Abstract:
An annular coupler for transmitting data across a tool joint may include a first coupler segment spanning a first portion of the circumference of the annular coupler. The annular coupler may further include a second coupler segment, electrically insulated from the first coupler segment, which spans a second portion of the circumference of the annular coupler. In selected aspects, the first and second portions do not overlap one another along the circumference. In certain aspects, the first and second coupler segments each span about fifty percent of the circumference of the annular coupler. Thus, each coupler segment may make up roughly half of the annular coupler.

Description:
BACKGROUND 
     1. Field of the Invention 
     This invention relates to downhole drilling, and more particularly to apparatus and methods for transmitting data along a downhole drill string. 
     2. Description of the Related Art 
     For half a century, the oil and gas industry has sought to develop downhole telemetry systems that enable high-definition formation evaluation and borehole navigation while drilling in real time. The ability to transmit large amounts of sub-surface data to the surface has the potential to significantly decrease drilling costs by enabling operators to more accurately direct the drill string to hydrocarbon deposits. Such information may also improve safety and reduce the environmental impacts of drilling. This technology may also be desirable to take advantage of numerous advances in the design of tools and techniques for oil and gas exploration, and may be used to provide real-time access to data such as temperature, pressure, inclination, salinity, and the like, while drilling. 
     In order to transmit data at high speeds along a drill string, various approaches have been attempted or suggested. One approach that is currently showing promise is to incorporate a “network” of data transmission cable and other communication equipment into the drill string. Due to the length of drill strings, which may exceed 20,000 feet, such a network may require placing network “nodes” at selected intervals along the drill string. These nodes may act as repeaters to amplify the data signal and provide points of data collection along the drill string. Communication elements, such as magnetic couplers, may be incorporated into the ends of downhole tools to transmit data across the tool joints. Transmission lines, such as electrical cables, may be incorporated into the downhole tools to transmit data therealong. 
     Unfortunately, unlike conventional above-ground networks, a downhole network is constrained by the physical limitations of the downhole drill string. In particular, a downhole drill string is a linear structure, making it very difficult to build redundancy (and thereby reliability) into the downhole network. As a result, any break or malfunction in the data transmission path along the drill string may cause communication to be lost between the surface and downhole components. Because the drill string may include many hundreds of downhole components (e.g., sections of drill pipe, drill collar, bottom-hole assembly components, etc.), a single break or malfunction in any downhole component can break the communication path and cause the network to lose much if not all of its functionality. 
     In view of the foregoing, what are needed are apparatus and methods to provide multiple redundant paths of communication in a downhole network. Such apparatus and methods may be used to significantly improve the reliability of downhole communication networks. 
     SUMMARY 
     The invention has been developed in response to the present state of the art and, in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available downhole networks. Accordingly, the invention has been developed to provide systems and methods to build redundancy into downhole networks. The features and advantages of the invention will become more fully apparent from the following description and appended claims, or may be learned by practice of the invention as set forth hereinafter. 
     In one aspect of the invention, an annular coupler for transmitting data across a tool joint may include a first coupler segment spanning a first portion of the circumference of the annular coupler. The annular coupler may further include a second coupler segment, electrically insulated from the first coupler segment, which spans a second portion of the circumference of the annular coupler. In selected aspects, the first and second portions do not overlap one another along the circumference. In certain aspects, the first and second coupler segments each span about fifty percent of the circumference of the annular coupler. Thus, each coupler segment may make up roughly half of the annular coupler. 
     In another aspect, a downhole tool in accordance with the invention may include an annular coupler installed in an end thereof. The annular coupler may include a first coupler segment spanning a first portion of the circumference of the annular coupler and a second coupler segment, electrically insulated from the first coupler segment, spanning a second portion of the circumference of the annular coupler. The first coupler segment may be coupled to a first transmission line to transmit data along the downhole tool. The second coupler segment may be coupled to a second transmission line to transmit data along the downhole tool. 
     In yet another aspect of the invention, a method for transmitting data across a tool joint may include installing an annular coupler in one of a primary and secondary shoulder of a downhole tool. Installing the annular coupler may include installing a first coupler segment in the primary or secondary shoulder that spans a first portion of the circumference of the annular coupler. Installing the annular coupler may also include installing a second coupler segment in the primary or secondary shoulder that spans a second portion of the circumference of the annular coupler. The first coupler segment may be electrically isolated from the second coupler segment. In selected aspects, the first coupler segment makes up about fifty percent of the circumference of the annular coupler and the second coupler segment makes up about the other fifty percent of the circumference of the annular coupler. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific aspects illustrated in the appended drawings. Understanding that these drawings depict only typical aspects of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through use of the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional perspective view showing two transmission lines and a split-coil annular coupler incorporated into the pin end of a downhole tool; 
         FIG. 2  is a perspective view of multiple annular couplers connected by transmission lines; 
         FIG. 3  is perspective view of one aspect of a split-coil annular coupler in accordance with the invention; 
         FIG. 4  is a perspective cutaway view of a split-coil annular coupler installed in a mating surface of a downhole tool; 
         FIG. 5  is a perspective cutaway view of the split-coil annular coupler of  FIG. 4 ; 
         FIG. 6  is a schematic view showing coupler segments rotationally aligned with one another; and 
         FIG. 7  is a schematic view showing coupler segments rotationally misaligned with one another. 
     
    
    
     DETAILED DESCRIPTION 
     It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of aspects of apparatus and methods of the present invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of various selected aspects of the invention. 
     The illustrated aspects of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. Those of ordinary skill in the art will, of course, appreciate that various modifications to the apparatus and methods described herein may be easily made without departing from the essential characteristics of the invention, as described in connection with the Figures. Thus, the following description of the Figures is intended only by way of example, and simply illustrates certain selected aspects consistent with the invention as claimed herein. 
       FIG. 1  shows a pair of transmission lines  102   a ,  102   b  and a split-coil annular coupler  104  incorporated into the pin end  108  of a downhole tool  100 . In the illustrated aspect, the downhole tool  100  is a section of drill pipe  100 . However, the downhole tool  100  may also include other tubular components such as heavyweight drill pipe, drill collars, crossovers, mud motors, stabilizers, hole openers, sub-assemblies, under-reamers, drilling jars, drilling shock absorbers, network links, downhole measurement tools, or other downhole tools known to those of skill in the art. 
     The transmission lines  102   a ,  102   b  and annular coupler  104  provide multiple redundant paths of communication along the downhole tool  100 . Consequently, if communication is lost or interrupted on one transmission line  102   a , the other transmission line  102   b  may still transmit data along the downhole tool  100 . Such a configuration may be used to provide multiple paths of communication in a downhole network, one example of which is disclosed in U.S. Pat. No. 7,041,908 to Hall et al. and entitled “Data Transmission System for a Downhole Component,” which is herein incorporated by reference in its entirety. 
     In the illustrated aspect of the invention, the annular coupler  104  is an inductive coupler  104  configured to transmit data across a tool joint as a magnetic signal. Two magnetically coupled annular couplers  104  (as would occur with two annular couplers  104  communicating across the tool joint) create a “transformer,” in this case an RF signal transformer. However, in other aspects, the annular coupler  104  may use other methods for transmitting data across the tool joint. For example, the annular coupler  104  may be an acoustic coupler, a fiber optic coupler, or an electrical coupler for communicating or transmitting a signal (i.e., an acoustic, optical, or electrical signal) across the tool joint. 
     In the illustrated aspect, the pin end  108  of the downhole tool  100  is shown. In this example, the pin end  108  is a double-shouldered design, which has been found to be particularly suitable for implementing an annular coupler  104  in accordance with the invention. One example of a double-shouldered downhole tool is described in U.S. Pat. No. 5,908,212 to Smith et al. and entitled “Ultra High Torque Double Shoulder Tool Joint.” Nevertheless, the annular coupler  104  is not limited to double-shouldered tool joints, but may be incorporated into tool joints having a wide variety of different configurations. 
     As shown, the annular coupler  104  is installed in a groove or recess formed in the secondary shoulder  106  of the pin end  108  of the downhole tool  100 . In other aspects, the annular coupler  104  may be installed in a primary shoulder or other mating surface of the downhole tool  100 . A corresponding annular coupler (not shown) may be installed in the box end of the downhole tool  100 . In selected aspects, the transmission lines  102   a ,  102   b  may be routed through holes (e.g., gun-drilled holes) formed in the pin end and box end respectively, since the wall thickness is these areas is typically greater. Where the wall thickness is thinner, such as along the length of the downhole tool  100  between the pin end and box end, the transmission lines  102   a ,  102   b  may be routed through the central bore  110  of the downhole tool  100 . In selected aspects, the transmission lines  102   a ,  102   b  may be held under tension to minimize movement of the transmission lines  102   a ,  102   b  within the central bore  110 , and to keep the transmission lines  102   a ,  102   b  against the wall of the central bore  110 . 
     Referring to  FIG. 2 , a perspective view of multiple split-coil annular couplers  104   a - d,  connected by transmission lines  102   a - d , is illustrated. A first set of annular couplers  104   a ,  104   b  and transmission lines  102   a ,  102   b  may be installed in a first downhole tool, and a second set of annular couplers  104   c ,  104   d  and transmission lines  102   c ,  102   d  may be installed in a second downhole tool physically coupled to (e.g., threaded into) the first downhole tool. A pair of annular couplers  104   b ,  104   c  may communicate with one another across the tool joint. 
     As shown, a pair of transmission lines  102  may communicate with each annular coupler  104 . Each transmission line  102  may communicate with a different electrically-isolated coupler segment  200 , as will be explained in more detail hereafter. For example, a first transmission line  102   c  may communicate with a first coupler segment  200   a , and a second transmission line  102   d  (which is electrically isolated from the first transmission line  102   c ) may communicate with a second coupler segment  200   b  (which is electrically isolated from the first coupler segment  200   a ). In the event one of the couplers segments  200   a  shorts out or ceases to function for some reason, the other coupler segment  200   b  and transmission line  102   d  may continue to function. In this way, redundancy may be built into the downhole network by providing multiple paths of communication through each downhole tool. 
     One significant advantage of the “split-coil” couplers  104  shown in  FIG. 2  is that if a first coupler segment  200   a  ceases to function, it is not likely to cause the second coupler segment  200   b  to also cease to function. For example, if the coupler segments  200   a ,  200   b  were in close proximity to one another (such as two overlapping segments), a failure of one coupler segment  200   a  could also cause the failure of the other  200   b . For example, a scrap of metal, pebble, or other material that interferes with and shorts out a first coupler segment  200   a  would also likely short out the other coupler segment  200   b  since it is in close physical proximity thereto. By dividing the annular coupler  104  into segments  200   a ,  200   b , the segments  200   a ,  200   b  may be physically and electrically separated from one another to reduce the chance that a failure of one will cause the failure of the other. 
     Referring to  FIG. 3 , one aspect of a split-coil annular coupler  104  in accordance with the invention is illustrated. In this aspect, the annular coupler  104  is divided into a pair of coupler segments  200   a ,  200   b , although more coupler segments (and associated transmission lines) are also possible. In this aspect, each coupler segment  200   a ,  200   b  makes up about fifty percent of the circumference of the annular coupler  104 . Other ratios are possible and within the scope of the invention. 
     In the illustrated aspect, each coupler segment  200   a ,  200   b  includes half of a conductive coil  300   a ,  300   b  (i.e., together forming a “split coil”). Each coil  300   a ,  300   b  is partially surrounded by magnetically-conductive, electrically-insulating (MCEI) elements, which may be inserted into an annular housing  304 . The conductive coils  300   a ,  300   b  may be coupled to conductive straight portions  302   a ,  302   b , which may be electrically coupled (by soldering, contact, or other means) to the transmission lines  102 . The other ends of the coils  300   a ,  300   b  maybe grounded. For example, an end  306  may be grounded by way of soldering, welding, or direct contact with the annular housing  304  (this makes a ½ turn coil that is a complete circuit). The annular housing  304  may be grounded by way of direct contact with the tool  100 . In certain aspects, the coils  300   a ,  300   b  and straight portions  302   a ,  302   b  may be pieces of wire that are bent or formed into the illustrated shapes. In certain aspects, the entire annular coupler  104  is preassembled before being installed in the downhole tool  100 . 
     Referring to  FIG. 4 , a perspective, cross-sectional view of one aspect of a split-coil annular coupler  104  in accordance with the invention is illustrated. In selected aspects, the annular coupler  104  may include an annular housing  304  forming a trough. MCEI elements  400  may be placed within the trough. In certain aspects, the MCEI elements  400  are fabricated from a ferrite material or other material with similar electrical and magnetic properties. Similarly, the MCEI elements  400  may be formed in a U-shape that is sized and shaped to fit within the annular housing  304 . The annular housing  304  may provide a durable frame in which to house the relatively fragile MCEI elements  400 . The conductive coil  300  may be provided within the U-shaped MCEI elements  400  to carry electrical current. In selected aspects, the conductive coil  300  is coated with an electrically insulating material  402 . For example, the conductive coil  300  may be made of copper or silver-plated copper-clad steel, which may be insulated with varnish, enamel, or a polymer. In other aspects, the coil  300  is insulated with a tough, flexible polymer, such as high density polyethylene or polymerized tetrafluoroethane (PTFE). 
     As current flows through the coil  300 , a magnetic flux or field may be created around the coil  300 . The U-shaped MCEI elements  400  may contain the magnetic flux created by the coil  300  and prevent energy leakage into surrounding materials. The U-shape of the MCEI elements  400  may also serve to transfer magnetic current to a similarly shaped MCEI element  400  in an adjacent annular coupler  104 . Since materials such as ferrites may be quite brittle, the U-shaped MCEI elements  400  may be provided in segments  404   a ,  404   b  to prevent cracking or breaking that might occur using a monolithic piece of ferrite. In selected aspects, these segments  404   a ,  404   b  may be held together using a resilient material, such as an epoxy, a natural rubber, polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), a fiberglass or carbon fiber composite, a polyurethane, or the like. 
     As was previously discussed, an annular recess  406  may be provided in a mating surface  408  of the downhole tool  100 , such as in the secondary shoulder  408  of the downhole tool  100 . The recess  406  may be positioned so as to lie substantially equidistant between the inner and outer diameter of the secondary shoulder or face. The annular coupler  104  may be inserted into and retained within the recess  406 . In selected aspects, the recess  406  may include a locking mechanism to enable the annular housing  304  to be retained within the recess  406 . For example, in one aspect, a locking mechanism may include a groove  410  or recess  410  formed within the larger recess  406 . A corresponding shoulder  412  may be formed along the annular housing  304 . This shoulder  412  may engage the groove  410 , thereby retaining the annular coupler  104  within the recess  406 . 
     In order to close any gaps between annular couplers  104  in the pin end and box end of downhole tools  100  making up a tool joint, an annular coupler  104  may be biased with respect to the mating surface  408 . That is, the annular coupler  104  may be urged in a direction  414  with respect to the mating surface  408 . In selected aspects, angled surfaces  416 ,  418  of the recess  406  and the annular housing  304 , along with the diameters of the annular housing  304  and the recess  406  may provide a “spring force” in the direction  414 . This may be accomplished may making the diameter of the annular housing  304  slightly smaller than the diameter of the recess  406  and then pressing the annular housing  304  into the recess  406  until the shoulder  412  snaps into the groove  410 . The top surface of the annular coupler  104  may slit slightly above the mating surface  408 , but may travel downward into the recess  406  upon contacting a corresponding annular coupler  104  of an adjacent downhole tool  100 . The spring force may keep the annular couplers  104  in firm contact with one another, improving their ability to transmit a signal across the tool joint. 
     Referring to  FIG. 5 , another cutaway view of the split-coil annular coupler  104  of  FIG. 4  is illustrated. As shown, the annular coupler  104  includes an annular housing  304 , forming a trough, with multiple MCEI elements  400  residing in the trough. The MCEI elements  400  are U-shaped with a size and shape to fit within the annular housing  304 . A conductive coil  300  is routed through the U-shaped MCEI elements  400 . An electrically insulating material  402  is used to coat the conductive coil  300 . A shoulder  412  is formed along the inside diameter of the annular housing  304  to enable the shoulder  412  to engage a corresponding groove  410  in the annular recess of the downhole tool  100 . 
     Referring to  FIGS. 6 and 7 , one advantage of the present invention is that communication may be maintained regardless of the “clocking” of the annular couplers  104 . For example, referring to  FIG. 6 , where the annular couplers  104   a ,  104   b  are substantially aligned, a coupler segment  200   a  of the annular coupler  104   a  will be aligned with the coupler segment  200   c  of the annular coupler  104   b . Similarly, a coupler segment  200   b  of the annular coupler  104   a  will be aligned with the coupler segment  200   d  of the annular coupler  104   b . If one of the coupler segments  200   a ,  200   c  loses functionality, communication may nevertheless be maintained between the other coupler segments  200   b ,  200   d . Similarly, if one of the coupler segment  200   b ,  200   d  loses functionality, communication may be maintained between the coupler segments  200   a ,  200   c . In this scenario, most if not all of the signal power from the coupler segment  200   a  will be transmitted to the coupler segment  200   c , and most if not all of the signal power from the coupler segment  200   b  will be transmitted to the coupler segment  200   d.    
     On the other hand, where the annular couplers  104   a ,  104   b  are misaligned, the annular couplers  104   a ,  104   b  may still maintain communication. For example, referring to  FIG. 7 , consider a case where a coupler segment  200   a  of the annular coupler  104   a  is misaligned with the coupler segment  200   c  of the annular coupler  104   b , and a coupler segment  200   b  of the annular coupler  104   a  is misaligned with the coupler segment  200   d  of the annular coupler  104   b . If a coupler segment  200   a  loses functionality, communication may nevertheless be maintained between the coupler segments  200   b ,  200   d . Communication may also exist between the coupler segment  200   b  and the coupler segment  200   a  of the annular coupler  104   b . The difference between this scenario and that illustrated in  FIG. 6  is that power transmitted from the coupler segment  200   b  will be split in some proportion between the coupler segments  200   a ,  200   d . Thus, the annular couplers  104   a ,  104   b  may maintain communication regardless of the “clocking” between the annular couplers  104   a ,  104   b . In either case ( FIG. 6  or  7 ), a drop in signal power (that would not prevent the network from functioning correctly) could be used as a warning that a tool joint has a failure in one of the two communication paths. 
     The present invention may be embodied in other specific forms without departing from its essential characteristics. The described aspects are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.