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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 of the Invention 
     In the downhole drilling industry, MWD and LWD tools are used to take measurements and gather information with respect to downhole geological formations, status of downhole tools, conditions located downhole, and the like. 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 accurately tap into oil, gas, or other mineral bearing reservoirs. Data may be gathered at various points along the drill string. For example, sensors, tools, and the like, may be located at or near the bottom hole assembly and on intermediate tools located at desired points along the drill string. 
     Nevertheless, data gathering and analysis do not represent the entire 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 or 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 drill pipe. Due to the inherent nature of drilling, most downhole tools have a similar cylindrical shape defining a central bore. The wall thickness surrounding the central bore is typically designed in accordance with weight, strength, and other constraints imposed by the downhole environment. In some cases, milling or forming a channel in the wall of a downhole tool to accommodate a transmission line may critically weaken the wall. Thus, in certain embodiments, the only practical route for a transmission line is through the central bore of the downhole tool. 
     At or near the box end and pin end of the downhole tool, a transmission line may be routed from the central bore through the tool wall. This may be done for several reasons. First, the box end and pin end are typically constructed with thicker walls to provide additional strength at the tool joints. This added thickness is many times sufficient to accommodate a channel without critically weakening the wall. Second, transmission elements are typically installed in the box end and pin end to transmit information across the tool joints. These transmission elements are typically embedded within recesses formed in the box end and pin end. Thus, channels are needed in the box end and pin end to provide a path for the transmission line between the transmission elements and the central bore of the downhole tool. 
     Thus, what are needed are apparatus and methods for installing channels in the box end and pin end of downhole tools to provide routes for transmission lines traveling between transmission elements and the central bore. 
     What are further needed are improved apparatus and methods for providing a smooth path for a transmission line routed through a downhole tool to prevent kinking or other damage. 
     What are further needed are improved apparatus and methods for effectively drilling or otherwise forming channels in the box end and pin end of a downhole tool. 
     Finally, what are needed are apparatus and methods to minimize the expense and labor required to install these channels in the box end and pin end 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 installing paths or channels in the box end and pin end of a downhole tool to provide a route for a transmission line traveling between transmission elements and the central bore. It is a further object to provide improved apparatus and methods for smoothing the path or route of a transmission line to prevent kinking or other damage to a transmission line routed through a downhole tool. It is yet a further object to provide improved apparatus and methods for effectively drilling or forming channels in the box end and pin end of a downhole tool. Finally, it is a further object to minimize the expense and labor required to form these channels in the box end and pin end of a downhole tool. 
     Consistent with the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a method for routing a transmission line through a tool joint having a primary and secondary shoulder, a central bore, and a longitudinal axis, is disclosed in one embodiment of the invention as including drilling a straight channel, at a positive, nominal angle with respect to the longitudinal axis, through the tool joint from the secondary shoulder to a point proximate the inside wall of the central bore. The method further includes milling back, from within the central bore, a second channel to merge with the straight channel, thereby forming a continuous channel from the secondary shoulder to the central bore. 
     In selected embodiments, drilling includes gun-drilling the straight channel. In other embodiments, the method includes tilting the tool joint before drilling to produce the positive, nominal angle. In selected embodiments, tilting includes adjusting the tilt before drilling to provide a desired positive, nominal angle. In selected embodiments, the positive, nominal angle is less than or equal to 15 degrees. 
     In certain embodiments, the straight channel does not break into the central bore. In other embodiments, the straight channel breaks into the central bore at a non-perpendicular angle. In such embodiments, a backing member may be inserted into the central bore to facilitate drilling into the central bore at the non-perpendicular angle. In other embodiments, milling back includes milling the second channel with a milling tool inserted into the central bore. This milling process may be used to open the straight channel to the central bore. 
     In another aspect of the invention, an apparatus in accordance with the invention includes a tool joint of a downhole tool, wherein the tool joint includes a primary and secondary shoulder, a central bore, and a longitudinal axis. The apparatus further includes a gun-drilled channel formed in the tool joint from the secondary shoulder to a point proximate the central bore, and an open channel milled from the central bore to the gun-drilled channel, such that the gun-drilled channel and the open channel merge to form a continuous channel. 
     In selected embodiments, the gun-drilled channel is drilled at a positive, nominal angle with respect to the longitudinal axis. In some cases, this positive, nominal angle is less than or equal to 15 degrees. In selected embodiments, the gun-drilled channel does not break into the central bore. In other embodiments, the gun-drilled channel breaks into the central bore at a non-perpendicular angle. In yet other embodiments, the gun-drilled channel breaks into the central bore substantially perpendicularly. In some cases, the open channel is milled with a milling tool inserted into the central bore. 
     In another aspect of the invention, a method for routing a transmission line through a tool joint of a downhole tool, wherein the tool joint includes primary and secondary shoulders, a tool wall, a central bore, and a longitudinal axis, includes increasing the inside diameter of a portion of the central bore to provide a first portion having a standard diameter, and a second portion having an enlarged diameter. The method further includes drilling a channel through the tool wall from the secondary shoulder to an exit point within the second portion. 
     In selected embodiments, drilling includes gun-drilling that may or may not break into the central bore. In other embodiments, drilling includes milling back from the central bore to the gun-drilled channel. In certain cases, this milling process opens up the channel to the central bore. In selected embodiments, the channel breaks into the central bore at a non-perpendicular angle. In such cases, a backing member may be inserted into the central bore to facilitate drilling into the central bore at a non-perpendicular angle. In other embodiments, the channel breaks into the central bore at a substantially perpendicular angle. 
     In another aspect of the invention, a method for routing a transmission line through a downhole tool having primary and secondary shoulders, a central bore, and a longitudinal axis, includes drilling a straight channel through the downhole tool from the secondary shoulder to a point proximate the inside wall of the central bore. The method further includes milling back, from within the central bore, a second channel effective to merge with the straight channel, to form a continuous channel from the secondary shoulder to the central bore. 
     In yet another aspect of the invention, a method for routing a transmission line through a tool joint having primary and secondary shoulders, a central bore, and a longitudinal axis, includes drilling a straight channel, at a positive, nominal angle with respect to the longitudinal axis, through the tool joint from the secondary shoulder to the central bore. 
    
    
     
       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 a drill rig in accordance with the invention. 
         FIG. 2  is a cross-sectional view illustrating one embodiment of a transmission line integrated into a downhole tool, such as a section of drill pipe. 
         FIG. 3  is a cross-sectional view illustrating one embodiment of a transmission line integrated into a heavyweight downhole tool, such as a section of heavyweight drill pipe. 
         FIGS. 4A and 4B  are two cross-sectional views illustrating the box end and pin end of a section of drill pipe, wherein part of the central bore is enlarged to provide a shorter path for a transmission line through the tool joint. 
         FIGS. 5A and 5B  are two cross-sectional views of the box end and pin end of a section of drill pipe, wherein channels are only partially drilled through the tool wall. 
         FIGS. 6A and 6B  are two cross-sectional views of the box end and pin end illustrated in  FIGS. 5A and 5B , wherein part of the central bore is enlarged to expose the channels to the central bore. 
         FIGS. 7A and 7B  are two cross-sectional views of the box end and pin end of a section of drill pipe, wherein channels exit perpendicularly into the central bore. 
         FIGS. 8A and 8B  are two cross-sectional views of the box end and pin end of a section of heavyweight drill pipe, wherein channels are drilled into the tool joints and are exposed to the central bore by milling channels into the tool wall from within the central bore. 
         FIGS. 9A and 9B  are two cross-sectional views of the box end and pin end of a section of heavyweight drill pipe, wherein channels are drilled into the tool joints at a positive, nominal angle with respect to the longitudinal axis of the tool joint, and are exposed to the central bore by milling channels into the tool wall from within the central bore. 
         FIG. 10  is a cross-sectional view illustrating one embodiment of a tool used for milling channels into the inside wall of the central bore. 
         FIG. 11  is a cross-sectional view illustrating one embodiment of an apparatus and method for drilling channels into the downhole tool, wherein the channels are drilled at a positive, nominal angle with respect to the longitudinal axis of the downhole tool. 
     
    
    
     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. 
     Referring to  FIG. 1 , a cross-sectional view of a drill rig  10  is illustrated drilling a borehole  14  into the earth  16  using downhole tools (collectively indicated by numeral  12 ). The collection of downhole tools  12  form at least a portion of a drill string  18 . In operation, a drilling fluid is typically supplied under pressure at the drill rig  10  through the drill string  18 . The drill string  18  is typically rotated by the drill rig  10  to turn a drill bit  12   e  which is loaded against the earth  16  to form the borehole  14 . 
     Pressurized drilling fluid is circulated through the drill bit  12   e  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  12   e.  Other downhole tools include drill pipe  12   a  and downhole instrumentation such as logging while drilling tools  12   c,  and sensor packages (not shown). Other useful downhole tools include stabilizers  12   d,  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 to  FIG. 2 , a downhole tool  12   a  may include a box end  24  and a pin end  26 . A pin end  26  may thread into a box end  24 , thereby enabling the connection of multiple tools  12  together to form a drill string  18 . Due to the inherent nature of drilling, most downhole tools  12   a  have a similar cylindrical shape and a central bore  28 . The central bore  28  is used to transport drilling fluids, wireline tools, cement, and the like through the drill string  18 . 
     The wall thickness  36  surrounding the central bore  28  is typically designed in accordance with weight, strength, and other constraints, needed to withstand substantial torque placed on the tool  12   a,  pressure within the central bore  28 , flex in the tool  12   a,  and the like. Because of the immense forces placed on the tool  12   a,  milling or forming a channel in the wall  36  of the downhole tool  12   a  to accommodate a transmission line  30  may excessively weaken the wall. Thus, in most cases, the only practical route for a transmission line  30  is through the central bore  28  of the downhole tool  12   a.    
     Nevertheless, routing the transmission line  30  through the central bore  28  may expose the transmission line  30  to drilling fluids, cements, wireline tools, or other substances or objects passing through the central bore  28 . This can damage the transmission line  30  or create interference between the transmission line  30  and objects or substances passing through the central bore  28 . Thus, in selected embodiments, a transmission line  30  is preferably maintained as close to the wall  36  of the central bore  28  as possible to minimize interference. In selected embodiments, the transmission line  30  is protected by a conduit  30  or other protective covering  30  to protect the internal transmission medium (e.g. wire, fiber, etc.). 
     As illustrated, at or near the box end  24  and pin end  26  of the tool  12   a,  the central bore  28  may be narrower and the surrounding tool wall  38  may be thicker. This increases the strength of the downhole tool  12   a  at or near the tool joints, which undergo a great deal of stress during drilling. In addition, the added thickness  38  may enable channels  32 ,  34 , to be milled or formed in the walls  38  to accommodate a transmission line  30  without critically weakening the tool  12   a.  The channels  32 ,  34  may exit the downhole tool  12   a  at or near the ends of the tool  12   a,  where the transmission line  30  may be coupled to transmission elements (not shown) to transmit information across the tool joints. 
     Referring to  FIG. 3 , in contrast to the downhole tool  12   a  illustrated in  FIG. 2 , certain downhole tools  12   c  may be characterized by a tool wall  40  of greater thickness. For example, at or near the bottom hole assembly  12   e,  a drill string  18  may include various heavyweight tools  12   c,  such as heavyweight drill pipe  12   c  or sections of drill collar  12   c.  Such tools  12   c  may have a central bore  28  having a substantially constant inside diameter between the box end  24  and the pin end  26 . Due to the substantially constant diameter of the central bore  28 , a distinct solution is needed to route a transmission line  30  through the downhole tool  12   c.  For example, in selected embodiments, as illustrated, a transmission line  30  may be routed such that it bends or angles away from the longitudinal axis  11  of the tool  12   c  at or near the box and pin ends  24 ,  26 . The transmission line  30  travels through the central bore  28  along the central portion of the tool  28 . At or near the box end  24  and pin end  26 , the transmission line  30  is routed into channels  32 ,  34  to connect to transmission elements (not shown). Because of the unique configuration of the downhole tool  12   c,  novel apparatus and methods are needed to create the channels  32 ,  34  and route the transmission line  30  in a manner that avoids kinking or other damage to the transmission line  30 . 
     Referring to  FIGS. 4A and 4B , in drill tools  12   a  like that described with respect to  FIG. 2 , a transmission line  30  may travel through channels  32 ,  34  formed in the box end  24  and pin end  26  of a downhole tool  12   a.  As illustrated, the box end  24  and pin end  26  may include primary shoulders  20   a,    20   b  and secondary shoulders  22   a,    22   b.  In operation, the primary shoulders  20   a,    20   b  may absorb the majority of the stress imposed on the tool joint. Nevertheless, the secondary shoulders  22   a,    22   b  may also absorb a significant, although lesser, amount of stress. Because of the lower stress, and also because the secondary shoulders  22   a,    22   b  are more internally protected than the primary shoulders  20   a,    20   b,  transmission elements may be located on the secondary shoulders  22   a,    22   b.    
     In selected embodiments, it may be desirable to shorten the channels  32 ,  34  between the transmission elements and the central bore  28  as much as possible to conserve the time and expense of creating the channels  32 ,  34 . For example, in some downhole tools  12   a,  the channels  32 ,  34  may be formed by gun-drilling the box end  24  and pin end  26 . Normally, a box end  24  or pin end  26  is characterized by a restricted bore  50   a,    50   b  having a narrower diameter, and an expanded bore  52   a,    52   b  having a larger diameter. The expanded bore  52   a,    52   b  is typically sized to mate with and roughly equal the diameter of the central bore  28  of the drill tool  12   a.  Between the restricted bore  50  and the expanded bore  52  is typically a transition region  54   a,    54   b  where the restricted bore  50  transitions to the expanded bore  52 . To prevent tools, drilling fluids, or other substances from lodging themselves within the central bore  28 , the transition region  54  is typically configured to provide a smooth or graded transition between the restricted bore  50  and the expanded bore  52 . 
     In selected embodiments, the channels  32 ,  34  may be formed in the box end  24  and pin end  26  through the tool wall surrounding the restricted bore  50   a,    50   b.  When the channels  32 ,  34  reach the transition regions  54   a,    54   b,  the channels break through the tool wall into the expanded bore  52   a,    52   b.  Because the length of the restricted bore  50   a,    50   b  is roughly proportional to the length of the channels  32 ,  34  traveling though the tool wall, the channels  32 ,  34  may be shortened by shortening the restricted bore  50  and lengthening the expanded bore  52 . This provides a desired effect since the process of gun-drilling may be costly and time-consuming. Thus, apparatus and methods are needed to reduce or shorten the channels  32 ,  34 . 
     Referring to  FIGS. 5A and 5B , for example, in selected embodiments, the restricted bore  50  may extend a specified distance through the box end  24  and pin end  26 . The channels  32 ,  34  may be drilled through only a portion of the tool wall, but not actually exit into the central bore  28 . 
     Referring to  FIGS. 6A and 6B , once the channels  32 ,  34  are drilled or formed, portions of the tool wall  60  may be removed by counter-boring the restricted bore  50 , thereby exposing the channels  32 ,  34  to the central bore  28 . Thus, the length of the channels  32 ,  34  and the distance drilled may be reduced. In other embodiments, the restricted bore  50  may be shortened before drilling the channels  32 ,  34 . In yet other embodiments, the box end  24 , the pin end  26 , or both, may be redesigned to have a restricted bore  50  of a reduced length, thereby reducing the distance needed to drill the channels  32 ,  34 . In selected embodiments, a drill bit, such as may be used for gun-drilling, may be damaged if it breaks into the central bore, or if it breaks into the central bore at a non-perpendicular angle. In such cases, a backing plate (not shown) or other material may be inserted into the central bore when drilling the channels  32 ,  34 . This may prevent the drill bit from breaking out of the tool wall into the central bore  28 . 
     Referring to  FIGS. 7A and 7B , in another embodiment, a box end  24  and pin end  26  may be designed such that the channels  32 ,  34  break into the enlarged bore  52  at a right angle. This may be accomplished by making the transition regions  54   a,    54   b  substantially perpendicular to the longitudinal axis  11  of the downhole tool  12 . Thus, in some embodiments, a drill bit, such as a drill bit used for gun-drilling, may break into the enlarged bore at a right angle, thereby preventing damage to the bit. Nevertheless, this configuration may be undesirable in some applications, since the transition regions  54   a,    54   b  may hinder the passage of tools or other substances passing through the central bore  28  of a downhole tool  12 . 
     Referring to  FIGS. 8A and 8B , in applications where the central bore  28  is relatively constant, such as may be found in heavyweight drill pipe or drill collar, channels  32 ,  34  are needed to route a transmission line through such tools. Nevertheless, because of the constant or near constant bore  28  of the tool, other methods are needed to provide a route for a transmission line. For example, in contrast to the drill tool illustrated in  FIGS. 4A and 4B , the drill tool illustrated in  FIGS. 8A and 8B  lacks a transition region  54   a,    54   b  where the channels  32 ,  34  can exit into the central bore  28 . 
     In selected embodiments, channels  32 ,  34  may be initially drilled in the tool wall of the box end  24  and pin end  26 . The channels  32 ,  34  may be drilled such that they do not exit or break into the central bore  28 , thereby preventing damage to the drill bit. In selected embodiments, the channels  32 ,  34  may be drilled substantially parallel to the longitudinal axis  11  of the downhole tool  12 . Once the channels  32 ,  34  are drilled, open channels  66  may be milled into the inside wall of the central bore  28  to open up the channels  32 ,  34  to the central bore  28 . 
     In selected embodiments, the open channels  66  may be shaped to provide a smooth transition for a transmission line routed between the channels  32 ,  34  and the central bore  28 . For example, the open channels  66  may include a first surface  68  substantially parallel to the channels  32 ,  34 , and a curve  74  or bend  74  to guide the transmission line towards the central bore  28 . Likewise, a second bend  74  or curve  74  may enable a transmission line to gently bend from the open channel  66  to a position along the inside wall of the central bore  28 . Thus, the open channel  66  may be shaped, as needed, to prevent kinking or other damage to a transmission line. 
     Referring to  FIGS. 9A and 9B , in another embodiment, channels  32 ,  34  may be drilled at a nominal angle  76  with respect to and toward, the longitudinal axis  11  of the downhole tool from the secondary shoulder towards the central bore  28 . The angle  76  is a positive, nominal angle with respect to the longitudinal axis  11 , but is by design greater than a “zero” degree angle, which may be canted slightly due to variations caused by hole tolerances. The angle  76  may be limited by the geometry of the box end  24  and pin end  26  in some cases, but is generally oriented greater than about 0.25 degrees in a positive direction, toward the longitudinal axis  11 . For example, the angle  76  may be limited by the angle of the threaded portion of the box end  24 . In some cases, the angle  76  of the channels  32 ,  34  may form an angle of less than or equal to 15 degrees with respect to the longitudinal axis  11  of the downhole tool. In a preferred embodiment, the positive angle  76  is between about 0.25 degrees and about 15 degrees. 
     In selected embodiments, the channels  32 ,  34  may be drilled such that they do not actually break into the central bore  28  to prevent damage to the drill bit. Once the channels  32 ,  34  are drilled, a milling tool (not shown) may be inserted into the central bore  28  to open up the channels  32 ,  34  to the central bore  28 . For example, open channels  66  may be milled in the wall of the central bore  28  to open up the channels  32 ,  34  and to provide a smooth transition for a transmission line routed from the channels  32 ,  34  to the central bore  28 . 
     Referring to  FIG. 10 , a milling tool  78 , as was previously mentioned with respect to  FIGS. 8A ,  8 B,  9 A, and  9 B, may be inserted into the central bore  28  of a downhole tool  12 . The milling tool  78  may include a milling bit  80  that may be used to mill the open channel  66  into the wall of the central bore  28 . To form the open channel  66 , the milling tool may be moved in various directions  81  as needed, and may or may not be computer controlled to provide accurate movement. 
     Referring to  FIG. 11 , as was previously mentioned with respect to  FIGS. 9A and 9B , the channels  32 ,  34  may be drilled at an angle  86  with respect to the longitudinal axis  11  of the tool  12 . Since drilling machinery  88 , such as machinery  88  used for gun-drilling, may be large and complex, the drill tool  12  may be tilted at a desired angle  84  with respect to the drilling machine  88 . In selected embodiments, an adjustable arm  86  may be used to support one end of the drill tool  12 . The height of the adjustable arm  86  may be adjusted as needed to adjust the angle  84  of the drill tool with respect to the drill bit  82 . 
     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.

Summary:
A method for routing a transmission line through a tool joint having a primary and secondary shoulder, a central bore, and a longitudinal axis, includes drilling a straight channel, at a positive, nominal angle with respect to the longitudinal axis, through the tool joint from the secondary shoulder to a point proximate the inside wall of the centtral bore. The method further includes milling back, from within the central bore, a second channel to merge with the straight channel, thereby forming a continuous channel from the secondary shoulder to the central bore. In selected embodiments, drilling is accomplished by gun-drilling the straight channel. In other embodiments, the method includes tilting the tool joint before drilling to produce the positive, nominal angle. In selected embodiments, the positive, nominal angle is less than or equal to 15 degrees.