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FEDERAL RESEARCH STATEMENT  
       [0001]     This invention was made with government support under Contract No. DE-FC26-97FT343656 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 along downhole drilling strings.  
         [0004]     2. Background of the Invention  
         [0005]     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 an 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.  
         [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 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.  
         [0008]     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 the downhole tool to accommodate the transmission line may excessively weaken the wall. Thus, in certain embodiments, the only practical route for the transmission line is through the central bore of a downhole tool.  
         [0009]     Nevertheless, routing the transmission line through the central bore may expose the transmission line to drilling fluids, cements, wireline tools, or other substances or objects passing through the central bore. This can damage the transmission line or cause the transmission line to interfere with objects or substances passing through the central bore. Moreover, in directional drilling applications, downhole tools may bend slightly as a drill string deviates from a straight path. This may cause the transmission line to deviate away from the inside surface of the central bore, thereby worsening the obstruction within the central bore.  
         [0010]     Thus, what are needed are apparatus and methods to protect a transmission line, routed through the central bore of a downhole tool, from drilling fluids, cement, wireline tools, or other components traveling through the central bore.  
         [0011]     What are further needed are apparatus and methods to maintain a transmission line against the inside surface of the central bore even when the downhole tool bends or deviates from a linear path.  
         [0012]     What are further needed are apparatus and methods for lining the inside surface of the central bore to isolate a transmission line from objects or substances traveling through the central bore.  
       SUMMARY OF INVENTION  
       [0013]     In view of the foregoing, it is a primary object of the present invention to provide apparatus and methods for protecting a transmission line, routed through the central bore of a downhole tool, from drilling fluids, cement, wireline tools, or other components traveling through the central bore. If is a further object to maintain a transmission line against the inside surface of the central bore even when the downhole tool bends or deviates from a straight path. It is yet a further object to provide apparatus and methods for lining the inside surface of the central bore to isolate a transmission line from objects or substances traveling through the central bore.  
         [0014]     Consistent with the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a liner insertable into the central bore of a downhole tool, wherein the central bore has a standard diameter along a central portion of the tool, and a narrower diameter near the ends of the downhole tool, is disclosed in one embodiment of the invention as including a resilient material rolled into a substantially cylindrical shape. The outside diameter of the resilient material is variable to allow the resilient material to move through the narrower diameter of the central bore. Once past the narrower diameter of the central bore, the outside diameter of the resilient material self-expands within the standard diameter of the downhole tool.  
         [0015]     In selected embodiments, the outside diameter of the resilient material expands to contact the inside surface of the central bore. In other embodiments, a transmission line is routed between the central bore and the outside diameter of the resilient material. The resilient material may keep the transmission line in contact with the inside surface of the central bore. The resilient material may also be effective to protect the transmission line from materials traveling through the central bore.  
         [0016]     In certain embodiments, a channel is formed in the resilient material to accommodate the transmission line. In other embodiments, the resilient material includes two mating surfaces that come together to form the cylindrical shape. Movement between these mating surfaces is effective to cause a change in diameter of the resilient material. In selected embodiments, the mating surfaces are sealed together to prevent substances from leaking into or out of the liner. In certain embodiments, once the resilient material has expanded within the central portion of the downhole tool, the resilient material is maintained in place by shoulders in the central bore.  
         [0017]     In another aspect of the invention, a method for lining the central bore of a downhole tool, wherein the central bore has a central portion of a standard diameter, and tool ends of a narrower diameter, includes rolling a resilient material into a substantially cylindrical shape. The resilient material is then inserted into the central bore through the one of the tool ends into the central portion of the central bore. Once in place, the diameter of the resilient material self-expands within the central portion of the central bore.  
         [0018]     In selected embodiments, the method includes expanding, by the resilient material, the outside diameter of the resilient material to contact the inside surface of the central bore. In other embodiments, the method includes routing a transmission line between the central bore and the outside diameter of the resilient material. The resilient material may maintain contact between the transmission line and the inside surface of the central bore. The resilient material may also protect the transmission line from materials traveling through the central bore.  
         [0019]     In selected embodiments, the method may include forming a channel in the resilient material to accommodate the transmission line. In other embodiments, the resilient material includes two mating surfaces that mate together to form the cylindrical shape. The diameter of the resilient material may be varied by moving the mating surfaces with respect to one another. In selected embodiments, the method may further include sealing the mating surfaces to one another to prevent substances from leaking into or out of the liner.  
         [0020]     In another aspect of the invention, a method for lining the central bore of a downhole tool includes providing a resilient liner having a substantially cylindrical shape and an outside diameter sized to fit within the central bore. The method further includes inserting the resilient liner into the central bore and expanding, by the resilient material, the outside diameter of the resilient material within the central bore. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0021]     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.  
         [0022]      FIG. 1  is a cross-sectional view illustrating one embodiment of a drill rig in accordance with the invention.  
         [0023]      FIG. 2  is a cross-sectional view illustrating one embodiment of a transmission line integrated into a downhole tool.  
         [0024]      FIG. 3  is a cross-sectional view illustrating one embodiment of a transmission line routed through the central bore of a downhole tool when the downhole tool is curved or bent as is customary in directional drilling applications.  
         [0025]      FIG. 4  is a perspective view illustrating one embodiment of a downhole tool liner in accordance with the invention.  
         [0026]      FIG. 5  is a perspective view illustrating one embodiment of a downhole tool liner in accordance with the invention as it is initially inserted into the central bore of a downhole tool.  
         [0027]      FIG. 6  is a cross-sectional view illustrating one embodiment of a downhole tool liner as it is initially inserted into the central bore of a downhole tool.  
         [0028]      FIG. 7  is a cross-sectional view illustrating one embodiment of a downhole tool liner after it expands into the larger diameter of the central bore.  
         [0029]      FIG. 8  is a cross-sectional view illustrating one embodiment of a downhole tool liner within the central bore of a downhole tool, wherein the liner is used to isolate a transmission line from objects or substances passing through the central bore.  
         [0030]      FIG. 9  is a cross-sectional view illustrating one embodiment of a downhole tool liner inserted into the central bore of a downhole tool, wherein the liner includes a channel to accommodate a transmission line. 
     
    
     DETAILED DESCRIPTION  
       [0031]     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.  
         [0032]     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.  
         [0033]     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 ) in accordance with the present invention. 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 .  
         [0034]     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, subassemblies, under-reamers, rotary steerable systems, drilling jars, and drilling shock absorbers, which are all well known in the drilling industry.  
         [0035]     Referring to  FIG. 2 , a downhole tool  12  may include a box end  36  and a pin end  36 . A pin end  38  may thread into a box end  36 , thereby connecting multiple tools  12  together to form a drill string  18 . Due to the inherent nature of drilling, most downhole tools  12  are characterized by a similar cylindrical shape defining a central bore  35 . The central bore is used to transport drilling fluids, wireline tools, cement, and the like down the drill string  18 .  
         [0036]     The wall thickness  39  around the central bore  35  is typically designed in accordance with weight, strength, and other constraints, needed to withstand substantial torque placed on the tool  12 , pressure within the central bore  35 , flex in the tool  12 , and the like. Because of immense forces placed on the tool  12 , milling or forming a channel in the wall of the downhole tool  12  to accommodate a transmission line  34  may excessively weaken the wall. Thus, in selected embodiments, the only practical route for a transmission line  34  is through the central bore  35  of the downhole tool  12 .  
         [0037]     Nevertheless, routing the transmission line  34  through the central bore may expose the transmission line  34  to drilling fluids, cements, wireline tools, or other substances or objects passing through the central bore  35 . This can damage the transmission line  34  or cause the transmission line  34  to negatively interfere with objects or substances passing through the central bore  35 . Thus, in selected embodiments, a transmission line  34  is preferably maintained as close to the wall  39  of the central bore  39  as possible to minimize interference. In selected embodiments, the transmission line  34  is protected by a conduit  34  or other protective covering  34  to protect it from damage.  
         [0038]     As illustrated, at or near the box end  36  and pin end  38  of the tool  12 , the central bore  35  may be narrower and the walls  41  may be thicker. This may increase the strength of the downhole tool  12  at or near the tool joints. In addition, this added thickness  41  may enable channels to be milled or formed in the walls  42 ,  44 , to accommodate a transmission line  34  without overly weakening the downhole tool  12 . The channels  42 ,  44  may exit the downhole tool at or near the ends of the downhole tool  12 , where the transmission line  34  may be coupled to transmission elements (not shown) for communicating across tool joints.  
         [0039]     Referring to  FIG. 3 , In an effort to tap into gas, oil, or other mineral deposits, a drill string  18  may be guided or deviate from a linear path. Thus, in selected directional drilling applications, tools  12  may bend to veer off in a desired direction at an angle  32 . Since a drill string  18  may consist of many hundreds of sections of drill pipe  12  and other downhole tools  12 , the cumulative bend or curve in each tool  12  may enable a drill string  18  to drill horizontally in some cases.  
         [0040]     As was previously mentioned, in order to transmit data up and down the drill string  18 , a transmission line  34  may be integrated into a downhole tool  12 . If the transmission line  34  is routed through the central bore  35  of the downhole tool  12 , the transmission line  34  may separate or detach from the inside surface of the central bore  35  when the downhole tool  12  bends. This may create problems since the transmission line  34  may then 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 downhole tool  12 , such as a section of drill pipe  12 , bends significantly, the transmission line  34  may actually come into contact with the opposite side  37  of the central bore  35 . Thus, apparatus and methods are needed to route a transmission line  34  through the central bore  35  such that the transmission line  34  stays in relatively constant contact with the inside surface of the central bore  35  even when the downhole tool  12  bends.  
         [0041]     Referring to  FIG. 4 , in selected embodiments, a liner  46  may be provided to line the inside surface of the central bore  35 . The liner  46  may be used to protect or isolate the transmission line  34  from substances or objects passing through the central bore  35 . As illustrated, a liner  46  may be formed from a rolled material and have a substantially cylindrical shape.  
         [0042]     In selected embodiments, the liner  46  may include mating surfaces  50 ,  52  that contact one another to form the cylinder. The mating surfaces  50 ,  52  may move with respect to one another to roll the liner  46  more tightly to provide a smaller diameter  54 . Thus, the diameter  54  of the liner may be adjusted as needed. This may be helpful to initially insert the liner  46  into the central bore  35  of a downhole tool  12 . The liner may be constructed of any suitable resilient material capable of withstanding the wear of a downhole environment. For example, a liner  46  may be constructed of a material such as metal, plastic, or the like, having sufficient durability and resiliency.  
         [0043]     Referring to  FIG. 5 , a liner  46  like that described in Figure  4  may be inserted into either the box end  36  or pin end  38  of a downhole tool  12 . As illustrated, a pin end  38  may include a primary  60  and secondary shoulder  58 , and a threaded portion  55 , which may contact another downhole tool  12 . The primary shoulder  60  may absorb the majority of the stress at the tool joint. Nevertheless the secondary shoulder  58  may also absorb some of the stress at the tool joint. The two shoulders  58 ,  60  together may create a stronger tool joint than either shoulder by itself.  
         [0044]     As illustrated, a transmission element  56  may be installed into the secondary shoulder  58 . The transmission element  56  may be used to transmit a signal across the tool joint by communicating with a corresponding transmission element  56  located on another downhole tool  12  (not shown). The transmission element  56  may transmit energy in several different ways. For example, in selected embodiments, the transmission element  58  may transmit electrical energy by direct electrical contact another transmission element  58 .  
         [0045]     In other embodiments, the transmission element  58  may communicate inductively. That is, the transmission element  58  may convert an electrical signal to magnetic energy for transmission across the tool joint. The magnetic energy may then be converted back to an electrical signal by another transmission element  58 . To accommodate the transmission element  58 , a recess may be formed in the secondary shoulder  58 . The transmission line  34  may connect to the transmission element  58  through the channel  44  in the pin end  38 .  
         [0046]     As was previously mentioned, the central bore  35  traveling through the pin end  38  may be narrower than the central bore  35  traveling through the central portion of the tool  12 . Thus, in order to insert the liner  46  into the downhole tool  12 , the diameter  54  of the liner  46  may be reduced. This may be accomplished by rolling the liner  46  into a smaller cylinder. The liner  46  may then be inserted in a direction  62  into the downhole tool  12 . In selected embodiments, the liner  46  may be lubricated to facilitate sliding the liner  46  into the tool  12 .  
         [0047]     Referring to  FIG. 6 , a cross-sectional view of a liner  46  is illustrated as it is inserted into a downhole tool  12 . As shown, the liner  46  may be inserted with an initial diameter  54  so it can slide through the narrow bore  64  in either the box end  36  or pin end  38 . The liner  46  may be cut to a specified length  66  to fit within a central portion  66  of the downhole tool  12 .  
         [0048]     Referring to  FIG. 7 , once the liner  46  reaches the central portion  66  of the central bore  35 , the diameter  54  of the liner  46  may increase to contact the inside surface of the central bore  35 . As was previously described, the liner  46  may self-expand within the central bore  35  due to its resiliency. For example, if the liner  46  is a sheet of a resilient material rolled into a cylindrical shape, the diameter  54  of the liner  46  may automatically expand due to its resiliency.  
         [0049]     Once the diameter  54  of the liner  46  has expanded to contact the inside surface of the central bore  35 , the liner  46  may kept in place  12  by shoulders  68   a ,  68   b  near the box and pin ends  36 ,  38 . The shoulders  68   a ,  68   b  may be present where the central bore  15  narrows near the box end  36  and pin end  38 . Likewise, the resiliency of the liner  46  may keep the liner  46  from slipping past the shoulders  68   a ,  68   b . In selected embodiments, the more resilient the material  46 , the better the retention between the shoulders  68   a ,  68   b.    
         [0050]     It is important to securely retain the liner  46  between the shoulders  68   a ,  68   b . For example, if the liner  46  slips past the shoulders  68   a ,  68   b , the liner  46  may create an obstruction within the central bore  15 . This may cause the drill string to malfunction, possibly causing time-consuming and costly delays. In other embodiments, the liner  46  may be welded or otherwise bonded to the inside of the downhole tool  12  to keep it from moving.  
         [0051]     Referring to  FIG. 8 , a cross-sectional view of the central portion  66  of a downhole tool  12  is illustrated. As shown, the transmission line  34  may be sandwiched between the liner  46  and the surface of the central bore  35 . This may protect the transmission line  34  from objects or substances passing through the central bore  35 . In selected embodiments, the mating surfaces  50 ,  52  may be sealed together to prevent fluids or other substances from leaking from the liner  46 . In other embodiments, the mating surfaces  50 ,  52  may be left unsealed.  
         [0052]     Referring to  FIG. 9 , in other embodiments, a channel  70  may be formed in the liner  46  to accommodate the transmission line  34 . The channel  70  may maintain the transmission line  34  in place and provide better contact between the liner  46  and inside surface of the central bore  35 .  
         [0053]     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 liner insertable into the central bore of a downhole tool includes a resilient material rolled into a substantially cylindrical shape. The outside diameter of the liner is variable to allow the liner to be inserted into a narrowed bore of the downhole tool near the box end or pin end. Once past the narrowed bore, the outside diameter of the liner self-expands within the central bore of the downhole tool. The outside diameter of the liner may expand to contact the inside surface of the central bore. In selected embodiments, a transmission line may be routed between the central bore and the outside diameter of the resilient material. The liner may be effective to protect the transmission line from materials traveling through the central bore.