Abstract:
A transmission line assembly for transmitting information along a downhole tool comprising a pin end, a box end, and a central bore traveling between the pin end and the box end, is disclosed in one embodiment of the invention as including a protective conduit. A transmission line is routed through the protective conduit. The protective conduit is routed through the central bore and the ends of the protective conduit are routed through channels formed in the pin end and box end of the downhole tool. The protective conduit is elastically forced into a spiral or other non-linear path along the interior surface of the central bore by compressing the protective conduit to a length within the downhole tool shorter than the protective conduit.

Description:
FEDERAL RESEARCH STATEMENT 
     This invention was made with government support under Contract No. DE-FC26-01NT41229 awarded by the U.S. Department of Energy. The government has certain rights in the invention. 
    
    
     BACKGROUND OF INVENTION 
     1. Field of the Invention 
     This invention relates to oil and gas drilling, and more particularly to apparatus and methods for reliably transmitting information along downhole drilling strings. 
     2. Background 
     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, gas, or other mineral 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. 
     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. 
     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. 
     For example, one challenge is effectively integrating a transmission line into a downhole tool, such as a section of tool. Due to the inherent nature of drilling, most downhole tools have an elongated cylindrical shape defining a central bore. The wall thickness surrounding the central bore is typically designed in accordance with weight, strength, and other constraints needed to operate in a downhole environment. In some cases, the wall thickness may not be sufficient to allow for direct integration of a transmission line into the wall without significantly weakening the wall. Thus, in certain instances, the transmission line may be routed through the internal bore of the downhole tool. 
     Nevertheless, routing the transmission line through the internal bore may create interference between the transmission line and drilling fluids, cements, wireline tools, or other substances or objects passing through the central bore. Moreover, in directional drilling applications, drill tools may bend slightly as a drill string deviates from a straight path. In these circumstances, the transmission line may actually deviate away from the internal surface of the central bore, thereby worsening the obstruction within the internal bore of the downhole tool. The operation of drilling fluids, cement, wireline tools, or other components may be adversely affected by interference with the transmission line or, in other instances, the transmission line itself may be damaged. 
     Thus, what are needed are apparatus and methods to route a transmission line though the central bore of a downhole tool, without interfering with drilling fluids, cement, wireline tools, or other components that may be present in the central bore. 
     What are further needed are apparatus and methods to keep a transmission line firmly pressed against the inside surface of the central bore even when the downhole tool bends or deviates from a linear path. 
     What are further needed are apparatus and methods to protect a transmission line from components or substances located or traveling through the central bore of a downhole tool. 
     SUMMARY OF INVENTION 
     In view of the foregoing, it is a primary object of the present invention to provide apparatus and methods for routing a transmission line though the central bore of a downhole tool, without interfering with drilling fluids, cement, wireline tools, or other components or substances present in the central bore. It is a further object of the invention to provide apparatus and methods to keep a transmission line firmly positioned against the inside surface of the central bore even when the downhole tool bends or deviates from a linear path. It is yet a further object of the invention to provide apparatus and methods to protect a transmission line from components or substances passing through the central bore of a downhole tool. 
     Consistent with the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a transmission line assembly for transmitting information along a downhole tool comprising a pin end, a box end, and a central bore traveling between the pin end and the box end, is disclosed in one embodiment of the invention as including a protective conduit. A transmission line is routed through the protective conduit. The protective conduit is routed through the central bore and the ends of the protective conduit are routed through channels formed in the pin end and box end of the downhole tool. The protective conduit is elastically forced into a spiral or other non-linear path along the interior surface of the central bore by compressing the protective conduit to fit within a length of the downhole tool shorter than the protective conduit. 
     In selected embodiments, the protective conduit is narrowed to provide improved contact between the protective conduit and the transmission line. In certain embodiments, this narrowing provides additional stiffness to the protective conduit, thereby keeping the conduit more firmly pressed against the internal surface of the central bore. In selected embodiments, the narrowing makes the conduit less subject to deformation in the presence of cement, wireline or logging tools, drilling fluids, or other components or substances in the central bore. 
     In certain embodiments, the protective conduit is configured to stay pressed against the inside surface of the central bore even when the downhole tool bends in directional drilling applications. The transmission line may be a coaxial cable, conductive wires, optical fibers, waveguides, or like transmission media. In selected embodiments, the ends of the protective conduit are fixed at the pin end and box end of the downhole tool to retain the protective conduit. 
     In another aspect of the present invention, a method for routing a transmission line assembly through a drill tool having a pin end, a box end, and a central bore traveling between the pin end and the box end, includes providing a protective conduit and routing a transmission line through the protective conduit. The method further includes routing the protective conduit through the central bore, and routing the ends of the protective conduit through channels formed in the pin end and box end of the downhole tool. The method further includes compelling the protective conduit to a spiral or non-linear path along the interior surface of the central bore by constraining the protective conduit to fit within a length of the drill tool shorter than the protective conduit. 
     In selected embodiments, the method includes narrowing the protective conduit to provide improved contact between the protective conduit and the transmission line. This narrowing may provide additional stiffness to the protective conduit, thereby making the protective conduit less subject to deformation in the presence of downhole cement, wireline or logging tools, drilling fluids, or other downhole tools or substances. The added stiffness may also be effective to more firmly urge the protective conduit against the interior surface of the central bore. 
     In selected embodiments, the spiral or non-linear path the conduit takes through the central bore may be effective to maintain contact between the protective conduit and the internal bore when the downhole tool bends in directional drilling applications. In certain embodiments, the transmission line may be coaxial cable, conductive wire, optical fiber, waveguides, or like transmission media. In other embodiments, a method in accordance with the invention includes fixing the ends of the protective conduit proximate the pin end and the box end of the downhole tool, respectively. 
     In another aspect of the present invention, a method for forming a transmission line assembly for routing through a drill tool having a pin end, a box end, and a central bore traveling between the pin end and the box end, includes providing a protective conduit and routing a transmission line through the protective conduit. The method further includes narrowing the protective conduit to provide improved contact between the protective conduit and the transmission line, and routing the protective conduit through the drill tool such that it spirals or takes a non-linear path along the interior surface of the central bore. The ends of the protective conduit are routed through channels formed in the pin end and box end of the downhole tool. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       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. 
         FIG. 1  is a cross-sectional view illustrating one embodiment of separation that may occur between a substantially linear transmission line and the central bore of a downhole drill tool when the drill tool is curved or bent as is customary in directional drilling applications. 
         FIG. 2  is a cross-sectional view of a non-linear or spiraled transmission line integrated into a drill tool similar to that illustrated in  FIG. 1 , wherein the transmission line maintains substantial contact with the inside surface of the central bore of the drill tool. 
         FIG. 3  is a cross-sectional view illustrating one embodiment of a linear transmission line initially inserted into the central bore of a downhole drill tool. 
         FIG. 4  is a cross-sectional view illustrating one embodiment of a linear transmission line beginning to buckle as it is elastically forced or urged into the downhole drill tool. 
         FIG. 5  is a cross-sectional view illustrating one embodiment of a linear transmission line further elastically forced or urged into the downhole drill tool such that the linear transmission line begins to coil or spiral within the central bore of the drill tool. 
         FIG. 6  is a cross-sectional view illustrating one embodiment of a linear transmission line further elastically forced or urged into the downhole drill tool such that the linear transmission line begins to form multiple coils or spirals. 
         FIG. 7  is a cross-sectional view illustrating one embodiment of a conduit narrowed as it passes through a tool, such that the conduit forms a substantial bond or contact with a transmission cable. 
         FIG. 8  is a perspective cross-sectional view illustrating one embodiment of a box end and pin end of a drill tool comprising an integrated transmission line. 
         FIG. 9  is a perspective cross-sectional view illustrating one embodiment of a transmission line coupled to a pair of transmission elements for communicating across tool joints. 
     
    
    
     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 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. 
     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. 
       FIG. 10  is a cross section view of a drill rig  102  drilling a borehole  103  into the earth  105  using downhole tools (collectively indicated by numeral  10 ) of the present invention. The collection of downhole tools  10  form at least a portion of a drill string  104 . In operation, a drilling fluid is typically supplied under pressure at the drill rig  102  through the drill string  104 . The drill string  104  is typically rotated by the drill rig  102  to turn a drill bit  108  which is loaded against the earth  105  to form the borehole  103 . The pressurized drilling fluid is circulated through the drill bit  108  to provide a flushing action to carry the drilled earth cuttings to the surface. Rotation of the drill bit may alternately be provided by other downhole tools such as drill motors, or drill turbines (not shown) located adjacent to the drill bit  108 . Other downhole tools include drill pipe  110  and downhole instrumentation such as logging while drilling tools  106 , and sensor packages, (not shown). Other useful downhole tools include stabilizers  112 , hole openers, drill collars, heavyweight drill pipe, sub-assemblies, under-reamers, rotary steerable systems, drilling jars, and drilling shock absorbers which are all well known in the drilling industry. 
     Referring now to  FIG. 1 , a drill tool  10 , such as a section of drill pipe  10 ,  110 , may take on the illustrated shape. Due to the linear nature of downhole drilling, a drill string  104  may comprise multiple tool sections  10  having various functions. In an effort to tap into gas, oil, or other mineral deposits, a drill string may be guided or deviate from a linear path. Thus, in selected directional drilling applications, tools  10  may bend or curve to veer off in a desired direction. Since a drill string may consist of many hundreds of sections of drill pipe and other downhole tools, the cumulative bend or curve in each tool may enable a drill string to drill horizontally in some cases. 
     As was previously mentioned, in order to transmit data up and down the drill string  104 , a transmission line  14  may be integrated into a drill tool  10 . If the transmission line  14  is routed straight along the central bore  15  of the drill tool  10 , the transmission line  14  may separate or detach from the inside surface of the central bore  15  when the drill tool  10  bends or curves. This may be undesirable since the transmission line  14  may obstruct or interfere with fluids, wireline tools, concrete, or other objects or substances traveling through the central bore. In fact, in some cases, when a drill tool  10 , such as a section of drill pipe  10 , bends significantly, the transmission line  14  may actually come into contact with the opposite side  17  of the central bore  15 . Thus, apparatus and methods are needed to route a transmission line  14  through the central bore  15  such that the transmission line  14  stays in relatively constant contact with the inside surface of the central bore  15 . 
     Referring to  FIG. 2 , for example, in selected embodiments, a transmission line  14  in accordance with the present invention may be routed in a non-linear path along the inside surface of the central bore  15 . In selected embodiments, the transmission line  14  may take a substantially spiral path around the inside surface of the central bore  15 . This configuration may provide several advantages. For example, in situations where the drill tool  10  bends or curves, the transmission line  14  may stay in substantially continuous contact with the inside surface  15  of the drill tool  10  since the transmission line  14  may flex or bend with the drill tool  10 . Moreover, the spiral-like shape of the transmission line  14  may provide a bias to urge the transmission line  14  against the inside surface of the central bore  15  as will be described in more detail hereinafter. 
     When in a spiral configuration, the transmission line  14  may have relatively few coils. For example, in selected embodiments, there may be between 3 and 5 coils  26   a–c . Since drill tools  10 , such as sections of drill pipe  10 , may reach lengths of more than 30 feet, each coil  26  may span approximately 6 to 10 feet of the drill tool. Nevertheless, any number of coils  26  may be used as desired. 
     The transmission line  14  is not pre-formed into a spiral or other non-linear shape, but simply takes on a spiral shape because it is elastically forced or compelled to fit within the central bore  15  of the downhole tool  10 . Thus, if the transmission line  14  were removed from the drill tool  10 , the transmission line  14  may substantially revert to the shape it had before insertion into the downhole tool  10 . The transmission  14  remains in the elastic mode and is not yielded. Thus, the transmission line  14  may be constructed of resilient materials capable of taking on a spiral or other non-linear shape. This resiliency assists in keeping the transmission line  14  pressed or biased against the inside surface of the central bore  15 , as it is elastically loaded against the wall. Were the transmission line  14  pre-formed into a spiral, the yielding associated with forming the spiral not only significantly reduces the available loading against the wall, but also may change the electrical characteristics of the transmission line  14  or worse, damage it. 
     Another reason for not pre-forming the transmission line  14  into a spiral or other non-linear shape is that doing so may be difficult. As was previously described, in selected embodiments, the coils  26   a–c  may be spaced every 6 to 10 feet. This relatively “lazy” spacing of the coils  26  may be difficult to pre-form into a transmission line  14 . As stated earlier, by not pre-forming the coils  26 , the transmission line  14  may be urged with greater force against the inside diameter of the central bore  15  since the tendency of the transmission line  14  may be to uncoil itself. 
     As illustrated, the ends of the transmission line  14  may be routed through channels  22 ,  24  formed in the pin end  18  and box end  16  of a drill tool  10 . The channels  22 ,  24  may keep the ends of the transmission line  14  rigidly fixed. This enables the coiled or spiral shape of the transmission line  14  to be maintained since, together with the central bore  15 , the channels  22 ,  24  hold the transmission line  14  in its spiral or non-linear shape. 
     Referring to  FIG. 3 , in selected embodiments, a substantially linear transmission line  14  may be initially inserted through a first channel  22  in the box end  16  of the drill tool  10 , through the central bore  15 , and through a second channel  24  in the pin end  18 . The transmission line  14  may be sized such that it extends from the channel  24  a specified length  28 . This additional length  28  may disappear when coils  26  are introduced into the transmission line  14 . 
     Referring to  FIG. 4 , for example, the surplus length  28  of the transmission line may be urged into the central bore  15  of the downhole tool  10 . When this occurs, the transmission line  14  may begin to buckle and a gap  30   a , or separation  30   a , may open up between the transmission line  14  and the inside surface of the central bore  15 . Optionally, a torque  34  or rotation  34  may also be applied to the transmission line  14  to help it form a spiral within the central bore  15 . 
     Referring to  FIG. 5 , as the transmission line  14  is further urged into the central bore  15 , the transmission line  14  may contact the opposite side  35  of the central bore  15 . Since the transmission line  14  may resist buckling further, the transmission line  14  may begin to form a spiral or other non-linear shape within the central bore  15 . 
     Referring to  FIG. 6 , as the transmission line  14  is urged further into the central bore  15 , the transmission line  14  may begin to form several coils  26   a ,  26   b  within the central bore  15 . As was previously discussed, any desired number of coils  26  may be formed in the transmission line  14  according to the length of the transmission line  14  and the length of the drill tool  10 . In certain embodiments, each coil  26  may require approximately 8 inches or so of additional length of transmission line  14 . However, this may vary according to the number of coils  26 , the inside diameter of the central bore  15 , the length of each coil  26 , as well as other factors. 
     Referring to  FIG. 7 , a transmission line  14  may comprise various components. For example, in certain embodiments, the transmission line  14  may include an outer protective conduit  38  and an inner transmission cable  40 , such as a coaxial cable  40 . In selected embodiments, a coaxial cable  40  may include a core conductor  44 , a dielectric core  42 , and a shield  45 . In other embodiments, the transmission cable  40  may comprise one or several conductors, such as copper wires, optical fibers, waveguides, or the like. Any media capable of transmitting a desired signal may be used in accordance with the present invention. Likewise, the protective conduit  38  may be any suitable material, such as metal, certain types of plastics, fiber materials, and the like. In selected embodiments, the protective conduit  38  may be constructed of stainless steel. 
     In certain cases, a conduit  38  used to protect or cover a transmission cable  40  may have an inside diameter larger than the outside diameter of the transmission cable  40 . Thus, in certain embodiments, it may be desirable to improve the bond between the conduit  38  and the cable  40 . This may provide several advantages. For example, an improved bond may keep the transmission cable  14  from moving with respect to the conduit, thereby reducing wear or chafing that may occur between the two. An improved bond may also keep unwanted fluids or other substances from being introduced between the conduit  14  and the cable  40 . 
     In selected embodiments, the diameter of the conduit may be reduced to more closely bond with or contact the cable  40 . For example, the conduit  38  may be narrowed by passage through a tool  46 . This narrowing process may actually thicken the walls of the conduit, thereby providing additional stiffness or resiliency to the conduit  38 . This may be desirable because the added stiffness or resiliency may keep the conduit  38  more firmly pressed against the inside surface of the central bore  15 . In selected embodiments, stainless steel may provide a suitable material for the conduit  38  since it is resistant to corrosion and wear, and is also sufficiently resilient. Nevertheless, other materials may also be used and provide similar qualities. 
     Referring to  FIG. 8 , an enlarged cross-sectional view of the box end  16  and pin end  18  of a drill tool  10  in accordance with the present invention is illustrated. In certain embodiments, channels  22 ,  24  may be gun-drilled or otherwise formed in the box end  16  and pin end  18  of a drill tool  10 . The channels  22 ,  24  may serve to fix the ends of the transmission line  14  and provide a path to connect the transmission line  14  to transmission elements  52   a ,  52   b  mounted in the box end  16  and pin end  18  of the drill tool  10 . Channels  22 ,  24  may be provided in the box end  16  and pin end  18  because thicker walls are present in this area of the drill tool  10 . 
     As was mentioned, the channels  22 ,  24  may provide a convenient location to fix the ends of the transmission line  14 . For example, in selected embodiments, the conduit  38  may be flared (not shown) to keep the transmission line  14  fixed with respect to the channels  22 ,  24 . In other embodiments, keys, wedges, or other components (not shown) may be inserted in the channel  22 ,  24  between the transmission line  14  and the channel  22 ,  24  to keep the transmission line  14  from moving with respect to the channel  22 ,  24 . In reality, any other suitable method of fixing the transmission line  14  with respect to the channels  22 ,  24  may be used and is within the scope of the present invention. 
     As illustrated, transmission elements  52   a ,  52   b  may be installed in the box end  16  and pin end  18  of the drill tool  10 , respectively. Recesses may be milled or otherwise formed in the box and pin end  16 ,  18  to accommodate the transmission elements  52   a ,  52   b . In certain embodiments, the transmission elements  52   a ,  52   b  may be installed in the secondary shoulders  54   a ,  54   b , rather than the primary shoulders  56   a ,  56   b , since the secondary shoulders  54   a ,  54   b  may be more protected from external elements and may also be less subject to stress incident on the primary shoulders  56   a ,  56   b.    
     Referring to  FIG. 9 , the transmission elements  52   a ,  52   b  located in the box end  16  and pin end  18  may communicate with transmission elements  52   c ,  52   c  located in other connected downhole tools. The transmission elements  52   a ,  52   b  may be characterized by an annular shape mountable in recesses formed in the annular ends of a drill tool  10 . The annular shape may provide consistent connectivity between downhole tools  10  since these downhole tools  10  may rotate with respect to one another as they are threaded together. In selected embodiments, the transmission elements  52  may include an outer housing  58  and an inner conductor  60  within the housing  58  and insulated therefrom. 
     In selected embodiments, the transmission elements  52  may communicate by direct electrical contact with one another. A conductor  60  of one transmission element  52  may contact a corresponding conductor  60  located in a corresponding transmission element  52 . In other embodiments, the transmission elements  52  may communicate inductively. That is, the transmission elements  52  may convert electrical signals transmitted along the transmission line  14  to magnetic fields for transmission from one transmission element  52   a  to another  52   c . This may be advantageous in cases where direct electrical contacts are unreliable. 
     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.