a sand fraction, (iv) a water saturation, (v) a formation dip, and (vi) an azimuth. 
   
   
       14 . A computer readable medium for use with an apparatus for determining a property of an earth formation, the apparatus comprising:
 (a) a logging tool having a non-conductive mandrel;   (b) a transmitter antenna;   (c) a pair of receiver antennas;   (d) a central conducting member including wires that electrically connect at least one of the antennas to another of the antennas; and   (e) a pair of electrodes disposed about the transmitter antenna forming a conductive path through a borehole fluid to the central conducting member;   the medium comprising instructions that enable a processor to determine from signals received by the pair of receiver antennas resulting from activation of the transmitter antenna the property of the earth formation.   
   
   
       16 . The medium of claim  15  further comprising at least one of (i) a ROM, (ii) an EPROM, (iii) an EEPROM, (iv) a flash memory, and (v) an optical disk.