Patent Publication Number: US-7595737-B2

Title: Shear coupled acoustic telemetry system

Description:
BACKGROUND 
     The present invention relates generally to equipment utilized and operations performed in conjunction with wireless telemetry and, in an embodiment described herein, more particularly provides a shear coupled acoustic telemetry system for use with a subterranean well. 
     Typical acoustic telemetry systems used in subterranean wells include at least one stack of piezoceramic elements, or other electromagnetically active elements (piezoelectrics, magnetostrictives, electrostrictives, voice coil, etc.) to generate axial stress waves in a wall of a tubular string. This due to the fact that it is generally considered that axial stress waves are less attenuated as compared to other types of stress waves (torsional, flexural, surface, etc.) in a tubular string positioned in a wellbore environment. 
     Thus, past acoustic telemetry systems have tended to use transmitters which are axially inline with the tubular string wall for most efficient axial coupling between the transmitter and the wall. To maximize the volume of the electromagnetically active elements, the transmitter is usually positioned in an annular cavity internal to the tubular string wall, with annular-shaped elements axially inline with the wall and concentric with the tubular string. 
     However, such configurations pose certain problems. For example, tubular strings used in wellbores typically have very limited thickness in their walls, providing only limited available volume for acoustic transmitters. As another example, each different size of tubular string requires that a different-sized transmitter be designed specifically for that tubular string, which eliminates any possibility of interchangeability between transmitters and tubular strings. Furthermore, axially coupled transmitters are not well suited for taking advantage of other modes of transmission (such as flexural, torsional, shear, etc.) or multi-mode combinations, which may be more advantageous for short distance acoustic transmission. 
     SUMMARY 
     In carrying out the principles of the present invention, an acoustic telemetry system is provided which solves at least one problem in the art. One example is described below in which the system utilizes shear coupling to transmit acoustic signals from a transmitter to a wall of a tubular string. Another example is described below in which the transmitter is contained within its own pressure-bearing housing which is positioned external to the tubular string wall. 
     In one aspect of the invention, an acoustic telemetry system is provided which includes a tubular string having a pressure-bearing wall, and an acoustic signal transmitter. The transmitter is positioned external to the wall, and is operative to transmit an acoustic signal to the wall. The transmitter may be positioned external to the wall without necessarily being external to the tubular string itself. 
     In another aspect of the invention, an acoustic telemetry system includes an acoustic signal transmitter shear coupled to a pressure-bearing wall of a tubular string, with the transmitter being operative to transmit an acoustic signal to the wall. The shear coupling (transmission of shear force between surfaces) may be enhanced by use of clamps, adhesive bonding, roughened or serrated surfaces, magnets, fasteners, etc. 
     In yet another aspect of the invention, an acoustic telemetry system includes an acoustic signal transmitter contained within a pressure-bearing housing positioned external to a pressure-bearing wall of a tubular string and operative to transmit an acoustic signal to the wall. The transmitter housing may be shear coupled to the tubular string wall. 
     These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings, in which similar elements are indicated in the various figures using the same reference numbers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic partially cross-sectional view of a well system embodying principles of the present invention; 
         FIG. 2  is an enlarged scale schematic cross-sectional view of a configuration of a downhole transmitter portion of an acoustic telemetry system in the well system of  FIG. 1 ; 
         FIG. 3  is a schematic cross-sectional view of the configuration of the downhole transmitter portion of the acoustic telemetry system, taken along line  3 - 3  of  FIG. 2 ; 
         FIG. 4  is an enlarged scale schematic cross-sectional view of an alternate configuration of the downhole transmitter portion of the acoustic telemetry system; 
         FIG. 5  is a further enlarged scale schematic cross-sectional view of the downhole transmitter portion of the acoustic telemetry system. 
         FIG. 6  is a schematic partially cross-sectional view of a first alternate construction of the downhole transmitter portion of the acoustic telemetry system; and 
         FIG. 7  is a schematic elevational view of a second alternate construction of the downhole transmitter portion of the acoustic telemetry system. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present invention. The embodiments are described merely as examples of useful applications of the principles of the invention, which is not limited to any specific details of these embodiments. 
     In the following description of the representative embodiments of the invention, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. In general, “above”, “upper”, “upward” and similar terms refer to a direction toward the earth&#39;s surface along a wellbore, and “below”, “lower”, “downward” and similar terms refer to a direction away from the earth&#39;s surface along the wellbore. 
     Representatively illustrated in  FIG. 1  is a well system  10  which embodies principles of the present invention. The well system  10  includes an acoustic telemetry system  12  for communicating data and/or control signals between downhole and surface locations. 
     The telemetry system  12  includes a downhole transmitter assembly  14  and a surface receiver assembly  16 . However, it should be clearly understood that the transmitter assembly  14  may also include a receiver, and the receiver assembly  16  may also include a transmitter, so that either one of these is in effect a transceiver. 
     Furthermore, the telemetry system  12  could include other or different components not illustrated in  FIG. 1 , such as one or more repeaters for relaying signals between the transmitter assembly  14  and the receiver assembly  16 , etc. Either or both of the transmitter assembly  14  and receiver assembly  16  may be incorporated into other components, such as a repeater, another type of well tool, etc. 
     The transmitter assembly  14  is preferably connected to a downhole device  18 . The connection between the device  18  and the transmitter assembly  14  may be hardwired as depicted in  FIG. 1 , or it may be wireless. 
     The device  18  may be, for example, a sensor for sensing a downhole parameter (such as temperature, pressure, water cut, resistivity, capacitance, radioactivity, acceleration, displacement, etc.), an actuator for a well tool, or any other type of device for which data and/or control signals would be useful for communication with the receiver assembly  16 . The device  18  may be incorporated into the transmitter assembly  14 . 
     A tubular string  20  extends between the transmitter assembly  14  and the receiver assembly  16 . The telemetry system  12  provides for communication between the transmitter and receiver assemblies  14 ,  16  by transmission of stress waves through a pressure-bearing wall  22  of the tubular string  20 . 
     Although the tubular string  20  is depicted in  FIG. 1  as being a tubing string positioned within an outer casing or liner string  24 , this example is provided only for illustration purposes, and it should be clearly understood that many other configurations are possible in keeping with the principles of the invention. For example, the tubular string  20  could instead be a casing or liner string, which may or not be cemented in a wellbore  26  of the well system  10 . As another alternative, the tubular string  20  could be positioned in an open, rather than a cased, wellbore. 
     Although the transmitter assembly  14  and downhole device  18  are depicted in  FIG. 1  as being positioned external to the tubular string  20 , other configurations are possible in keeping with the principles of the invention. For example, the transmitter assembly  14  and/or the device  18  could be internal to the tubular string  20  (such as, positioned in an internal flow passage  42  of the tubular string as illustrated in  FIG. 4 ), the device could be positioned within the wall  22  of the tubular string, etc. 
     The receiver assembly  16  is preferably positioned at a surface location, but other locations are possible in keeping with the principles of the invention. For example, if the receiver assembly  16  is incorporated into a repeater or other type of well tool, then the receiver assembly may be positioned downhole, in a subsea wellhead, internal or external to the tubular string  20  (as described herein for the transmitter assembly  14 ), etc. 
     The receiver assembly  16  as depicted in  FIG. 1  includes an acoustic signal detector  28  (such as an accelerometer or other sensor, e.g., including a piezoceramic or other electromagnetically active elements, etc.) and electronic circuitry  30  for receiving, recording, processing, interpreting, displaying, and otherwise dealing with the received acoustic signals. These components are well known in the art and are not further described herein. 
     Referring additionally now to  FIG. 2 , an enlarged scale view of the downhole portion of the telemetry system  12  is representatively illustrated. In this view it may be clearly seen that the transmitter assembly  14  is positioned external to the pressure-bearing wall  22  of the tubular string  20 . The transmitter assembly  14  is not axially inline with any portion of the wall  22 , and is not received in any recess or cavity formed in the wall. 
     Instead, the transmitter assembly  14  is shear coupled to the wall  22 , as described more fully below. This unique positioning of the transmitter assembly  14  provides many advantages. For example, the transmitter assembly  14  is not limited to the available cross-sectional area of the wall  22 , the transmitter assembly can be used with various sizes of tubular strings, the transmitter assembly can effectively transmit acoustic signal modes other than axial (such as flexural, which is particularly useful for short distance communication), etc. 
     As depicted in  FIG. 2 , the transmitter assembly  14  includes electronic circuitry  32 , an acoustic transmitter  34  and a power source  36  (such as a battery or downhole generator, etc.). These components are preferably (but not necessarily) contained within a pressure-bearing housing  38  which is attached to the wall  22  of the tubular string  20 . 
     The electronic circuitry  32  is used for communicating with the device  18  and operating the transmitter  34 . The power source  36  is used for supplying electrical power to operate the circuitry  32  and the transmitter  34 . 
     The acoustic transmitter  34  is preferably of the type which includes a stack of piezoceramic or other electromagnetically active elements, as described more fully below. Note that the transmitter  34  is external to the wall  22  of the tubular string  20 , and is not concentric with the tubular string. 
     Referring additionally now to  FIG. 3 , another cross-sectional view of the downhole portion of the telemetry system  12  is representatively illustrated. In this view it may be seen that the contact between the housing  38  and the wall  22  of the tubular string  20  is only at a single point  40  in transverse cross-section. However, the housing  38  and/or wall  22  could be otherwise configured to provide a larger contact surface area for shear coupling therebetween. 
     In this view it may again be seen that the transmitter assembly  14  is external to both the wall  22  and an internal flow passage  42  of the tubular string  20 . The transmitter assembly  14  could, however, be positioned within the flow passage  42  and remain external to the wall  22 . 
     We can also see from this view that there is a reduced contact area between the transmitter assembly  14  and the wall  22 . Acoustic energy travels from the transmitter assembly  14  to the wall  22  through this reduced contact area. 
     As used herein, the term “reduced contact area” is used to indicate a line contact or a point contact. A line contact is contact between surfaces wherein a ratio of length to width of the contact is greater than or equal to four. A point contact exists when the area of the contact is less than or equal to half of the total cross-sectional area (taken transverse to the longitudinal axis) of the smaller component, in this case the housing  38  of the transmitter assembly  14 . 
     Referring additionally now to  FIG. 4 , an alternate configuration of the downhole portion of the telemetry system  12  is representatively illustrated. In this configuration, the transmitter assembly  14  is positioned within the passage  42 , but is still external to the wall  22  of the tubular string  20 , since the transmitter is not axially inline with the wall, is not positioned in a cavity in the wall, etc. Instead, the housing  38  is attached and shear coupled to an inner surface of the wall  22 . 
     Referring additionally now to  FIG. 5 , a further enlarged and more detailed cross-sectional view of the transmitter assembly  14  is representatively illustrated. In this view it may be seen that the transmitter  34  includes a stack of electromagnetically active disc-shaped elements  44  within the housing  38 . A compressive preload is applied to the elements  44  by nuts  46 ,  48  or another preload biasing device. However, it should be understood that it is not necessary to apply a preload to the elements  44  in keeping with the principles of the invention. 
     Preferably, a spherical load transfer device  50  is used between the elements  44  and one or both of the preload nuts  46 ,  48 . The construction and advantages of the load transfer device  50  are more fully described in U.S. application Ser. No. 11/459,398, filed Jul. 24, 2006, and the entire disclosure of which is incorporated herein by this reference. The transmitter  34  may also utilize the thermal expansion matching and acoustic impedance matching techniques described in the incorporated application. 
     To enhance the shear coupling between the housing  38  and the wall  22  of the tubular string  20 , external mating surfaces  52 ,  54  of the housing and wall may be roughened, serrated, etc. to provide increased “grip” therebetween. This enhanced shear coupling may be provided in addition to attachment of the housing  38  to the wall  22  using adhesive bonding, fasteners, clamps, etc. 
     Referring additionally now to  FIG. 6 , another alternate configuration of the downhole portion of the telemetry system  12  is representatively illustrated. In this configuration, an electrically insulating layer  56  is positioned between the mating surfaces  52 ,  54  of the housing  38  and wall  22 . The layer  56  isolates the transmitter assembly  14  from spurious electrical currents which may be produced in the tubular string  20  due to various phenomena. 
     Electrically insulating layers may also be used within the transmitter assembly  14  itself, either in addition or as an alternative to the layer  56 . For example, the elements  34  could be isolated from the housing  38  using an insulating layer within the housing. 
     It should be understood, however, that there could be metal-to-metal contact between the housing  38  and the wall  22 , if desired. For example, in the configuration depicted in  FIG. 5 , it may be desirable for there to be metal-to-metal contact between the surfaces  52 ,  54 . Of course, an electrically insulating layer could be used between the surfaces  52 ,  54  in the configuration of  FIG. 5 , if desired. 
     Referring additionally now to  FIG. 7 , another alternate configuration of the downhole portion of the telemetry system  12  is representatively illustrated. In this alternate configuration, an inclined structure  58  is provided at an upper end of the transmitter assembly  14 . A similar structure may be provided at the lower end of the transmitter assembly  14  in addition, or as an alternative, to the structure  58 . 
     The structure  58  may perform any of several functions. For example, the structure  58  may protect the transmitter assembly  14  from damage during conveyance in the wellbore  26 , the structure may provide a passage  60  for pressure or wired communication with the device  18 , the flow passage  42 , etc., and may in some embodiments provide some axial acoustic transmission to the wall  22  of the tubular string  20 . 
     However, preferably the main acoustic coupling between the housing  38  and the wall  22  of the tubular string  20  is via shear coupling. Depicted in  FIG. 7  is another manner of ensuring shear force transmission between the housing  38  and the wall  22  in the form of a band clamp  62  which encircles the housing and wall. The clamp  62  applies a normal force between the surfaces  52 ,  54  to thereby enhance the frictional shear coupling therebetween. Note that any manner of applying a normal force between the surfaces  52 ,  54  or otherwise increasing shear coupling between the surfaces may be used in keeping with the principles of the invention. 
     It may now be fully appreciated that the acoustic telemetry system  12  described above provides a variety of benefits, including cost-effective and convenient use of the transmitter  34  with various sizes of tubular strings, ability to effectively transmit acoustic stress waves other than or in addition to axial (such as flexural, surface, torsional, multi-mode, etc.), modular construction, volume unlimited by tubular string wall, etc. The transmitter  34  is advantageously not concentric with the tubular string  20 , but is instead positioned external to the wall  22  of the tubular string. 
     As discussed above, the transmitter assembly  14  could include a receiver, so that the transmitter assembly could alternatively be described as a transceiver. In that case, the elements  44  (or other electromagnetically active elements, other types of sensors, etc.) could be used to receive or otherwise sense stress waves transmitted through the tubular string  20  from another location. In this manner, signals could be either transmitted to or from the transmitter assembly  14 . The term “acoustic telemetry assembly” is used herein to indicate a transmitter assembly (such as the transmitter assembly  14 ), a receiver assembly (such as the receiver assembly  16 ) or a combination thereof. 
     Although several specific embodiments of the invention have been separately described above, it should be clearly understood that any, or any combination, of the features of any of these embodiments may be incorporated into any of the other embodiments in keeping with the principles of the invention. 
     Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to these specific embodiments, and such changes are within the scope of the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims and their equivalents.