Calibration of xx, yy and zz induction tool measurements

Abstract

Measurements made with a multicomponent logging system oriented in a horizontal position above the surface of the earth must satisfy certain relationships. These relationships are used to establish calibration errors in the system.

1 . A method of using a system having at least one transmitter and a plurality of receivers for making multicomponent induction measurements, the method comprising: 
 (a) positioning the system above the surface of the earth;    (b) orienting the system so that an axis of the at least one transmitter is substantially parallel to the surface and substantially collinear with an axis of at least one of the plurality of receivers;    (c) obtaining multicomponent measurements at at least one frequency and at least one rotational angle of the system; and    (d) determining from the multicomponent measurements an indication of a calibration error in at least one of the multicomponent measurements.    
   
   
       2 . The method of  claim 1  wherein: 
 (i) the system is adapted for use in a wellbore in the earth formation; and    (ii) the at least one transmitter comprises three transmitters orthogonal to each other.    
   
   
       3 . The method of  claim 2  wherein the three transmitters are not at substantially the same position (non co-located).  
   
   
       4 . The method of  claim 1  wherein the system is adapted for aerial use.  
   
   
       5 . The method of  claim 2  wherein the multicomponent measurements comprise xx, yy, and zz measurements, and wherein determining the indication of the calibration error comprises using a relation of the form:  
     
       

       H 
       xx 
       =H 
       yy 
       +H 
       xx  

     
     where H xx , H yy  and H zz  are magnetic field measurements in the xx, yy, and zz directions.  
   
   
       6 . The method of  claim 3  wherein: 
 (i) the multicomponent measurements comprise xy, and zz measurements;    (ii) the at least one rotation angle comprises an angle φ; and    (iii) determining the indication of the calibration error comprises using a relation of the form:      σ xy =σ zz  sin 2φ    where the σ's are apparent conductivity values at the angle φ.    
   
   
       7 . The method of  claim 5  wherein the at least one rotation angle comprises angles of 0° and 90°;  
   
   
       8 . A system for making multicomponent induction measurements, the system comprising: 
 (a) at least one transmitter and a plurality of receivers that make multicomponent measurements at at least one frequency and at least one rotational angle;    (b) a processor which determines from the multicomponent measurements made at a substantially horizontal configuration of the system an indication of a calibration error in at least one of the multicomponent measurements.    
   
   
       9 . The system of  claim 8  wherein the at least one transmitter comprises three transmitters orthogonal to each other, the three transmitters disposed on a logging tool conveyed into a borehole in the earth formation.  
   
   
       10 . The system of  claim 9  wherein the three transmitters are not at substantially the same position (non co-located).  
   
   
       11 . The system of  claim 8  further comprising one of (i) a fixed wing aircraft, and, (ii) a helicopter, which maintains the at least one transmitter and the plurality of receivers in the substantially horizontal configuration.  
   
   
       12 . The system of  claim 9  wherein the multicomponent measurements comprise xx, yy, and zz measurements, and wherein the processor determines the indication of the calibration error comprises using a relation of the form:  
     
       

       H 
       xx 
       =H 
       yy 
       +H 
       zz  

     
     where H xx , H yy  and H zz  are magnetic field measurements in the xx, yy, and zz directions.  
   
   
       13 . The system of  claim 10  wherein: 
 (i) the multicomponent measurements comprise xy, and zz measurements;    (ii) the at least one rotation angle comprises an angle φ; and    (iii) the processor determines the indication of the calibration error comprises using a relation of the form:      σ xy =σ zz  sin 2φ    where the σ's are apparent conductivity values at the angle φ.    
   
   
       14 . The system of  claim 12  wherein the at least one rotation angle comprises angles of 0° and 90°;  
   
   
       15 . The system of  claim 9  wherein the processor is at one of (i) a downhole location, (ii) a surface location, and, (iii) a remote location.  
   
   
       16 . A machine readable medium for use with a system having at least one transmitter and a plurality of receivers for making multicomponent induction measurements, the medium comprising instructions for: 
 (a) positioning the system above the surface of the earth;    (b) orienting the system so that an axis of the at least one transmitter is substantially parallel to the surface and substantially collinear with an axis of at least one of the plurality of receivers;    (c) obtaining multicomponent measurements at at least one frequency and at least one rotational angle of the system; and    (d) determining from the multicomponent measurements an indication of a calibration error in at least one of the multicomponent measurements.    
   
   
       17 . The medium of  claim 16  wherein: 
 (i) the system is adapted for use in a wellbore in the earth formation; and    (ii) the at least one transmitter comprises three transmitters orthogonal to each other.    
   
   
       18 . The medium of  claim 17  wherein the three transmitters are not at substantially the same position (non co-located).  
   
   
       19 . The medium of  claim 16  wherein the system is adapted for aerial use.  
   
   
       20 . The medium of  claim 17  wherein the multicomponent measurements comprise xx, yy, and zz measurements, and wherein the instructions further comprise a relation of the form:  
     
       

       H 
       xx 
       =H 
       yy 
       +H 
       zz  

     
     where H xx , H yy , and H zz  are magnetic field measurements in the xx, yy, and zz directions.  
   
   
       21 . The medium of  claim 18  wherein: 
 (i) the multicomponent measurements comprise xy, and zz measurements;    (ii) the at least one rotation angle comprises an angle φ; and    wherein the instructions further comprise a relation of the form:      σ xy =σ zz  sin 2φ    where the σ's are apparent conductivity values at the angle φ.    
   
   
       22 . The medium of  claim 16  wherein the medium is selected from the group consisting of (i) a ROM, (ii) an EPROM, (iii) an EAROM, (iv) a Flash Memory, and, (v) an optical disk.