Thermography logging tool

Abstract

The invention relates to a logging tool for determining the properties of a fluid surrounding the tool arranged downhole in a casing comprising a wall and having a longitudinal extension. The logging tool has a substantially longitudinal cylindrical shape with a longitudinal axis, and the logging tool comprises a sensor unit comprising an anemometer having a resistance probe electrically connected with three other resistors, a voltmeter and an amplifier for forming a bridge circuit, such as a Wheatstone bridge, having bridge current and bridge voltage. The invention further relates to a method for determining the properties of a fluid by means of the logging tool.

1 . A logging tool ( 1 ) for determining the properties of a fluid ( 2 ) surrounding the tool arranged downhole in a casing ( 3 ) comprising a wall ( 4 ) and having a longitudinal extension and a longitudinal axis (t), wherein the logging tool comprises:
 a sensor unit ( 5 ) comprising an anemometer ( 6 ) having a resistance probe ( 7 , R 1 ) electrically connected with three other resistors (R 2 , R 3 , R 4 ), a voltmeter (V) and an amplifier ( 25 ) for forming a bridge circuit, such as a Wheatstone bridge, having a first and a second bridge voltage,   
       wherein the sensor unit comprises switches ( 8 ) for disconnecting or connecting the amplifier and connecting or disconnecting a voltage supply. 
     
     
         2 . A logging tool according to  claim 1 , wherein the anemometer is a hot wire anemometer or a hot film anemometer. 
     
     
         3 . A logging tool according to  claim 1 , wherein the probe is arranged on an outer face ( 20 ) of the tool. 
     
     
         4 . A logging tool according to  claim 1 , wherein the sensor unit comprises a plurality of anemometers all having a resistance probe. 
     
     
         5 . A logging tool according to  claim 1 , wherein the probes are arranged on the outer face of the tool. 
     
     
         6 . A logging tool according to  claim 1 , wherein the tool comprises at least one thermocouple ( 18 ) arranged partly on the outer face of the tool. 
     
     
         7 . A logging tool according to  claim 1 , wherein the tool comprises a plurality of electrodes ( 16 ) arranged spaced apart around the longitudinal axis in the periphery of the tool, enabling the fluid to flow between the electrodes and the casing wall. 
     
     
         8 . A logging tool according to  claim 1 , further comprising a positioning device ( 22 ) for determining a position of the logging tool along the longitudinal extension of the casing. 
     
     
         9 . A logging tool according to  claim 1 , wherein
 a temperature of the probe resistance is maintained constant by varying the current by means of the amplifier so that a first bride voltage is substantially zero when a first measurement of a second bridge voltage is performed by the voltmeter, and   the second bridge voltage is an alternating voltage when a second measurement of the first bridge voltage is performed.   
     
     
         10 . A logging tool according to  claim 9 , wherein the second bridge voltage is maintained constant at a value different from zero by the voltage supply when a third measurement of the first bridge voltage is performed. 
     
     
         11 . A logging tool according to  claim 9 , wherein a third measurement is performed using the thermocouples. 
     
     
         12 . A logging tool according to  claim 9 , wherein the alternating voltage or alternating current have sine, square, rectangular, triangle, ramp, spiked or sawtooth waveforms. 
     
     
         13 . A method for determining the properties of a fluid ( 2 ) by means of the logging tool according to  claim 1 , comprising the steps of:
 submerging the logging tool into a casing,   maintaining a constant temperature in the resistance probe by varying the current,   increasing the bridge current by means of the amplifier if the temperature in the resistance probe decreases until a first bridge voltage is substantially zero,   measuring a second bridge voltage by means of the voltmeter,   disconnecting the amplifier and the voltage supply and connecting a second voltmeter by means of the switches,   providing the second bridge voltage as an alternating voltage, and   measuring the first bridge voltage by means of the second voltmeter.   
     
     
         14 . Use of the logging tool according to  claim 1  for determining the fluid properties of a fluid in a well downhole. 
     
     
         15 . A detection system comprising a logging tool according to  claim 1  and a calculation unit for processing capacitance measurements performed by the electrodes and/or a driving unit for moving the tool forward in the casing.