Downhole Apparatus with Extendable Digitized Sensor Device

Abstract

An apparatus comprising a downhole tool operable to measure a characteristic of a subterranean formation from within a wellbore extending into the subterranean formation. The downhole tool may include a plurality of sensor devices each extendable from a body of the downhole tool by a corresponding pair of arms. Each of the plurality of sensor devices may comprise a plurality of source and measuring electrodes collectively operable to obtain a plurality of measurements pertaining to the characteristic of the subterranean formation, as well as circuitry operable to digitize the plurality of obtained measurements and generate a digital signal corresponding to the characteristic of the subterranean formation

What is claimed is: 
     
         1 . An apparatus, comprising:
 a downhole tool operable to measure a characteristic of a subterranean formation from within a wellbore extending into the subterranean formation, the downhole tool comprising a plurality of sensor devices each extendable from a body of the downhole tool by a corresponding pair of arms, wherein each of the plurality of sensor devices comprises:
 a plurality of source and measuring electrodes collectively operable to obtain a plurality of measurements pertaining to the characteristic of the subterranean formation; and 
 circuitry operable to digitize the plurality of obtained measurements and generate a digital signal corresponding to the characteristic of the subterranean formation. 
   
     
     
         2 . The apparatus of  claim 1  wherein the circuitry of each of the plurality of sensor devices is further operable to transmit the digital signal out of the sensor device. 
     
     
         3 . The apparatus of  claim 1  wherein the circuitry of each of the plurality of sensor devices comprises a clock reference utilized in the digitization of the plurality of obtained measurements. 
     
     
         4 . The apparatus of  claim 1  wherein the circuitry of each of the plurality of sensor devices comprises an analog circuit operable to process the plurality of obtained measurements. 
     
     
         5 . The apparatus of  claim 1  wherein the circuitry of each of the plurality of sensor devices comprises a processor operable to process the digital signal. 
     
     
         6 . The apparatus of  claim 1  wherein the circuitry of each of the plurality of sensor devices comprises a processor operable to process the plurality of digitized obtained measurements. 
     
     
         7 . The apparatus of  claim 1  wherein the circuitry of each of the plurality of sensor devices comprises a power source operable to supply power for at least one of:
 digitizing the plurality of obtained measurements; 
 processing the digital signal; and 
 transmitting the digital signal out of the sensor device. 
 
     
     
         8 . The apparatus of  claim 1  wherein the downhole tool further comprises a controller operable to process multiple digital signals each transmitted from a corresponding one of the plurality of sensor devices. 
     
     
         9 . The apparatus of  claim 8  wherein the controller is further operable to transmit a combined digital signal out of the downhole tool, wherein the combined digital signal is based on the multiple digital signals each transmitted from a corresponding one of the plurality of sensor devices. 
     
     
         10 . The apparatus of  claim 1  wherein the downhole tool comprises a downhole imaging tool. 
     
     
         11 . The apparatus of  claim 10  wherein the downhole imaging tool comprises the plurality of sensor devices, and where the plurality of measuring electrodes of each of the plurality of sensor devices is operable to measure a current from a current path extending through the subterranean formation from at least one of the plurality of source electrodes. 
     
     
         12 . A method, comprising:
 operating each of a plurality of sensor devices of a downhole tool within a wellbore extending into a subterranean formation to obtain a plurality of measurements pertaining to the subterranean formation;   operating each of the plurality of sensor devices to digitize the plurality of measurements obtained by that sensor device;   operating each of the plurality of sensor devices to generate a digital signal based on the plurality of measurements obtained and digitized by that sensor device; and   operating each of the plurality of sensor devices to transmit the generated digital signal out of that sensor device.   
     
     
         13 . The method of  claim 12  wherein operating each of the plurality of sensor devices to digitize the plurality of measurements obtained by that sensor device utilizes a clock reference applied to a measured analog signal corresponding to the plurality of obtained measurements. 
     
     
         14 . The method of  claim 12  further comprising operating each of the plurality of sensor devices to process the generated digital signal within that sensor device before operating each of the plurality of sensor devices to transmit the generated digital signal out of that sensor device. 
     
     
         15 . The method of  claim 12  wherein operating each of the plurality of sensor devices to digitize the plurality of obtained measurements comprises digitizing an analog measurement from each of a plurality of measuring electrodes disposed on that sensor device. 
     
     
         16 . The method of  claim 15  wherein operating each of the plurality of sensor devices to transmit the generated digital signal comprises transmitting a digitized signal representative of the analog measurements from each of the plurality of measuring electrodes. 
     
     
         17 . An apparatus, comprising:
 a downhole tool conveyable within a wellbore extending into a subterranean formation, wherein the downhole tool comprises:
 a body containing a first electronic component; and 
 a plurality of sensor devices each connected to the first electronic component by no more than one electrical conductor, wherein each of the plurality of sensor devices comprises:
 a plurality of electrodes collectively operable to acquire a plurality of measurements pertaining to the formation; and 
 a plurality of second electronic components collectively operable to:
 digitize the acquired plurality of measurements; 
 generate a digital signal based on the digitized acquired plurality of measurements; and 
 transmit the generated digital signal to the first electronic component by the corresponding one electrical conductor. 
 
 
   
     
     
         18 . The apparatus of  claim 17  wherein the plurality of electrodes comprises:
 a plurality of source electrodes each operable to inject electrical current into the formation; and 
 a plurality of measuring electrodes collectively operable to acquire the plurality of measurements, wherein the plurality of measurements pertain to electrical current exiting the formation. 
 
     
     
         19 . The apparatus of  claim 17  further comprising a control system comprising the first electronic component and operable to transmit the generated digital signal received from each of the plurality of sensor devices to outside the downhole tool. 
     
     
         20 . The apparatus of  claim 17  wherein the plurality of sensor devices comprises a first group of sensor devices and a second group of sensor devices, wherein the first group of sensor devices is angularly offset about a longitudinal axis of the downhole tool relative to the second group of sensor devices.