Electrical power supply arrangement for a downhole measurement assembly

Abstract

A downhole measurement assembly comprising a metal casing housing a plurality of tool sections, one of which includes a detector sensitive to a magnetic field, and a DC power supply for said tool sections, the power supply and the tool sections being electrically connected to the casing, characterised in that the power supply is connected to at least one tool section via a switching circuit and a conductor arrangement, the switching circuit comprising a capacitor, a plurality of switches and control means operative alternately to charge the capacitor from the DC supply and discharge the capacitor through said at least one tool section using the conductor arrangement so as to inhibit the generation of an electromagnetic field in the conductor arrangement between the capacitor and the said at least one tool.

1 . A downhole measurement assembly comprising a metal casing housing a plurality of tool sections, one of which includes a detector sensitive to a magnetic field, and a DC power supply for said tool sections, the power supply and the tool sections being electrically connected to the casing, characterised in that the power supply is connected to at least one tool section via a switching circuit and a conductor arrangement, the switching circuit comprising a capacitor, a plurality of switches and control means operative alternately to charge the capacitor from the DC supply and discharge the capacitor through said at least one tool section using the conductor arrangement so as to inhibit the generation of an electromagnetic field in the conductor arrangement between the capacitor and the said at least one tool.  
   
   
       2 . An assembly according to  claim 1  wherein the switching circuit includes a plurality of electrically controlled switches.  
   
   
       3 . An assembly according to  claim 2  wherein the electrically controlled switches are MOSFETs.  
   
   
       4 . An assembly according to  claim 1  wherein the control circuit is an oscillator.  
   
   
       5 . An assembly according to  claim 4  wherein a switch is provided for switching off the oscillator.  
   
   
       6 . An assembly according to  claim 4  wherein the oscillator operates in the range of 50-65 KHz.  
   
   
       7 . An assembly according to  claim 1  wherein there are two capacitors connected to the power supply by switches such that as one capacitor is connected to the power supply so as to be charged, the other capacitor is connected to said at least one tool section so as to provide power thereto.  
   
   
       8 . An assembly according to  claim 1  wherein the conductor arrangement comprises a twisted pair of conductors.  
   
   
       9 . An assembly according to  claim 1  wherein the conductor arrangement is a coaxial cable.