Patent Publication Number: US-9422806-B2

Title: Downhole monitoring using magnetostrictive probe

Description:
BACKGROUND 
     1. Field of the Disclosure 
     The present invention is related to a method of controlling downhole operations and, in particular, a method of measuring temperatures used in control of equipment used in a wellbore. 
     2. Background of the Art 
     Various downhole operations, such as drilling, production, fracturing operation, etc., generate heat through one or more processes. For example, heat may be generated due to the mechanical action of a drill bit against a wall of a borehole, an explosion used in perforation operations, chemical reactions occurring during a fracking or well stimulation operation, etc. Additionally, various tools along a work string, such as an electric submersible pump, a flow control device, a hydraulic motor, etc. may generate heat. In order to control the performance and production of downhole tools and to operate downhole tools within their specifications, an operator will monitor a downhole temperature. However, most current temperature sensing technologies, including resistance temperature detectors and thermocouple, are only able to provide temperature measurements at a single location in the wellbore. Single location measurements are often insufficient for monitoring these various downhole tools and operations. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect, the present disclosure provides a method of controlling a downhole operation, the method including: controlling a tool to perform the downhole operation at a selected downhole location using a first value of an operation parameter of the tool; using a magnetostrictive probe to determine a temperature profile along a section of a downhole tool or wellbore related to the operation being performed using the first value of the operation parameter; and compare the temperature profile to a selected threshold; and alter the operation parameter to a second value based on the comparison of the temperature profile to the selected threshold. 
     In another aspect, the present disclosure provides an apparatus for controlling an operation downhole, the apparatus including: a tool configured to perform the operation at a downhole location according to an operation parameter of the tool; a magnetostrictive probe extending along a section of tool configured to obtain a temperature profile along the section of the tool related to the operation being performed by the tool; a processor configured to: determine a temperature profile along a section of a downhole tool or wellbore related to the operation using the magnetostrictive probe, compare the temperature profile to a selected threshold, and alter the operation parameter based on the comparison of the temperature profile to the selected threshold. 
     In yet another aspect, the present disclosure provides a system for controlling a downhole operation, the system including: a work string; a tool conveyed by the work string at a downhole location in a wellbore, a tool configured to perform the downhole operation using an operation parameter; a magnetostrictive probe extending along the workstring configured to obtain a temperature profile related to the downhole operation; and a processor configured to: receive the temperature profile from the magnetostrictive probe, compare the temperature profile to a selected threshold, and alter the operation parameter based on the comparison of the temperature profile to the selected threshold. 
     Examples of certain features of the apparatus and method disclosed herein are summarized rather broadly in order that the detailed description thereof that follows may be better understood. There are, of course, additional features of the apparatus and method disclosed hereinafter that will form the subject of the claims appended hereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure herein is best understood with reference to the accompanying figures in which like numerals have generally been assigned to like elements and in which: 
         FIG. 1  shows a downhole system that includes a temperature measurement system for controlling operation of the downhole system in an exemplary embodiment of the disclosure; 
         FIG. 2  shows an exemplary temperature sensor of the downhole system suitable for use in controlling downhole operations in an exemplary embodiment of the present disclosure; 
         FIG. 3  shows a flowchart illustrating a method of controlling operations downhole using temperature measurement obtained using the exemplary temperature sensor of  FIG. 2 ; 
         FIG. 4  shows an exemplary work string including multiple temperature sensors; 
         FIG. 5  shows an exemplary embodiment of a work string in which the temperature sensor is internally disposed within the work sting; and 
         FIG. 6  shows another embodiment in which the temperature sensor is employed in a multi-stage fracturing system. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  shows a downhole system  100  that includes a temperature measurement system for controlling operation of the downhole system  100  in an exemplary embodiment of the disclosure. The downhole system  100  includes a work string  102  disposed in a wellbore  132  formed in a formation  130 . The work string  102  extends in the wellbore  132  from a surface location  104  to a downhole location  106 . The work string  102  may include a drill string, a production string, a fracturing system including a multi-stage fracturing system, a perforation string, etc. A tool  108  for performing a downhole operation is conveyed to a selected depth of the wellbore by the work string  102 . The tool  108  may be an electric submersible pump, a flow control device, a hydraulic motor, or other heat generating downhole tool, for example. The tool  108  may be coupled to a control unit  110  via cable  136 . The control unit  110  controls the tool  108  to perform various downhole operations, such as drilling, fracking or acid stimulation, perforation, production, etc. In various embodiments, the control unit  110  may be at a surface location  104  or at a suitable downhole location in the work string  102 . The control unit  110  includes a processor  112 , a memory location or memory storage device  114  for storing data obtained from the downhole operation of the tool or values of operational parameters of the tool  108 , and one or more programs  116  stored in the memory storage device  114 . When accessed by the processor  112 , the one or more programs  116  enable the processor  110  to perform the methods disclosed herein for controlling operation of the tool  108  using downhole temperature measurements. Temperature measurements may be displayed at display or monitor  140 . The data may be stored downhole or may be sent to the surface without be stored downhole. Processing may therefore occur either downhole or uphole at the surface location  104 . Thus, the methods disclosed herein may be performed in a closed-loop downhole system and in real-time. 
     The work string  102  further includes a temperature sensor  120  for obtaining measurements of temperature at a plurality of locations or depths along the work string  102 . The temperature sensor  120  includes a magnetostrictive transducer  122  and a metal probe  124 . The temperature sensor  120  may be coupled to control unit  110  via cable  138 . The control unit  110  may send signals to activate the temperature sensor  120  and receive from the temperature sensor  120  measurements suitable for determining a temperature map at multiple locations along the metal probe  124 , such as indicted by temperatures T 1 , T 2  and T 3 . The temperature measurements may be obtained at a location exterior to the work string  102  or interior to the work string  102 , in various embodiments. Details of the temperatures sensor  120  are discussed below with respect to  FIG. 2 . 
       FIG. 2  shows an exemplary temperature sensor  120  suitable for use in controlling downhole operations in an exemplary embodiment of the present disclosure. The temperature sensor  120  includes a metal probe  124  and a magnetostrictive transducer (MST)  122  coupled to the metal probe  124 . The metal probe  124  may extend along a section of the work string ( 102 ,  FIG. 1 ) and/or tool ( 108 ,  FIG. 1 ). The temperature sensor  120  may be suitable for determining a temperature at a plurality of locations along the metal probe  124  via an ultrasonic pulse sent longitudinally along the metal probe  124 . In an exemplary embodiment, a diameter of the metal probe  124  may be less than about 1 millimeter (mm) and the length of the metal probe  124  may be about 30 feet (about 10 meters). The metal probe may be made of a material, such as nickel/iron or Inconel, which is rust-resistant and suitable for use a temperatures of downhole environments, such as greater than about 350° Celsius. 
     Notches (n 1 , n 2 , . . . , n N ) are formed at axially spaced-apart locations in the metal probe  124 . The notches often may be separated by a few inches. In general, the notches (n 1 , n 2 , . . . n N ) are circumferential notches that are equally spaced along the longitudinal axis of the metal probe  124  when the temperature of the metal probe  124  is constant along the metal probe  124 . The notches (n 1 , n 2 , . . . n N ) divide the metal probe  124  into segments or intervals ( 202   a ,  202   b , . . . ,  202 N), wherein the intervals may have equal length when the temperature of the metal probe  124  is constant along the metal probe  124 . 
     The MST  122  includes a coil  204  and a magnet  206 , which may be a permanent magnet, contained within a housing  210 . The magnet  206  may be used along with signals in the coil  204  to excite and detect ultrasonic pulses in the metal probe  124 . The magnet  206  and coil  204  served to transform current into an ultrasonic pulse and vice-versa. An end portion  124   a  of the metal probe  124  extends into the housing and the coil  204  is wrapped around the end portion  124   a . The coil  204  is coupled to the control unit  110  via a connector or cable  138 , which may be a coaxial connector, for example. The control unit  110  may provide power and/or electrical signals to the coil  204 . The connector  208  may be of a size suitable for a selected tool or operation. An electrical signal sent from the control unit  110  generates a changing magnetic field, causing magnetostriction at the end portion  124   a  of the metal probe  124  within the housing  210 . The magnetostriction generates an outgoing ultrasonic pulse that propagates from the end portion  124   a  along the length of the metal probe  124  in a direction away from the coil  204 . As the outgoing ultrasonic pulse propagates along the metal probe  124 , each notch (n 1 , n 2 , . . . n N ) reflects a portion or percentage of the outgoing ultrasonic pulse back towards the MST  122 . The remaining portion or percentage of the outgoing ultrasonic pulse continues its propagation along the metal probe  124  away from the coil  204 . A reflected ultrasonic pulse that is received at the MST  124  produces an electrical signal in the coil  204  which is sent to the control unit  110 . Because the metal probe  124  includes a plurality of notches, the control unit  110  records a plurality of reflected signals, each corresponding to a selected notch in the metal probe  124 . 
     As the temperature of the metal probe  124  increase or decreases, the modulus of elasticity of the probe changes and therefore the velocity of sound for the signal propagating through the metal probe  124  increases or decreases with temperature. Thus, determining the travel time between generating a pulse at a first location (e.g., at coil  204 ) and receiving its reflection from a second location (e.g., a selected notch such as notch n 1 ) may be used to determine a temperature at the second location (e.g., notch n 1 ). The increased velocity at elevated temperatures reduces the travel time for the ultrasonic pulse between the first location and the second location. Therefore, the temperature may be determined at a selected notch by determining a travel time between generating the out-going ultrasonic pulse and receiving a reflection from the notch of the generated pulse (i.e., the travel time for the ultrasonic pulse between the first location and the second location), and comparing the determined time to a time interval for an ultrasonic pulse between the first location and the second location at a known reference temperature. Although length of the metal probe  124  may also increase or decrease with temperature, such changes in length are substantially negligible. In another embodiment, since the length of the metal probe  124  changes linearly with temperature within the range of operation temperature of the tool, this length change may be pre-determined and its effect on the travel time of the ultrasonic pulse may be considered in temperature calculations. 
     The control unit  110  may therefore obtain temperature measurements at a plurality of locations (i.e., notches n 1 , n 2 , . . . , n N ) by generating an ultrasonic pulse along the metal probe  124 . The plurality of temperature measurements may be used to determine a temperature profile or a temperature map along a section of the wellbore  132  or work string  102 . The temperature measurements may be related to a downhole operation such as operation of the downhole tool  108 . The control unit  110  may therefore process the temperature measurements and control an operation of tool  108  using the processed temperature measurements. Alternatively, the control unit  110  may store the temperature measurements at the memory storage device  114  for calculations at a later time. 
     In various embodiments, the control unit  110  may monitor the temperature generated by the tool  108  at the selected downhole location using the temperature sensor  120  described herein. In various embodiments, a temperature threshold may be set for controlling the use of the tool. The control unit  110  or processor may then compare at least one of the temperature measurements against a selected threshold and alter an operation parameter of the tool  108  or a downhole operation when the comparison meets a selected criterion. For example, the processor may determine that the temperature profile is greater than the selected threshold or that the temperature profile is less than the selected threshold and control the tool corresponding to results of the comparison. Alternatively, the processor may determine that a subset of the temperature measurements (such as a selected temperature measurement) from the temperature profile is greater than the selected threshold or is less than the selected threshold and control the tool corresponding to results of the comparison. In one embodiment, when a downhole operation generates temperatures above the selected threshold, an operation parameter of the tool may be altered from a first value to a second value in order to maintain the temperature below the selected threshold. In some cases, the tool  108  may be turned off or the downhole operation interrupted when the temperature rises above the selected threshold. 
       FIG. 3  shows a flowchart illustrating a method of controlling operations downhole using temperature measurement obtained using the temperature sensor disclosed herein. In block  302 , an outgoing ultrasonic pulse is generated along the metal probe. The metal probe extends along the work string  102  or a depth interval in the wellbore  132 . In block  304 , a plurality of reflected ultrasonic pulses is received at the control unit  110 . In block  306 , the received plurality of reflected ultrasonic pulses is used to determine a temperature map of the interval of the work string  102  or wellbore  132 . In block  308 , the temperature map may be compared to a selected threshold value. At least one temperature may be compared to the selected threshold value. However, the entire temperature map may also be compared to the selected threshold value. In block  310 , a value of an operational parameter of the tool of a downhole operation is altered when the at least one temperature of the temperature map meets a selected criterion with respect to the selected threshold value. A temperature measurement meeting the selected criterion may include the temperature measurement being greater than the selected threshold value or being less than the selected threshold value, in various embodiments. 
       FIG. 4  shows an exemplary work string  102  including multiple temperature sensors, in one embodiment. As shown in  FIG. 4 , three metal probes  424   a ,  424   b , and  424   c  extend longitudinally along an external surface of the work string. Each metal probe  424   a ,  424   b  and  424   c  has a respective MTS  422   a ,  422   b  and  422   c  associated with it stored in housing  410 . MTS  422   a ,  422   b  and  422   c  send outgoing ultrasonic pulses and receive ultrasonic pulses reflected from notches n 1 , n 2 , n 3  and n 4 , which are located along the downhole tool  108 . Temperature measurements may thus be obtained at multiple circumferential locations around the downhole tool  108 . Three metal probes and four notches in the metal probes are shown only for illustrative purposes, and any number of metal probes as well as any number of notches in the metal probes may be used in various embodiments. 
       FIG. 5  shows an exemplary embodiment of a work string  102  in which the temperature sensor is internally disposed within the work sting  102 . Metal probe  524  of the temperature sensor is disposed within an elastomeric material  506  of a stator  504  of a motor section  502  of the work string  102 . Notches n 1 , n 2 , n 3 , n 4  and n 5  are located along the length of the motor section  502 . Five notches are shown for illustrative purposes only. Any number of notches may be used in various alternate embodiments. Temperature measurements may be obtained at various locations along the motor section  502  via reflection of ultrasonic pulses at notches n 1 , n 2 , n 3 , n 4  and n 5 . Such temperatures may be a result of a heat of friction resulting from operation of the motor section  502 . Measuring the temperature along the motor section  502  may allow a user to change operation of the motor section  502  when one or more of the temperatures becomes too high. 
       FIG. 6  shows another embodiment in which the temperature sensor may be used for a fracking operation. A multi-stage fracturing system  600  is shown along a section of a horizontal borehole. The fracturing system includes exemplary stages  601 ,  603 ,  605  and  607 . At least one stage (e.g., stage  601 ) may include the exemplary temperature sensor  610  of the present disclosure extending along a length of stage  601 . The temperature sensor  610  may be used to obtain a temperature profile along the length of the stage  601  resulting from fracking operations. The temperature profile may thus be used to change a fracking operation at stage  601  by, for example, increasing a rate of introducing acid into the formation, decreasing the rate of introducing acid into the formation, pausing or halting a stimulation operation, changing a stimulation schedule, etc. 
     Therefore in one aspect, the present disclosure provides a method of controlling a downhole operation, the method including: controlling a tool to perform the downhole operation at a selected downhole location using a first value of an operation parameter of the tool; using a magnetostrictive probe to determine a temperature profile along a section of a downhole tool or wellbore related to the operation being performed using the first value of the operation parameter; and compare the temperature profile to a selected threshold; and alter the operation parameter to a second value based on the comparison of the temperature profile to the selected threshold. The magnetostrictive probe includes at least a first notch and a second notch axially separated from each other by a selected interval. Using the magnetostrictive probe may further include generating an ultrasonic pulse at a first location of the magnetostrictive probe, receiving a reflection of the generated ultrasonic pulse from a notch at a second location of the magnetostrictive probe determining a travel time of the ultrasonic pulse between the first location and the second location, determining the temperature at the second location from the determined travel time and a reference travel time for an ultrasonic pulse between the first location and the second location at a known reference temperature. The operation may include, for example, a hydraulic fracturing operation; operation of an artificial lift system; operation of a drill string; operation of a drill bit; operation of a flow control device; operation of a hydraulic motor; operation of a perforating system; and a wellbore or formation temperature monitoring operation. A selected temperature measurement from the temperature profile may be compared to the selected threshold value and the operation parameter may be altered to the second value based on the comparison of the selected temperature to the selected threshold. Comparing the temperature profile to the selected threshold may also include one of: (i) determining the temperature profile to be greater than the selected threshold; (ii) determining the temperature profile to be less than the selected threshold; (iii) determining a selected temperature measurement from the temperature profile to be greater than the selected threshold; and (iv) determining a selected temperature measurement from the temperature profile to be less than the selected threshold. In various embodiments, the magnetostrictive probe is made of a material resistant to rust in a downhole environment. 
     In another aspect, the present disclosure provides an apparatus for controlling an operation downhole, the apparatus including: a tool configured to perform the operation at a downhole location according to an operation parameter of the tool; a magnetostrictive probe extending along a section of tool configured to obtain a temperature profile along the section of the tool related to the operation being performed by the tool; a processor configured to: determine a temperature profile along a section of a wellbore related to the operation using the magnetostrictive probe, compare the temperature profile to a selected threshold, and alter the operation parameter based on the comparison of the temperature profile to the selected threshold. The magnetostrictive probe generally includes at least a first notch and a second notch axially separated from each other by a selected interval. The processor activates a transducer to generate an ultrasonic pulse at a first location of the magnetostrictive probe, receives a signal from the transducer related to a reflection of the generated ultrasonic pulse from a notch at a second location of the magnetostrictive probe, determines a travel time of the ultrasonic pulse between the first location and the second location, and determines the temperature at the second location from the determined travel time and a reference travel time for an ultrasonic pulse between the first location and the second location at a known reference temperature. The tool may be at least one of: a hydraulic fracturing system; an artificial lift system; a drill string; a drill bit; a flow control device; a hydraulic motor; a perforating system; and a downhole tool. The processor may also compare a selected temperature measurement from the temperature profile to the selected threshold value and alter the operation parameter based on the comparison of the selected temperature to the selected threshold. Also, the processor may compare the temperature profile to the selected threshold by performing at least one of: (i) determining the temperature profile to be greater than the selected threshold; (ii) determining the temperature profile to be less than the selected threshold; (iii) determining a selected temperature measurement from the temperature profile to be greater than the selected threshold; and (iv) determining a selected temperature measurement from the temperature profile to be less than the selected threshold. The magnetostrictive probe may include a material encapsulated by either an anti-corrosion material or an anti-scaling material or both. 
     In yet another aspect, the present disclosure provides a system for controlling a downhole operation, the system including: a work string; a tool conveyed by the work string at a downhole location in a wellbore, a tool configured to perform the downhole operation using an operation parameter; a magnetostrictive probe extending along the workstring configured to obtain a temperature profile related to the downhole operation; and a processor configured to: receive the temperature profile from the magnetostrictive probe, compare the temperature profile to a selected threshold, and alter the operation parameter based on the comparison of the temperature profile to the selected threshold. The magnetostrictive probe may include at least a first notch and a second notch axially separated from each other by a selected interval. The processor activates a transducer to generate an ultrasonic pulse at a first location of the magnetostrictive probe, receives a signal from the transducer related to a reflection of the generated ultrasonic pulse from a notch at a second location of the magnetostrictive probe, determine a travel time of the ultrasonic pulse between the first location and the second location, and determines the temperature at the second location from the determined travel time and a reference travel time for an ultrasonic pulse between the first location and the second location at a known reference temperature. In various embodiments, the tool may be at least one of: a hydraulic fracturing system; an artificial lift system; a drill string; a drill bit; a flow control device; a hydraulic motor; a perforating system; and a downhole tool. The processor is may compare an individual temperature measurement from the temperature profile to the selected threshold value and alter the operation parameter based on the comparison of the temperature profile to the selected threshold. Also, the processor may compare the temperature profile to the selected threshold by performing at least one of: (i) determining the temperature profile to be greater than the selected threshold; (ii) determining the temperature profile to be less than the selected threshold; (iii) determining a selected temperature measurement from the temperature profile to be greater than the selected threshold; and (iv) determining a selected temperature measurement from the temperature profile to be less than the selected threshold. 
     While the foregoing disclosure is directed to the certain exemplary embodiments of the disclosure, various modifications will be apparent to those skilled in the art. It is intended that all variations within the scope and spirit of the appended claims be embraced by the foregoing disclosure.