Patent Publication Number: US-2016237809-A1

Title: Downhole Tool Non Contact Position Measurement System

Description:
BACKGROUND 
     This disclosure relates generally to the field of downhole tools and, more particularly, to systems and methods for determining a position of a hub on a downhole tool. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions. 
     In hydrocarbon drilling operations, downhole tools may be lowered into a borehole to perform specific tasks. For example, a logging string system may be lowered through a drill string or downhole tubular. The logging string system includes a logging tool that takes various measurements, which may range from measurements such as pressure or temperature to advanced measurements such as rock properties, fracture analysis, fluid properties in the borehole, or formation properties extending into the rock formation. Some logging tools contact the borehole wall to obtain various measurements. 
     The logging tool may include mechanical linkages and components to facilitate expansion of the logging tool after the logging tool passes through the drill string or downhole tubular. The mechanical linkages are exposed to borehole pressures, as well as fluids having high viscosities or particulates. The borehole environment may degrade the linkages of the logging tool, thereby resulting in more frequent repairs or replacements. 
     SUMMARY OF DISCLOSED EMBODIMENTS 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below. 
     In an embodiment, a downhole tool includes a position system. The position system includes a hub moveably coupled to a fixed tool string. The hub includes a sensor component. The position system also includes a position sensor disposed within the fixed tool string and segregated from the sensor component. Additionally, the sensor component is at a first pressure and the position sensor is at a second pressure, different than the first pressure. 
     In another embodiment, a logging tool may be disposed in a borehole. The logging tool includes a linkage-less caliper tool that moves radially relative to the logging tool. The logging tool also includes a position system that detects a radial position of the caliper tool. 
     In a further embodiment, a method for determining a radial position of a caliper tool includes inducing movement of a hub coupled to the caliper tool. The hub moves in response to radial movement of the caliper tool. The method also includes generating a signal indicative of a hub position via a position sensor. The method further includes determining the radial position of the caliper tool based on the signal indicative of the hub position. 
     Various refinements of the features noted above may exist in relation to various aspects of the present disclosure. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. The brief summary presented above is intended just to familiarize the reader with certain aspects and contexts of embodiments of the present disclosure without limitation to the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  shows a schematic view of an embodiment of a drilling system, in accordance with various embodiments of the present disclosure; 
         FIG. 2  shows a perspective view of an embodiment of a logging tool having a caliper tool, in accordance with various embodiments of the present disclosure; 
         FIG. 3  shows a block diagram of an embodiment of a control system, in accordance with various embodiments of the present disclosure; 
         FIG. 4  shows a partial schematic cross-sectional view of an embodiment of a position system having a magnetoresistive system in a first position, in accordance with various embodiments of the present disclosure; 
         FIG. 5  shows a partial schematic cross-sectional view of the position system of  FIG. 4  in a second position, in accordance with various embodiments of the present disclosure; 
         FIG. 6  shows a partial schematic cross-sectional view of an embodiment of a position system having a linear variable differential transformer in a first position, in accordance with various embodiments of the present disclosure; 
         FIG. 7  shows a partial schematic cross-sectional view of the position system of  FIG. 6  in a second position, in accordance with various embodiments of the present disclosure; 
         FIG. 8  shows a partial schematic cross-sectional view of an embodiment of a position system having a partial reflective system in a first position, in accordance with various embodiments of the present disclosure; 
         FIG. 9  shows a partial schematic cross-sectional view of the position system of  FIG. 8  in a second position, in accordance with various embodiments of the present disclosure; and 
         FIG. 10  shows a flow chart of an embodiment of a method for determining the radial position of a caliper tool, in accordance with various embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present disclosure will be described below. These described embodiments are just examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, some features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions may be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would still be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     Embodiments of the present disclosure are directed toward systems and methods for determining a position of a hub on a downhole tool. In some cases, the axial position of the hub may correspond to a radial position of a mechanical caliper. In examples where the downhole tool includes a caliper, the caliper may include a moveable hub that axially moves along a logging tool as the radial position of the calipers changes. Moreover, the logging tool may include a position sensor to interact with the hub to generate a signal indicative of the axial position of the hub. In certain embodiments, the position sensor includes an array of magnetoresistive sensors that interact with a magnet in the hub. Additionally or alternatively, the position sensor may include a linear variable differential transformer that generate a differential voltage because of the hub position along the logging tool. Moreover, the position sensor may, in certain examples, include a reflective sensor that receive a signal and send a reflected signal back toward a source. 
     As noted above, the axial position of the hub may correspond to a radial position of a mechanical caliper. It should be appreciated, however, that the systems and methods for determining the position of the hub may be used in downhole tools that do not include a caliper, but use the position of the hub in other ways (e.g., an anchoring device, a centralizer, a fishing tool). 
     Referring now to  FIG. 1 , an embodiment of a downhole drilling system  10  (e.g., drilling system) comprises a rig  12  and a drill string  14  coupled to the rig  12 . The drill string  14  includes a drill bit  16  at a distal end that may be rotated to engage a formation and form a borehole  18 . As shown, the borehole  18  includes a borehole sidewall  20  (e.g., sidewall) and an annulus  22  between the borehole  18  and the drill string  14 . Moreover, a bottom hole assembly (BHA)  24  is positioned at the bottom of the borehole  18 . The BHA  24  may include a drill collar  26 , stabilizers  28 , or the like. 
     During operation, drilling mud or drilling fluid is pumped through the drill string  14  and out of the drill bit  16 . The drilling mud flows into the annulus  22  and removes cuttings from a face of the drill bit  16 . Moreover, the drilling mud may cool the drill bit  16  during drilling operations. In the illustrated embodiment, the drilling system  10  includes a logging tool  30 . As shown, the logging tool  30  may extend through the drill bit  16 . The logging tool  30  may conduct downhole logging operations to obtain various measurements in the borehole  18 . For example, the logging tool  30  may include sensors (e.g., resistive, nuclear, photonic, seismic, etc.) to determine various borehole and/or fluidic properties. Additionally, the logging tool  30  may include sampling tools to obtain core samples, fluid samples, or the like from the borehole  18 . Moreover, in certain embodiments, the logging tool  30  may include mechanical measurement devices, such as calipers, to obtain measurements of the borehole  18 . 
     The logging tool  30  may conduct downhole operations while the drill string  14  is positioned within the borehole  18  and while the drill string  14  is being removed from the borehole  18 . For example, the logging tool  30  may be extended through the drill bit  16  and being logging operations. Then, the drill string  14  may be removed from the borehole  18  while the logging tool  30  is extended through the drill bit  16 . While the illustrated embodiment includes a substantially vertical borehole  18 , in other embodiments the borehole  18  may be deviated or substantially horizontal. Additionally, while the illustrated example includes the logging tool  30  extending from the drill bit  16 , in other embodiments, the logging tool  30  may be a separate sub coupled to the drill string  14 . 
       FIG. 2  shows an isometric view of an example of the logging tool  30 . In the illustrated example, the logging tool  30  includes mechanical calipers  32  (e.g., calipers) and sensors  34 . In certain embodiments, the calipers  32  are that expand radially with respect to a logging tool axis  36 . The calipers  32  may contact the sidewall  20  of the borehole  18  to obtain various measurements. For example, the calipers  32  may be used to determine the diameter of the borehole  18 . Additionally, in certain embodiments, the calipers  32  may press the sensors  34  against the sidewall  20  of the borehole  18 , thereby enabling additional measurements (e.g., resistivity, nuclear, photonic, seismic, etc.) of the formation. However, in other embodiments, the sensors  34  may be non-contact sensors and may not contact the sidewall  20  of the borehole  18  to obtain formation measurements. 
     In the illustrated embodiment, the calipers  32  include springs  38  that drive the calipers  32  radially outward with respect to the logging tool axis  36 . That is, the springs  38  are biased to enable expansion of the calipers  32  after the logging tool  30  is extended through the drill bit  16 . However, in other embodiments, the calipers  32  may include mechanical actuators to facilitate deployment of the calipers  32 . For example, the mechanical actuators may block expansion of the calipers  32  until activated. In embodiments where the logging tool  30  extends through the drill bit  16 , the mechanical actuators may block deployment of the calipers  32  until the logging tool  30  is through the drill bit  16 . 
     As shown, the calipers  32  are coupled to the logging tool  30  at a first location  40  and at a second location  42 . The first location  40  is axially farther up the borehole  18  (e.g., closer to the surface) than the second location  42 . As will be described below, the first location  40  may be rigidly fixed to the logging tool  30 . Moreover, the second location  42  may be that move and/or slide axially along the logging tool axis  36 . For example, the second location  42  may be positioned on a hub  44  (e.g., a moveable member) positioned radially about a tool string  46  (e.g., a shaft, a fixed member) of the logging tool  30 . 
     The hub  44  may slide along the tool string  46  in response to the radial expansion and/or compression of the calipers  32 . In certain embodiments, the hub  44  includes rollers, bearings, or the like to facilitate axial movement along the tool string  46 . For example, radial expansion of the calipers  32  drives the hub  44  in a first direction  48  along the logging tool axis  36  (e.g., toward the first location  40 , toward the surface). Additionally, radial compression of the calipers  32  drives the hub  44  in a second direction  50  along the logging tool axis  36  (e.g., away from the first location  40 , toward the bottom of the borehole  18 ). As will be described in detail below, the axial movement of the hub  44  along the logging tool axis  36  may be used to determine the radial position of the calipers  32  via a position system  52 . 
     In the illustrated embodiment, four calipers  32  are coupled to two hubs  44 . As shown, the calipers  32  are positioned approximately  90  degrees offset from the adjacent calipers  32 . As a result, four measurements may be obtained indicative of the radius of the borehole  18 . However, in other embodiments, more or fewer calipers  32  may be utilized. For example, 2, 3, 5, 6, 7, 8, or any suitable number of calipers  32  may be positioned on the tool string  46  to obtain borehole measurements. Moreover, in the illustrated embodiment, each hub  44  is coupled to two calipers  32 , facilitating multiple independent measurements of the borehole  18 . However, in other embodiments, more of fewer hubs  44  may be utilized. For example, each caliper  32  may be independently coupled to a single hub  44 . 
       FIG. 3  is a block diagram of an embodiment of a control system  54  that determine the radial position of the calipers  32  relative to the logging tool axis  36 . The control system  54  includes a controller  56  having a processor  58  and a memory  60 . The memory  60  may include one or more non-transitory (i.e., not merely a signal), computer-readable media, which may include executable instructions that may be executed by the processor  58 . The controller  56  receives a signal from the position system  52  indicative of a position of the hub  44  along the tool string  46 . For example, the position system  52  may include a position sensor  62  that interacts with the hub  44  (e.g., wirelessly, electrically, magnetically, etc.) to determine the position of the hub  44  on the tool string  46 . 
     In the illustrated embodiment, the position system  52  is communicatively coupled to a communication system  64 . The communication system  64  may send a signal to the surface (e.g., to a surface controller) indicative of the radial position of the calipers  32 . In certain embodiments, the communication system  64  includes a telemetry system, a wireless transceiver, a wired communication line (e.g., Ethernet, fiber optic, etc.), or the like to transmit data from the logging tool  30  to the surface. Moreover, the communication system  64  may include a wired or wireless transceiver to receive and/or transmit data between the logging tool  30  and the position system  52  and/or the sensors  34 . The communication system  64  sends the signal to the controller  56  to coordinate drilling, completion, and/or cementing operations. 
       FIG. 4  is a partial schematic cross-sectional view of an embodiment of the position system  52  positioned along the logging tool  30 . In the illustrated embodiment, the position system  52  includes the hub  44  and the position sensor  62 . The position system  52  is communicatively coupled to the communication system  64 , as described above, to transmit data indicative of the position of the hub  44  on the tool string  46 . In the illustrated embodiment, the position sensor  62  includes an array  70  of magnetoresistive sensors  72 . While the illustrated embodiment includes four magnetoresistive sensors  72 , in other embodiments the array  70  may include 1, 2, 3, 5, 6, 7, 8, 9, 10, or any suitable number of magnetoresistive sensors  72 . Additionally, because the magnetoresistive sensors  72  are disposed within the tool string  46 , they may be at a pressure (e.g., a second pressure) substantially equal to atmospheric pressure. In other words, the magnetoresistive sensors  72  may be substantially isolated from the borehole pressure. Moreover, a magnet  74  is positioned within the hub  44 . However, in other embodiments, the magnet  74  may be positioned on the hub  44  and be exposed to borehole pressure (e.g., a first pressure). In certain embodiments, the magnet  74  may be an electromagnetic that transmits a magnetic field toward the array  70 . However, in other embodiments, the magnet  74  may be a permanent or temporary magnet. The magnetoresistive sensors  72  may change a value of electrical resistance in response to the magnetic field transmitted by the magnet  74 . However, as shown, the magnet  74  and the array  70  are segregated from one another. Accordingly, as the hub  44  moves along the hub  44  in the first direction  48  and the second direction  50 , the electrical resistance of the magnetoresistive sensors  72  will change relative to the position of the hub  44 . 
     In the illustrated embodiment, the hub  44  is in a first position  76 . In the first position  76 , the magnet  74  is interacting with the magnetoresistive sensor  72   b . In other words, the magnetic field transmitted by the magnet  74  is changing the electrical resistance of the magnetoresistive sensor  72   b  (e.g., based on resistance measured across the magnetoresistive sensor  72   b ). As a result, the position sensor  62  may send a signal to the communication system  64  indicative of the changed resistance of the magnetoresistive sensor  72   b . Accordingly, the controller  56  may determine the position of the hub  44 . For example, the magnetoresistive sensor  72   b  may correspond to a location on the tool string  46 . Moreover, the position of the hub  44  may correspond to a radial position of the caliper  32 . That is, the caliper  32  may be calibrated to associate different hub positions with associated radial positions of the calipers  32 . 
       FIG. 5  is a partial schematic cross-sectional view of an embodiment of the position system  52 , in which the hub  44  is in a second position  78 . As described above, the magnet  74  in the hub  44  may interact with the magnetoresistive sensors  72  of the array  70 . In the second position  78 , the hub  44  moves in the second direction  50  axially along the logging tool axis  36 , relative to the first position  76 . For example, the calipers  32  may be radially compressed (e.g., due to contact with the sidewall  20 ), thereby driving the hub  44  in the second direction  50 . As a result, the magnet  74  interacts with the magnetoresistive sensor  72 d. As mentioned above, the position of the magnetoresistive sensor  72 d may correspond to a radial position of the calipers  32 . Accordingly, the radial position of the calipers  32  may be determined as the axial position of the hub  44  changes. 
       FIG. 6  is a partial schematic cross-sectional view of an embodiment of the position sensor  62  positioned along the logging tool  30 . As described above, the hub  44  is positioned about the tool string  46  and may move in the first direction  48  and the second direction  50  along the logging tool axis  36 . In the illustrated embodiment, the position sensor  62  includes a linear variable differential transformer (LVDT)  90 . The LVDT  90  includes a primary coil  92 , a top secondary coil  94 , and a bottom secondary coil  96 . Each coil  92 ,  94 ,  96  is wrapped around the interior circumference of the tool string  46 . As shown, the top secondary coil  94  and the bottom secondary coil  96  are electrically coupled via a connecting wire  98 . Moreover, the primary coil  92  is electrically coupled to a power source  100  configured to supply an alternating current to induce a voltage in the top secondary coil  94  and the bottom secondary coil  96  as the hub  44  moves axially along the tool string  46 . In the illustrated embodiment, the hub  44  includes a core  102  configured to induce a voltage across the top secondary coil  94  and the bottom secondary coil  96  which may be measured as a differential at a junction  104 . While the illustrated embodiment  102  depicts the core  102  embedded within the hub  44 , in other embodiments the hub  44  may be the core  102 . 
     In operation, movement of the hub  44  in the first direction  48  and the second direction  50  may induce a voltage at the junction  104 . For example, in the illustrated embodiment, the hub  44  is in the first position  76  and the core  102  is substantially aligned with the primary coil  92 . As a result, the top secondary coil  94  and bottom secondary coil  96  produce substantially equal and opposite voltages, thereby correlating to a differential voltage at the junction  104  of substantially zero. However, movement of the core  102  may induce voltages having different values and/or poles from the top secondary coil  94  and the bottom secondary coil  96 . As a result, the differential voltage at the junction  104  may substantially correspond to the position of the core  102  along the tool string  46 . For example, as described above, the calipers  32  may be calibrated to associate a given differential voltage with the radial position of the calipers  32 . 
       FIG. 7  is a partial schematic cross-sectional view of an embodiment of the position system  52  positioned along the logging tool  30 . As mentioned above, the position system  52  includes the LVDT  90  having the primary coil  92 , the top secondary coil  94 , and the bottom secondary coil  96 . In the illustrated embodiment, the hub  44  is moved in the first direction  48  along the logging tool axis  36  to the second position  78 . For example, the calipers  32  may radially expand relative to the logging tool axis  36 , thereby driving the hub  44  in the first direction  48 . Because the core  102  moves with the hub  44 , voltage in the top secondary coil  94  increases while voltage in the bottom secondary coil  96  decreases. Moreover, because the phase of the voltage across the top secondary coil  94  is the same as the phase of the voltage of the primary coil  92 , the differential voltage measurement at the junction  104  may reveal that the hub  44  has moved in the first direction  48 . Furthermore, movement in the second direction  50  would facilitate a larger voltage across the bottom secondary coil  96  having a phase opposite that of the primary coil  92 . Accordingly, by measuring the differential voltage at the junction  104 , the axial position of the hub  44  along the tool string  46  may be determined. 
     As mentioned above, the measured differential voltage at the junction  104  may be sent to the communication system  64 . The communication system  64  may send the measure differential voltage to the controller  56  for processing. For example, the controller  56  may utilize data stored in the memory  60  to determine that the measured differential voltage correlates to an axial position of the hub  44  on the tool string  46 , and therefore corresponds to the radial position of the calipers  32 . 
       FIG. 8  is a partial schematic cross-sectional view of an embodiment of the position system  52  positioned along the logging tool  30 . In the illustrated embodiment, the position sensor  62  includes a reflective sensor  110 . The reflective sensor  110  includes a source  112  configured to transmit a signal  114  down a wire  116 . For example, the signal  114  may be an electrical impulse. As shown, the hub  44  includes a reflector  118  embedded within the hub  44 . For example, the reflector  118  may be a magnet configured to receive the signal  114  and reflect a reflected signal  120  back to the source  112 . The source  112  may include a receiver configured to receive the reflected signal  120 . In certain embodiments, the source  112  may include a timer configured to determine the time between emission of the signal  114  and reception of the reflected signal  120  to determine the axial position of the reflector  118 . As will be appreciated, the axial position of the reflector  118  corresponds to the axial position of the hub  44 . 
     In operation, the radial position of the calipers  32  drives the hub  44  axially along the logging tool axis  36  in the first direction  48  and the second direction  50 . In the illustrated embodiment, the hub  44  is at the first position  76 . As mentioned above, the first position  76  may correspond to the time elapsed between emitting the signal  114  and receiving the reflected signal  120 , and thereby correspond to the radial position of the calipers  32  (e.g., via information stored in memory  60 ). 
       FIG. 9  is a partial schematic cross-sectional view of an embodiment of the position system  52  positioned along the logging tool  30 . In the illustrated embodiment, the hub  44  is in the second position  78 . In other words, the hub  44  moves axially along the logging tool axis  36  in the first direction  48 . For example, the hub  44  may be driven in the first direction  48  by radial expansion of the calipers  32 . As shown, the reflector  118  is positioned closer to the source  112  than while the hub  44  was in the first position  76 . As a result, the time elapsed between emitting the signal  114  and receiving the reflected signal  120  is reduced, thereby indicating that the hub  44  is closer to the source  112 . As mentioned above, the communication system  64  may send the elapsed time to the controller  56  to evaluate the position of the hub  44  based on the elapsed time. Accordingly, the axial position of the hub  44  may be utilized to determine the radial position of the calipers  32 . 
       FIG. 10  is a flow chart of an embodiment of a method  130  for determining the radial position of the caliper  32 . Movement of the hub  44  is induced at block  132 . For example, the logging tool  30  may be extended through the drill bit  16  and into the borehole  18 . The calipers  32  may be driven to radially expand via the springs  38 . As mentioned above, the calipers  32  are coupled to the hub  44  and radial movement (e.g., expansion or compression) of the calipers  32  drives movement of the hub  44  along the logging tool axis  36 . A signal indicative of the hub position may be generated at block  134 . For example, the hub  44  may interact with the position sensor  62  to produce a signal indicative of the hub position. In certain embodiments, the magnet  74  in the hub  44  may interact with the magnetoresistive sensors  72 . In other embodiments, the hub  44  may induce a differential voltage across the top secondary coil  94  and the bottom secondary coil  96 . Moreover, in other embodiments, the hub  44  may send the reflected signal  120  back to the source  112 . The signal may be received by the communication system and/or the controller  56  at block  136 . For example, as described above, the communication system  64  may be communicatively coupled to the position sensor  62 . Additionally, the communication system  64  may send the signal to the controller  56  for evaluation. The radial position of the calipers  32  is determined at block  138 . For example, the controller  56  may evaluate the signal indicative of the position of the hub  44  via the processor  58  utilizing data stored on the memory  60 . In certain embodiments, the position of the hub  44  corresponds to a radial position of the calipers  32 . For example, the hub position may be compared to a calibrated hub position. As a result, the radial position of the calipers  32  may be determined based on the axial position of the hub  44  along the tool string  46 . 
     As described in detail above, embodiments of the present disclosure are directed toward the position system  52  configured to determine the radial position of the calipers  32 . For example, the position system  52  includes the hub  44  configured to move axially along the logging tool axis  36 . Movement of the hub  44  corresponds to the radial position of the calipers  32 . Moreover, the position system  52  includes the position sensor  62 . In certain embodiments, the position sensor  62  includes the magnetoresistive sensors  72  configured to interact with the hub  44  to produce a signal indicative of the position of the hub  44 . Additionally, in other embodiments, the position sensor  62  includes the LVDT  90  configured to generate a differential voltage based on the position of the hub  44 . Furthermore, in other embodiments, the position sensor  62  includes the reflective sensor  110  configured to indicate the position of the hub  44  based on the time elapsed between the emission of the signal  114  and the reception of the reflected signal  120 . The position of the hub  44  along the tool string  46  may correspond to the radial position of the calipers  32 . As a result, the position of the hub  44  may be utilized to determine the radial position of the calipers  32 . 
     The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.