Low-frequency viscosity, density, and viscoelasticity sensor for downhole applications

Abstract

Disclosed is an apparatus for estimating a property of a fluid downhole. The apparatus includes a carrier configured to be conveyed through a borehole penetrating the earth. A cantilever is disposed at the carrier and configured to move in the fluid upon receiving a stimulus. An actuator is disposed at the cantilever and configured to provide the stimulus at a frequency less than a lowest resonant frequency of the cantilever. A sensor is disposed at the cantilever and configured to sense a strain imposed on the cantilever due to movement of the cantilever in the fluid in order to estimate the property.

1 . An apparatus for estimating a property of a fluid downhole, the apparatus comprising:
 a carrier configured to be conveyed through a borehole penetrating the earth;   a cantilever disposed at the carrier and configured to move in the fluid upon receiving a stimulus force;   an actuator disposed at the cantilever and configured to provide the stimulus force at a frequency less than a lowest resonant frequency of the cantilever; and   a sensor disposed at the cantilever and configured to sense a strain imposed on the cantilever due to movement of the cantilever in the fluid in order to estimate the property.   
     
     
         2 . The apparatus according to  claim 1 , wherein the property comprises at least one of density, viscosity, and visco elasticity. 
     
     
         3 . The apparatus according to  claim 1 , wherein the frequency is zero Hertz. 
     
     
         4 . The apparatus according to  claim 3 , further comprising a feedback control circuit configured to receive the strain as input and to control a signal to the actuator to maintain the strain at a constant value wherein a change in magnitude of the signal necessary to maintain the strain at the constant value is used to derive viscosity or density of the fluid. 
     
     
         5 . The apparatus according to  claim 1 , wherein the cantilever and a base supporting the cantilever is formed from a substrate. 
     
     
         6 . The apparatus according to  claim 1 , wherein the cantilever defines a first hole and a second hole with a center bridge element disposed between the holes, the cantilever further defining a first side bridge element adjacent to the first hole and a second side bridge element adjacent to the second hole, the first, second, and center bridge elements extending from a base to a distal end of the cantilever. 
     
     
         7 . The apparatus according to  claim 6 , wherein the sensor is disposed at the center bridge element. 
     
     
         8 . The apparatus according to  claim 6 , wherein sensor comprises a first sensor disposed at the first side bridge element, a second sensor disposed at the second side bridge element, and a third sensor disposed at the center bridge element. 
     
     
         9 . The apparatus according to  claim 6 , wherein the actuator comprises a conductive element extending from the first side bridge element to the second side bridge element and configured to conduct current to interact with a magnetic field in order to move the cantilever. 
     
     
         10 . The apparatus according to  claim 6 , wherein the actuator comprises a layer of magnetic material extending from the first side bridge element to the second side bridge element and configured to interact with a magnetic field in order to move the cantilever. 
     
     
         11 . The apparatus according to  claim 1 , wherein the actuator comprises at least one of a piezoelectric material, a conductive material, a magnetostrictive material, and a photostrictive material. 
     
     
         12 . The apparatus according to  claim 11 , wherein the conductive material is configured to conduct current that interacts with a magnetic field to move the cantilever. 
     
     
         13 . The apparatus according to  claim 12 , wherein the actuator further comprises a source of the magnetic field configured to interact with a current or magnetic material disposed at the cantilever in order to move the cantilever. 
     
     
         14 . The apparatus according to  claim 1 , further comprising an electronic device coupled to the actuator and configured to actuate the actuator at the frequency less than the lowest resonant frequency of the cantilever. 
     
     
         15 . The apparatus according to  claim 14 , wherein the electronic device is configured to provide at least one of a voltage, a current, and light to actuate the actuator. 
     
     
         16 . The apparatus according to  claim 1 , wherein the sensor comprises a strain gauge. 
     
     
         17 . The apparatus according to  claim 16 , where in the strain gauge uses a change in resistance or a magnetostrictive effect to measure the strain. 
     
     
         18 . The apparatus according to  claim 1 , wherein the carrier comprises at least one of a wireline, a slickline, a drillstring, and coiled tubing. 
     
     
         19 . A method for estimating a property of a fluid downhole, the method comprising:
 conveying a carrier through a borehole penetrating the earth;   moving a cantilever in the fluid with an actuator at a frequency less than a lowest resonant frequency of the cantilever, the cantilever being disposed at the carrier; and   sensing a strain imposed on the cantilever due to movement of the cantilever in the fluid using a sensor in order to estimate the property.   
     
     
         20 . The method according to  claim 19 , wherein the property comprises at least one of density, viscosity, and viscoelasticity. 
     
     
         21 . The method according to  claim 19 , wherein sensing comprises measuring the strain as a function of time with respect to a stimulus applied to the cantilever by the actuator. 
     
     
         22 . The method according to  claim 19 , wherein the frequency comprises a first frequency and a second frequency and the strain comprises a first strain corresponding to movement of the cantilever at the first frequency and a second strain corresponding to movement of the cantilever at the second frequency, the first strain and the second strain being used to identify the fluid and to estimate viscoelasticity of the fluid. 
     
     
         23 . A non-transitory computer-readable medium comprising computer-executable instructions for estimating a property of a fluid downhole by implementing a method comprising:
 moving a cantilever in the fluid with an actuator at a frequency less than a lowest resonant frequency of the cantilever, the cantilever being disposed at the carrier configured to be conveyed through a borehole penetrating the earth; and   sensing a strain imposed on the cantilever due to movement of the cantilever in the fluid using a sensor in order to estimate the property.