Simplified measurement of borehole fluid resistivity

Abstract

A well logging system that includes a tool which is deployed within the well. The tool has a housing in which imaging hardware is stored, and on which sensors are located, where the sensors detect and measure electrical signals that have been induced in the formation surrounding the well. A wiper system is also mounted on the housing for clearing mud and other debris from outer surfaces of the sensors.

What is claimed is: 
     
         1 . A tool for imaging in a subterranean wellbore comprising:
 a housing;   a sensor coupled with the housing that is in selective electrical communication with a formation intersected by the wellbore; and   a wiper system having a wiper blade for selectively clearing a foreign substance from a surface of the sensor.   
     
     
         2 . The tool of  claim 1 , wherein the wiper system further comprises a wiper rod that selectively reciprocates in a direction substantially parallel with an axis of the housing, and wherein the wiper blade is mounted in a wiper arm that is transversely coupled to the wiper rod. 
     
     
         3 . The tool of  claim 2 , wherein the wiper system further comprises a motor selectively moving the wiper blade across the surface of the sensor. 
     
     
         4 . The tool of  claim 2 , wherein the sensor comprises a planar electrode set. 
     
     
         5 . The tool of  claim 1 , wherein the wiper blade is helically shaped and rotatable about the housing, so that when fluid flows axially past the housing, the fluid exerts a rotational force onto the wiper blade thereby causing the wiper blade to wipe across the surface of the sensor along a circular path. 
     
     
         6 . The tool of  claim 5 , wherein opposing ends of the wiper blade are coupled with supports that rotate in a plane transverse to an axis of the housing. 
     
     
         7 . The tool of  claim 5 , wherein the sensor comprises a cylindrical electrode set. 
     
     
         8 . The tool of  claim 1 , further comprising a transducer for creating an electrical field in and adjacent the wellbore. 
     
     
         9 . A tool for imaging in a subterranean wellbore comprising:
 a housing;   sensors coupled with the housing having a surface in communication with fluid in the wellbore; and   a pliable wiper blade selectively moveable across the surface and in contact with the surface so that the blade removes matter from the wellbore that adheres to the surface.   
     
     
         10 . The tool of  claim 9 , wherein the wiper blade comprises polyether-ether-ketone. 
     
     
         11 . The tool of  claim 9 , further comprising a wiper arm for holding the wiper blade. 
     
     
         12 . The tool of  claim 9 , further comprising a wiper assembly for reciprocating the wiper blade along a path substantially parallel with an axis of the housing. 
     
     
         13 . The tool of  claim 9 , further comprising a frame with a helical shaped arm in which the wiper blade is mounted and members coupled on opposing ends of the arm that rotationally mount the frame to the housing and so that when a fluid in the wellbore flows past the frame, a rotational force rotates the helical shaped arm and causes the wiper blade to sweep across the surfaces of the sensors.