Abstract:
An electrical contact system for transmitting information across tool joints while minimizing signal reflections that occur at the tool joints includes a first electrical contact comprising an annular resilient material. An annular conductor is embedded within the annular resilient material and has a surface exposed from the annular resilient material. A second electrical contact is provided that is substantially equal to the first electrical contact. Likewise, the second electrical contact has an annular resilient material and an annular conductor. The two electrical contacts configured to contact one another such that the annular conductors of each come into physical contact. The annular resilient materials of each electrical contact each have dielectric characteristics and dimensions that are adjusted to provide desired impedance to the electrical contacts.

Description:
FEDERAL RESEARCH STATEMENT  
       [[0001]]     This invention was made with government support under Contract No. DE-FC26-97F343656 awarded by the U.S. Department of Energy. The government has certain rights in the invention. 
     
    
     BACKGROUND OF INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to oil and gas drilling, and more particularly to apparatus and methods for reliably transmitting information between downhole drilling components.  
         [0004]     2. Background of the Invention  
         [0005]     In the downhole drilling industry, MWD and LWD tools are used to take measurements and gather information concerning downhole geological formations, status of downhole tools, and other conditions located downhole. Such data is useful to drill operators, geologists, engineers, and other personnel located at the surface. This data may be used to adjust drilling parameters, such as drilling direction, penetration speed, and the like, to effectively tap into an oil or gas bearing reservoir. Data may be gathered at various points along the drill string, such as from a bottom hole assembly or from sensors distributed along the drill string.  
         [0006]     Nevertheless, data gathering and analysis represent only certain aspects of the overall process. Once gathered, apparatus and methods are needed to rapidly and reliably transmit the data to the earth&#39;s surface. Traditionally, technologies such as mud pulse telemetry have been used to transmit data to the surface. However, most traditional methods are limited to very slow data rates and are inadequate for transmitting large quantities of data at high speeds.  
         [0007]     In order to overcome these limitations, various efforts have been made to transmit data along electrical and other types of cable integrated directly into drill string components, such as sections of drill pipe. In such systems, electrical contacts or other transmission elements are used to transmit data across tool joints or connection points in the drill string. Nevertheless, many of these efforts have been largely abandoned or frustrated due to unreliability and complexity.  
         [0008]     For example, drill strings may include hundreds of sections of drill pipe and other downhole tools connected in series. In order to reach the surface, data must be transmitted reliably across each tool joint. A single faulty connection may break the link between downhole sensors and the surface. Also, because of the inherent linear structure of a drill string, it is very difficult to build redundancy into the system.  
         [0009]     The unreliability of various known contact systems is due to several factors. First, since the tool joints are typically screwed together, each of the tools rotate with respect to one another. This causes the contacts to rotate with respect to one another, causing wear, damage, and possible misalignment. In addition, as the tool joints are threaded together, mating surfaces of the downhole tools, such as the primary and secondary shoulders, come into contact. Since downhole tools are not typically manufactured with precise tolerances that may be required by electrical contacts, this may cause inconsistent contact between the contacts.  
         [0010]     Moreover, the treatment and handling of drill string components is often harsh. For example, as sections of drill pipe or other tools are connected together, ends of the drill pipe may strike or contact other objects. Thus, delicate contacts or transmission elements located at the tool ends can be easily damaged. In addition, substances such as drilling fluids, mud, sand, dirt, rocks, lubricants, or other substances may be present at or between the tool joints. This may degrade connectivity at the tools joints. Moreover, the transmission elements may be subjected to these conditions each time downhole tools are connected and disconnected.  
         [0011]     Thus, what are needed are reliable contacts for transmitting data across tool joints that are capable of overcoming the previously mentioned challenges.  
         [0012]     What are further needed are reliable contacts that are resistant to wear and tear encountered in a downhole environment.  
         [0013]     What are further needed are reliable contacts that, even when damaged, still provide reliable connectivity.  
         [0014]     What are further needed are apparatus and method to adjust the impedance of the contacts to minimize signal reflections at the tool joints.  
       SUMMARY OF INVENTION  
       [0015]     In view of the foregoing, it is a primary object of the present invention to provide apparatus and methods for reliably transmitting information between downhole tools in a drill string. It is a further object of the invention to provide robust electrical connections that may withstand the rigors of a downhole environment. It is yet another object of the invention to provide apparatus and methods to reduce signal reflections that may occur at the tool joints.  
         [0016]     Consistent with the foregoing objects, and in accordance with the invention as embodied and broadly described herein, an electrical contact system for transmitting information across tool joints, while minimizing signal reflections that occur at the tool joints, is disclosed in one embodiment of the invention as including a first electrical contact comprised of an annular resilient material. An annular conductor is embedded within the annular resilient material and has a surface exposed from the annular resilient material.  
         [0017]     A second electrical contact is provided that is substantially equal to the first electrical contact. Likewise, the second electrical contact has an annular resilient material and an annular conductor. The two electrical contacts configured to contact one another such that the annular conductors of each come into physical contact. The annular resilient materials of each electrical contact each have dielectric characteristics and dimensions that are adjusted to provide desired impedance to the electrical contacts.  
         [0018]     In selected embodiments, the first and second electrical contacts further include first and second annular housings, respectively, to accommodate the annular resilient materials, and the annular conductors, respectively. In certain embodiments, the electrical contact system includes one or several biasing member to urge each of the electrical contacts together. For example, the biasing member may be a spring, an elastomeric material, an elastomeric-like material, a sponge, a sponge-like material, or the like. In other embodiments, one or both of the annular housings are sprung with respect to corresponding mating surfaces of downhole tool in which they are mounted. This may provide a biasing effect to one or both of the electrical contacts.  
         [0019]     In selected embodiments, the first and second electrical contacts are configured such that pressure encountered in a downhole environment presses them more firmly together. In other embodiments, one or both of the electrical contacts are configured to “orbit” with respect to a mating surface of a downhole tool. By “orbiting,” it is meant that the electrical contacts may pivot along multiple axes to provide improved contact.  
         [0020]     In certain embodiments, the annular resilient materials are constructed of a material selected to flow into voids that may or may not be present within the electrical contacts. In selected embodiments, the annular resilient material may be constructed of a material such as silicone, Vamac, polysulfide, Neoprene, Hypalon, butyl, Teflon, millable or cast polyurethane, rubber, fluorosilicone, epichlorohydrin, nitrile, styrene butadiene, Kalrez, fluorocarbon, Chemraz, Aflas, other polymers, and the like. To provide strength, durability, or other characteristics, modifiers such as Kevlar, fibers, graphite, or like materials, may be added to the annular resilient material.  
         [0021]     In selected embodiments, a cable is electrically connected to one or both of the electrical contracts, and the impedance of one or both of the electrical contacts is adjusted to match the impedance of the cable. In certain embodiments, the cable is a coaxial cable. In other embodiments, multiple annular conductors may be embedded in the annular resilient material to provide multiple connections.  
         [0022]     In another aspect of the present invention, a method for transmitting information across tool joints in a drill string, while minimizing signal reflections occurring at the tool joints, may include providing a first electrical contact comprised of an annular resilient material, and an annular conductor embedded within the first annular resilient material. The annular conductor has a surface exposed from the annular resilient material. The method may further include providing a corresponding electrical contact substantially equal to the first electrical contact. The corresponding electrical contact also includes an annular resilient material and a second annular conductor. The method further includes adjusting the dielectric characteristics, the dimensions, or both of the annular resilient materials to provide desired impedance to the electrical contacts.  
         [0023]     In selected embodiments, the method may further include providing annular housings to the electrical contacts, respectively, to accommodate the annular resilient materials, and the annular conductors. In certain embodiments, a method in accordance with the invention includes urging the electrical contacts together. Likewise, adjusting may include adjusting the impedance to match the impedance of a cable electrically connected to at least one of the first and second electrical contracts. In certain embodiments, the cable is a coaxial cable. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0024]     The foregoing and other features of the present invention will become more fully apparent from the following description, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only typical embodiments in accordance with the invention and are, therefore, not to be considered limiting of its scope, the invention will be described with additional specificity and detail through use of the accompanying drawings.  
         [0025]      FIG. 1  is a perspective view illustrating one embodiment of an electrical contact assembly in accordance with the invention.  
         [0026]      FIG. 2  is a perspective cross-sectional view of the electrical contact assembly illustrated in  FIG. 1 .  
         [0027]      FIG. 3  is a cross-sectional view illustrating one embodiment of the internal components of the electrical contract assembly of  FIG. 1 ;  
         [0028]      FIG. 4  is a cross-sectional view illustrating one embodiment of a connection point between the annular contact and a conductive cable.  
         [0029]      FIGS. 5A-5C  are various cross-sectional views illustrating the mating relationship between two electrical contact assemblies in accordance with the invention.  
         [0030]      FIGS. 6A-6C  are various cross-sectional views illustrating one embodiment of the mating relationship between two electrical contact assemblies when a void or damaged area exists in one of the assemblies.  
         [0031]      FIG. 7  is a cross-sectional view illustrating one embodiment of various gripping features that may be integrated into the annular contact.  
         [0032]      FIG. 8  is a cross-sectional view illustrating one embodiment of an annular contact that resembles the core of a traditional coaxial cable.  
         [0033]      FIG. 9  is a perspective view illustrating one embodiment of an electrical contact assembly in accordance with the invention having multiple annular contacts.  
         [0034]      FIG. 10  is a cross-sectional view of the electrical contact assembly illustrated in  FIG. 9 . 
     
    
     DETAILED DESCRIPTION  
       [0035]     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 embodiments 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 embodiments of the invention.  
         [0036]     The illustrated embodiments 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 easily be 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 embodiments consistent with the invention as claimed herein.  
         [0037]     Referring to  FIG. 1 , a contact assembly  10  in accordance with the invention may be characterized by a substantially annular shape. This annular shape may enable the contact assembly  10  to be installed in the box end or pin end of a downhole tool (not shown). For example, the contact assembly  10  may be installed in an annular recess milled into the primary or secondary shoulder of a downhole tool (not shown).  
         [0038]     In selected embodiments, a contact assembly  10  may include an annular housing  12  and a resilient material  16  located within the housing  12 . An annular contact  14  may be embedded into the resilient material and may have a surface exposed from the resilient material  16 . The resilient material  16  may serve to insulate the annular conductor  14  from the housing  12  as well as perform other functions described in this specification. In selected embodiments, a cable  18  may include a conductor connected to the annular contact  14 . In certain embodiments, the contact assembly  10  may include an alignment and retention member  20  that may fit within a corresponding recess milled or formed into the downhole tool. The retention member  20  may be used to retain a desired tension in the cable  18 .  
         [0039]     Referring to  FIG. 2 , a cross-sectional view of the contact assembly  10  of  FIG. 1  is illustrated. As is illustrated, a housing  12  may be used to accommodate a resilient material  16  and a conductor  14  embedded within the resilient material. In certain embodiments, the conductor  16  may have a substantially rectangular or elongated cross-section to provide substantial surface area between the conductor  14  and the resilient material  16  to provide sufficient adhesion therebetween. Nevertheless, the conductor  14  may have any of numerous cross-sectional shapes, as desired. In selected embodiments, the resilient material  16  may have a rounded or curved contour  22  such that the resilient material  16  and conductor  14  reside above the housing  12 .  
         [0040]     Referring to  FIG. 3 , an enlarged cross-sectional view of the contact assembly  10  is illustrated. As shown, the housing  12  may include an angled surface  24 . The contact assembly  10  may sit in a recess  23  milled or formed in the primary or secondary shoulder  27  of a downhole tool  27 . The recess  23  may include a corresponding angled surface  25 . By manufacturing the housing  12  such that it has a radius slightly smaller than the radius of the recess  23 , the angled surfaces  24 ,  25  may exert force against one another such that the contact assembly  10  is urged in a direction  29 . That is, the angled surfaces  24 ,  25  may create a spring-like force urging the housing  12  in the direction  29 . Likewise, when a force  33  is exerted on the contact assembly  10 , the contact assembly  10  may be urged down into the recess  23 . In selected embodiments, the contact assembly  10  may “orbit” with respect to a mating surface  27 . That is, due to the biasing effect of the surfaces  24 ,  25 , the annular contact  10  may move with respect to the mating surface  27  similar to a universal joint. This may provide better and more consistent contact between contact assemblies  10 .  
         [0041]     As illustrated, the housing  12  may include a shoulder  26  that may engage a corresponding shoulder milled or formed into the recess  23 . This may enable the contact assembly  10  to be pressed into the recess  23 . Once inserted, the shoulder  26  may prevent the contact assembly  10  from exiting the recess  23 . Likewise, the housing  12  may optionally include one or several retaining shoulder  28   a ,  28   b  to help retain the resilient material  16  within the housing  12 .  
         [0042]     As was previously mentioned with respect to  FIG. 1 , the conductor  14  may be connected to a cable  18 . In selected embodiments, the cable  18  may be a coaxial cable  18 . As is typical of most coaxial cables  18 , or other cables  18  for that matter, each usually has a rated impedance. In coaxial cable  18 , the impedance is usually a function of the diameter of the cable  18 , the diameter of the core conductor, and the diameter and dielectric constant of a dielectric material surrounding the core conductor. In order to minimize signal reflections, it is important to match as accurately as possible the impedance of the contact assembly  10  to the impedance of the coaxial or other cable  18 .  
         [0043]     Thus, in selected embodiments, the impedance of the contact assembly  10  may be adjusted to match a particular coaxial cable  18  being used. In certain embodiments, the contact assembly  10  may more or less resemble coaxial cable. For example, the conductor  14  may be analogous to the core conduct of coaxial cable, the housing  12  may be analogous to the coaxial shield, and the resilient material  16  may be analogous to the dielectric material within the coaxial cable  18 . By adjusting the dimensions  30   a ,  30   b ,  32  of the resilient material  16 , and the dielectric properties of the resilient material  16 , the impedance of the contact assembly  10  may be adjusted to provide a desired impedance. Thus, signal reflections occurring at the contact assemblies  10  may be minimized as much as possible.  
         [0044]     The resilient material  16  may be constructed of any suitable material capable of withstanding a downhole environment. For example, in certain embodiments, the resilient material  16  may be constructed of a material such as silicone, Vamac, polysulfide, Neoprene, Hypalon, butyl, Teflon, millable or cast polyurethane, rubber, fluorosilicone, epichlorohydrin, nitrile, styrene butadiene, Kalrez, fluorocarbon, Chemraz, Aflas, other polymers, and the like. To provide strength, durability, or other characteristics, modifiers such as Kevlar, fibers, graphite, or like materials, may be added to the annular resilient materials  16 .  
         [0045]     Referring to  FIG. 4 , as was previously mentioned with respect to  FIG. 1 , the annular contact  14  might be connected to a cable  18 , such as a coaxial cable  18 . As is illustrated, a conductor  34  may extend through the housing  12  and the resilient material  16  to connect to the annular conductor  14 . The connection may be made by soldering, welding, or any other suitable method to produce a strong, conductive bond. As illustrated, a sheath  36 , such as an insulator or coaxial sheathing, may protect and insulate the conductor  34 .  
         [0046]     Referring to  FIGS. 5A-5C , two contact assemblies  10   a ,  10   b  are illustrated transitioning from a separated to a connected state. In  FIG. 5A , when the contact assemblies  10   a ,  10   b  are separated, the resilient material  16   a ,  16   b  may have a rounded or protruding surface  22   a ,  22   b . In selected embodiments, the resilient material  16   a ,  16   b  may protrude out more than the contacts  14   a ,  14   b  such that the surfaces  22   a ,  22   b  meet before the contacts  14   a ,  14   b . This may provide a seal to isolate the contacts  14   a ,  14   b  from the surrounding environment. Since the contacts  14   a ,  14   b  may electrically arc when they near each other, isolating the contacts  14   a ,  14   b  may help prevent this arcing from igniting gases or other flammable substances that may be present in a downhole drilling environment. Nevertheless, in other embodiments, the contacts  14   a ,  14   b  may actually be flush with or protrude out farther than the resilient materials  16   a ,  16   b.    
         [0047]     Referring to  FIG. 5B , as the contact assemblies  10   a ,  10   b  near one another, the contacts  14   a ,  14   b  may meet. As this occurs, the resilient materials  16   a ,  16   b  may begin to compress into the housings  12   a ,  12   b . Due to their resiliency, the resilient materials  16   a ,  16   b  may provide a spring like force urging the contacts  14   a ,  14   b  together.  
         [0048]     Referring to  FIG. 5C , in selected embodiments, as the resilient materials  16   a ,  16   b  continue to compress into the housings  12   a ,  12   b , they may flatten to form more planar surfaces  40   a ,  40   b . Likewise, the increased compression keeps the contacts  14   a ,  14   b  more firmly pressed together. In selected embodiments, the resilient materials  16   a  ,  16   b  may actually protrude or be squeezed slightly from the housings  12   a ,  12   b  at a point  44 . In other embodiments, even when the contact assemblies  10   a ,  10   b  are fully pressed together, a gap  42  may still be present between the housings  12   a ,  12   b . Thus, the resilient materials  16   a ,  16   b  may continue to exert force on the contacts  14   a ,  14   b  without having this energy absorbed by contact of the housings  12   a ,  12   b.    
         [0049]     In selected embodiments, three “energizing” elements may contribute to keep the contacts  14   a ,  14   b  firmly pressed together. First, as was previously mentioned with respect to  FIG. 3 , the housings  12   a ,  12   b  may be spring-loaded with respect to their respective recesses  23 , thereby urging the contact assemblies  10   a ,  10   b  together. Second, the resilient materials  16   a ,  16   b  may provide a spring-like force urging the contacts  14   a ,  14   b  together. Lastly, high-pressure levels  45  often present downhole may exert a force on the housings  12   a ,  12   b , keeping the contact assemblies  10   a ,  10   b  firmly pressed together. Any or all of these “energizing” forces may be used to provide more reliable contact between the contacts  14   a ,  14   b.    
         [0050]     Referring to  FIGS. 6A-6C , two damaged or asymmetrical contact assemblies  10   a ,  10   b  are illustrated transitioning from a separated to a connected state. As was previously mentioned, downhole tools may be subjected to hostile environments downhole. Moreover, this harsh treatment may also occur at the surface as tool sections are connected and disconnected. This provides ample opportunity for the contact assemblies to be damaged, worn, and the like. Since the reliability of contact assemblies is very important, their ability to withstand damage or wear is a desired attribute.  
         [0051]     Referring to  FIG. 6A , in certain instances, damage or other events may create a void  46  or damaged area  46  in the resilient material  16   b . For example, when the pin and box end of downhole tools are threaded together, the contact assemblies  10   a ,  10   b  may rub against one another. Dirt, rocks, or other substances may become interposed between the surfaces of the contact assemblies  10 . This may cause abrasion or wear that may remove a portion of the resilient material  16   b , thereby creating the void  46 . Other conditions, such as striking the ends of drill tools, downhole pressure, and the like, may also cause damage to the contact assemblies  10   a ,  10   b.    
         [0052]     Referring to  FIG. 6B , as the contact assemblies  10   a ,  10   b  come together, the void may create an undesirable gap  47  between the resilient materials  16   a ,  16   b . This may cause undesired exposure of the contacts  14   a ,  14   b , possibly causing shorting, corrosion, arcing, or the like.  
         [0053]     Referring to  FIG. 6C , nevertheless, by proper selection of resilient materials  16   a ,  16   b  such as those listed with respect to  FIG. 3 , the contact assemblies  10   a ,  10   b  may compensate for voids or damage that may be present in the resilient material  16   b . For example, when the contact assemblies  10   a ,  10   b  are pressed together, the resilient material  16   a  from one contact assembly  10   a  may flow into the void  46  of the other resilient material  16   b . Thus, even when damage is present, the resilient materials  16   a ,  16   b  may conform to one another, provide a spring-like bias to the contacts  14   a ,  14   b , and seal out potential contaminants.  
         [0054]     Referring to  FIG. 7 , in selected embodiments, the contact  14  may be shaped or textured to include gripping features  48 . For example, the gripping features  48  may be barbs, or may simply be surface textures created by sanding or otherwise roughening the surface of the contact  14 . Since, the resilient material  16  may be compressed when contacting another contact assembly  10 , the contact  14  may tend to separate from the resilient material  16 . Thus, the gripping features  48  may provide improved adhesion between the resilient material  16  and the contact  14 . Likewise, although not illustrated, the inside of the housing  12  may be textured or have other surface features to provide improved adhesion between the resilient material  16  and the housing  12 .  
         [0055]     Referring to  FIG. 8 , in selected embodiments, the contact  14  may resemble a half cylinder or a shape similar thereto. Thus, when two contact assemblies  10  come together, the contact  14  may form a substantially cylindrical core  14 . Thus, the contact assemblies  10  may more closely resemble a typical coaxial cable having a cylindrical core. This may provide improved matching with a coaxial cable, thereby reducing signal reflections.  
         [0056]     Referring to  FIG. 9 , in other embodiments, multiple annular conductors  14   a ,  14   b  may be provided in a contact assembly  10 . For example, in selected embodiments, one conductor  14   a  may provide a downhole link, and a second conductor  14   b  may provide an uphole link. Or in other embodiments, one conductor  14   a  may be used to carry data and the other  14   b  power. In other embodiments, more than two conductors  14  may be used to carry, data, power, or a combination thereof.  
         [0057]     Referring to  FIG. 10 , a cross-sectional view of the contact assembly  10  of  FIG. 9  is illustrated. As shown, two or more conductors  14   a ,  14   b  may be embedded within the resilient material  16  and may be separated by an appropriate distance to prevent shorting or crosstalk.  
         [0058]     The present invention may be embodied in other specific forms without departing from its essence or essential characteristics. The described embodiments 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 within the meaning and range of equivalency of the claims are to be embraced within their scope.