Method and Apparatus for Sensing Downhole Characteristics

Abstract

A system for sensing a borehole or formation characteristic at a selected depth while a drill string 12 is in the borehole 36 includes a plurality of sensors 40 to positioned at axially spaced locations along the drill string 12 , and a data transmission system 46 for transmitting signals from each of the plurality of sensors to the surface. A surface computer 22 receives the transmitted signals and determining the sensed characteristics at a selected depth as a function of one of a plurality of sensors positioned along the drill string while at a first selected depth and subsequently another of the plurality of sensors is along the drill string while at substantially the first selected depth.

1 . A system for sensing a selected borehole or formation characteristic at a selected depth while a drill string is in the borehole, comprising:
 a plurality of sensors each positioned at axially spaced locations along the drill string, each of the plurality of sensors sensing the selected borehole or formation characteristic;   a data transmission system for transmitting signals from each of the plurality of sensors to the surface; and   a surface computer for receiving the transmitted signals and determining the sensed characteristic at a selected depth as a function of one of the plurality of sensors positioned along the drill string while at a first selected depth and subsequently another of the plurality of sensors positioned along the drill string while at substantially the first selected depth.   
     
     
         2 . A system as defined in  claim 1 , wherein each of a plurality of sensors senses a spacing to a borehole wall at a selected depth, such that the signals from the plurality of sensors indicate a change in spacing to the borehole wall over time. 
     
     
         3 . A system as defined in  claim 2 , wherein each of a plurality of sensors measures a caliper of the borehole. 
     
     
         4 . A system as defined in  claim 1 , further comprising:
 a surface display for displaying signals from the plurality of sensors.   
     
     
         5 . A system as defined in  claim 1 , wherein signals from each of a plurality of sensors transmitted to the surface computer by a wire conductor spaced along the drill string. 
     
     
         6 . A system as defined in  claim 5 , wherein the transmission system includes:
 a plurality of nodes spaced along the drill string and interfacing with each of a plurality of sensors; and   a plurality of communication links between the nodes.   
     
     
         7 . A system as defined in  claim 1 , wherein the computer distinguishes signals from the plurality of sensors as a function of their spacing along the drill string. 
     
     
         8 . A system as defined in  claim 1 , wherein the sensed characteristic are displayed at the surface as a function of depth. 
     
     
         9 . A system as defined in  claim 1 , wherein at least one of the plurality of sensors is positioned on a bottom hole assembly. 
     
     
         10 . A system as defined in  claim 9 , wherein at least one of the plurality of sensors is positioned on a bit. 
     
     
         11 . A method of sensing a selected borehole or formation characteristic at a selected depth while a drill string is in the borehole, comprising:
 positioning each of a plurality of sensors at axially spaced locations along the drill string;   sensing the selected borehole or formation characteristic with each of the plurality of sensors;   transmitting signals from each of the plurality of sensors to the surface;   receiving the transmitted signals and determining the sensed characteristic at a selected depth as a function of one of the plurality of sensors positioned along the drill string while at a first selected depth and subsequently another of the plurality of sensors positioned along the drill string while at subsequently the first selected depth.   
     
     
         12 . A method as defined in  claim 11 , wherein each of a plurality of sensors senses a spacing to a borehole wall at a selected depth, such that the signals from the plurality of sensors indicate a change in spacing to the borehole wall over time. 
     
     
         13 . A method as defined in  claim 12 , wherein each of a plurality of sensors measures a caliper of the borehole. 
     
     
         14 . A method as defined in  claim 11 , further comprising:
 displaying signals from the plurality of sensors at the surface in substantially real time.   
     
     
         15 . A method as defined in  claim 14 , further comprising:
 displaying a rate of change in the transmitted signals.   
     
     
         16 . A method as defined in  claim 11 , wherein signals from each of the plurality of sensors are transmitted to the computer through a wire conductor along the drill string. 
     
     
         17 . A method as defined in  claim 15 , wherein a signal transmission system includes:
 a plurality of nodes spaced along the drill string and interfacing with each of the plurality of sensors; and   a plurality of communication links between the nodes.   
     
     
         18 . A method as defined in  claim 11 , wherein a computer distinguishes signals from the plurality of sensors as a function of their spacing along the drill string. 
     
     
         19 . The method as defined in  claim 11 , wherein the sensed characteristics are displayed at the surface as a function of the depth.