Patent Publication Number: US-8118093-B2

Title: Threaded retention device for downhole transmission lines

Description:
BACKGROUND 
     1. Field of the Invention 
     This invention relates to downhole drilling, and more particularly to apparatus and methods for retaining and tensioning transmission lines in downhole tools. 
     2. Description of the Related Art 
     For half a century, the oil and gas industry has sought to develop downhole telemetry systems that enable high-definition formation evaluation and borehole navigation while drilling in real time. The ability to transmit large amounts of sub-surface data to the surface has the potential to significantly decrease drilling costs by enabling operators to more accurately direct the drill string to hydrocarbon deposits. Such information may also improve safety and reduce the environmental impacts of drilling. This technology may also be desirable to take advantage of numerous advances in the design of tools and techniques for oil and gas exploration, and may be used to provide real-time access to data such as temperature, pressure, inclination, salinity, and the like, while drilling. 
     In order to transmit data at high speeds along a drill string, various approaches have been attempted or suggested. One approach that is currently being implemented and achieving commercial success is to incorporate data transmission lines, or wires, into drill string components. These data transmission lines bi-directionally transmit data along the drill string. In certain cases, drill string components may be modified to include high-speed, high-strength data cable running through their central bores. In certain cases, this approach may require placing repeaters or amplifiers at selected intervals along the drill string to amplify or boost the signal as it travels along the transmission lines. 
     In order to implement a “wired” drill string, apparatus and methods are needed to route transmission lines or wires, such as coaxial cable, along or through the central bore of drill string components. Ideally, such apparatus and methods would be able to retain the transmission lines under tension. This will minimize movement of the transmission line within the central bore and minimize interference with tools or debris moving therethrough. Further needed are apparatus and methods to seal and isolate the transmission lines from drilling fluids passing through the central bore of the drill string. Yet further needed are apparatus and methods to quickly install the transmission lines in downhole tools, while minimizing the need for expensive equipment or highly trained personnel. 
     SUMMARY 
     The present invention provides apparatus and methods for retaining and tensioning transmission lines routed through or along downhole tools. The features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by practice of the invention as set forth hereinafter. 
     In a first aspect of the invention, an apparatus for retaining and tensioning an end of a transmission line includes a nut element having internal threads configured to engage an externally threaded transmission line, such as an externally threaded coaxial cable, thereby retaining an end of the transmission line. The internal threads may form a passageway extending from a first end of the nut element to a second end of the nut element. This passageway may allow a transmission line to pass through the nut element. A socket may be incorporated into one end of the nut element to enable a tool to apply torque thereto. 
     In certain aspects, an outer surface of the nut element is substantially cylindrical, allowing the nut element to slide within a cylindrical borehole formed in the downhole tool. Similarly, an outer surface of the externally threaded transmission line may also be substantially cylindrical. In selected embodiments, the outer diameter of the nut element is larger than the outer diameter of the externally threaded transmission line. This will allow the nut element to abut against a counterbore feature in the downhole tool, thereby retaining and maintaining tension in the transmission line. 
     In selected aspects, an elastomeric seal member may be inserted into the passageway of the nut element. This may seal the joint between the externally threaded transmission line and the nut element and also create a seal between the outside diameter of the transmission line and the inside diameter of the tubing. In some aspects of the invention, the transmission line is sheathed or housed within tubing providing “armor” for the transmission line. A screw piece may be provided to thread into the internal threads and compress the elastomeric seal member, thereby providing a high pressure and high temperature air- and/or water-tight seal. In selected embodiments, a socket is incorporated into the screw piece to enable a tool to apply torque thereto. 
     In another aspect, an apparatus in accordance with the invention may include a downhole tool and a transmission line extending through a central bore of the downhole tool. The transmission line may include external threads on an end thereof. A retention device may be provided to secure the transmission line at or near an end of the downhole tool. This retention device may include a nut element having internal threads configured to engage the external threads of the transmission line and abut against a feature of the downhole tool, thereby retaining the end of the transmission line. The internal threads may form a passageway extending from a first end of the nut element to a second end of the nut element. This passageway will enable a transmission line to pass through the nut element. 
     In yet another aspect, a method for securing a transmission line proximate an end of a downhole tool may include routing a transmission line through a central bore of a downhole tool. The method may further include securing the transmission line at or near an end of the downhole tool. In certain embodiments, securing may include threading an internally threaded nut element over the external threads of the transmission line. The internal threads may form a passageway extending from a first end to a second end of the nut element, thereby allowing a transmission line to pass through the nut element. 
     In selected aspects, the method may further include applying torque to a socket incorporated into one of the first and second ends of the nut element. This allows the nut element to thread onto the external threads of the transmission line, thereby retaining the transmission line and potentially increasing tension in the transmission line. The method may further include inserting an elastomeric seal member into the passageway to seal the joint between the transmission line and the nut element. A screw piece may be screwed into the internal threads of the nut element to compress the elastomeric seal member, thereby enhancing the seal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through use of the accompanying drawings, in which: 
         FIG. 1  is a cutaway cross-sectional perspective view of two “wired” downhole tools; 
         FIG. 2  is a cross-sectional perspective view of one embodiment of a threaded retention device incorporated into the pin end of a downhole tool; 
         FIG. 3  is an exploded cross-sectional perspective view of the threaded retention device of  FIG. 2 ; 
         FIG. 4  is an assembled cross-sectional perspective view of the threaded retention device of  FIG. 2 ; 
         FIG. 5A  is a cross-sectional side view of one embodiment of a nut element in accordance with the invention; 
         FIG. 5B  is an end view of the nut element of  FIG. 5A ; 
         FIG. 6A  is a cross-sectional side view of one embodiment of a screw piece in accordance with the invention; 
         FIG. 6B  is an end view of the screw piece of  FIG. 6A ; 
         FIG. 7A  is a cross-sectional side view of one embodiment of threaded tubing for a transmission line in accordance with the invention; 
         FIG. 7B  is an end view of the threaded tubing of  FIG. 7A ; and 
         FIG. 8  is a flow chart of one embodiment of a method for retaining and/or tensioning a transmission line using threaded retention devices in accordance with the invention. 
     
    
    
     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 be easily made without departing from the essential characteristics of the invention, as described in connection with the Figures. Thus, the following description of the Figures is intended only by way of example, and simply illustrates certain selected embodiments consistent with the invention as claimed herein. 
     Referring to  FIG. 1 , one example of a pair of “wired” downhole tools  100   a ,  100   b , configured to transmit data signals along a drill string, is illustrated. In this example, the pin end  102  of a first downhole tool  100   a  (e.g., a first section of drill pipe  100   a ) is configured to thread into the box end  104  of a second downhole tool  100   b  (e.g., a second section of drill pipe  100   b ). A transmission line  106   a ,  106   b  may be incorporated into the first and second downhole tools  100   a ,  100   b  to transmit data signals therealong. In certain embodiments, the transmission lines  106   a ,  106   b  may be incorporated into the walls  108   a ,  108   b  of the downhole tools  100   a ,  100   b  at or near the pin end  102  and box end  104 , since the wall thickness in these areas may be greater. However, the transmission lines  106   a ,  106   b  may be routed into the central bore  110  of the downhole tools  100   a ,  100   b  where the wall thickness is lesser. 
     To transmit data across the tool joint, transmission elements  110   a ,  110   b  may be incorporated into the pin end  102  and box end  104  respectively. For example, where the drill pipe is “double shouldered” drill pipe, as illustrated, a pair of transmission elements may be incorporated into recesses in the secondary shoulders  112   a ,  112   b  of the pin end  102  and box end  104  (as opposed to the primary shoulders  114   a ,  114   b ). These transmission elements  110   a ,  110   b  may communicate using any known method. For example, the transmission elements  111   a ,  110   b  may use direct electrical contacts or inductive coupling to transmit data signals across the tool joint. Additional details regarding the drill pipe that may be used to implement aspects of the invention may be found in U.S. Pat. Nos. 6,670,880, 7,139,218 and 6,717,501, all incorporated herein by reference in their entirety and assigned to the present assignee. 
     Although the downhole tools  100   a ,  100   b  illustrated in  FIG. 1  are sections of drill pipe, the downhole tools  100   a ,  100   b  may include any number of downhole tools, including but not limited to heavyweight drill pipe, drill collar, crossovers, mud motors, directional drilling equipment, stabilizers, hole openers, sub-assemblies, under-reamers, drilling jars, drilling shock absorbers, and other specialized devices, which are all well known in the drilling industry. 
     Referring to  FIG. 2 , as previously mentioned, one potential problem with routing transmission lines  106  through downhole tools  100  is that the transmission lines  106  may interfere with tools, fluids, or debris moving through the central bore  110 . These tools, fluids, or debris may sever or damage the transmission lines  106 , thereby terminating or interrupting the flow of data along the drill string. Thus, apparatus and methods are needed to route transmission lines  106  through downhole tools  100  in a safe and reliable manner. Ideally, such apparatus and methods would be able to maintain tension in the transmission lines  106  to minimize movement within the central bore  110  and minimize interference with tools or other debris moving therethrough. Ideally, such apparatus and methods would enable quick and inexpensive installation of downhole transmission lines  106  in downhole tools  100  without the need for expensive equipment or highly trained personnel. 
       FIG. 2  shows one embodiment of a retention device  200  in accordance with the invention. In this embodiment, the retention device  200  is incorporated into the pin end  102  of a downhole tool  100 , although an equivalent device may also be incorporated into the box end  104  of a downhole tool  100 . The retention device  200  is able to maintain tension in a transmission line  106 , in this example a transmission line  106 , in order to minimize movement within the central bore  110  and minimize interference with tools and/or debris traveling through the central bore  110 . The retention device  200  also enables a transmission line  106  to be quickly and easily installed in a downhole tool  100  without the need for expensive tools or equipment. 
       FIG. 3  is an exploded cross-sectional perspective view of one embodiment of a threaded retention device  200  in accordance with the invention. As shown, in selected embodiments, the retention device  200  may include a nut element  300 , a seal member  304 , and a screw piece  306 . The nut element  300  may include internal threads along an inside diameter thereof to engage externally threaded tubing  302 . In some aspects, the tubing  302  may be configured to provide ‘armor’ for the transmission line  106 . Similarly, the screw piece  306  may include external threads along an outside diameter thereof, allowing it to be threaded into the inside diameter of the nut element  300 . Both the nut element  300  and the screw piece  306  may include a socket, such as a hex socket, incorporated into an end thereof to allow a tool, such as a hex key, to apply torque to the nut element  300  and the screw piece  306  respectively. 
     Each of the nut element  300 , seal member  304 , screw piece  306 , and tubing  302  may include a passageway to allow a transmission line  106  (not shown) to pass therethrough. The transmission line  106  may include coaxial cable, electrical wires, optical fibers, or other conductors or cables capable of transmitting power and/or a signal. Similarly, the tubing  302 , nut element  300 , and screw piece  306  may be fabricated from materials such as steel (e.g., stainless steel), aluminum, titanium, or other suitable materials. 
     Referring to  FIG. 4 , to retain the end of the threaded tubing  302 , the seal member  304  may be inserted into the inside diameter of the tubing  302  and the nut element  300  may be threaded onto the tubing  302 . In selected embodiments, the nut element  300 , seal member  304 , and screw piece  306  may be pre-assembled as a single unit that may be threaded onto the end of the tubing  302 . In certain aspects, the seal member  304  may be fabricated from an elastomer (e.g., Viton or other fluoropolymer elastomer) or other suitable material, and be substantially cylindrical in shape. The outside diameter of the seal member  304  may include a first portion that roughly conforms to the inside diameter of the tubing  302  and a second portion that roughly conforms to the inside diameter of the nut element  300 . This will prevent water or other fluids from passing through the threaded connection. The inside diameter of the seal member  304  may be selected to create a seal with the cable or conductor passing therethrough. This will create a seal between the inside diameter of the tubing  302  and the outside diameter of the cable or conductor. 
     The screw piece  306  may be used to compress the seal member  304  and thereby improve the seal it makes with surrounding elements. That is, as the screw piece  306  is threaded into the nut element  300  towards the seal member  304 , the outside diameter of the seal member  304  will expand to create a more robust seal with the inside diameter of the tubing  302  and the inside diameter of the nut element  300 . The seal member  304  may also compress around the transmission line  106  that passes therethrough. 
     In certain embodiments, the outside diameter of the tubing  302  may be designed to fit snugly within the inside diameter of a hole  400  (e.g., a gun-drilled hole  400 ) of the downhole tool  100 . Similarly, the outside diameter of the nut element  300  may be designed to fit snugly within the inside diameter of an enlarged hole  402  (i.e., a gun-drilled counterbore  402 ) of the downhole tool  100 . The nut element  300  may abut against an edge  404  of the counterbore  402 , thereby enabling the nut element  300  to retain and maintain tension in the transmission line  106 . 
       FIG. 5A  is a cross-sectional side view of one embodiment of a nut element  300  in accordance with the invention. As shown, in certain embodiments, the nut element  300  may be an elongate structure with a substantially cylindrical outside diameter and a threaded inside diameter. The threaded inside diameter is designed to engage the externally threaded transmission line  106  and the threaded screw piece  306 . In selected embodiments, a fine thread series (e.g., UNRF) or extra fine thread series (e.g., UNREF) may be used to provide greater thread contact area. The fine thread series are able to withstand higher tensile loads and are suitable in applications where the wall thickness  502  is limited. A socket  500 , such as a hex socket  500 , may be incorporated into one end of the nut element  300  to allow a tool to apply torque thereto.  FIG. 5B  shows an end view of the nut element  300  of  FIG. 5A . 
       FIG. 6A  is a cross-sectional side view of one embodiment of a screw piece  306  in accordance with the invention. As shown, in certain embodiments, the screw piece  306  may be “headless,” thereby allowing it to be threaded into the nut element  300  a desired distance. The screw piece  306  may be tightened, as needed, to provide a variable amount of compression on the seal member  304 . A face  600  may have sufficient surface area so that it can compress the seal member  304  while avoiding significant extrusion through the inside diameter  602 . Like the nut element  300 , a socket  604 , such as a hex socket  604 , may be incorporated into one end of the screw piece  306 .  FIG. 6B  is an end view of the screw piece of  FIG. 6A . 
       FIG. 7A  is a cross-sectional side view of one embodiment of threaded tubing  302  for a transmission line  106  in accordance with the invention. The tubing  302  may be made of stainless steel or other suitable materials. Depending on the wall thickness, the tubing  302  may require a fine thread series or extra fine thread series. The inside diameter of the tubing  302  may be designed to allow a transmission line to pass therethrough.  FIG. 7B  is an end view of the threaded tubing  302  of  FIG. 7A . 
       FIG. 8  shows one embodiment of a method  800  for installing a transmission line  106  in a downhole tool  100 . In selected embodiments, such a method  800  may include initially inserting  802  a transmission line  106  into a downhole tool  100 . This may include routing the transmission line  106  through the gun-drilled hole of a first end of the downhole tool  100 , through the internal bore  110 , and through the gun-drilled hole of a second end of the downhole tool  100 . Other aspects of the invention may be implemented with the transmission line  106  disposed on the downhole tool  108  using harnesses, combined internal/external line routing, and other suitable means (not shown). The method  800  may then include threading  804  a first retention device  200  onto a first end of the transmission line  106  using an Allen wrench or other suitable tool. In certain cases, the retention device  200  may come pre-assembled with the seal member  304  and screw piece  306  installed. Because the transmission line  106  is not under tension at this point, applying the first retention device  200  to the transmission line  106  may be a relatively simple procedure. 
     Once the first retention device  200  is threaded onto the first end of the transmission line  106 , the transmission line  106  may be placed  806  under tension (e.g., 200 to 1200 lbs. of tension) with a tensioning tool. This may allow a second retention device  200  to be threaded  806  onto the second end of the transmission line  106 . This may be accomplished by inserting the second retention device  200  into the gun-drilled hole and threading  808  it onto the end of the transmission line  106  using an Allen wrench or other tool. The tensioning tool may then release the transmission line  106 . At this point, the retention devices  200  will retain the ends of the transmission line  106  and maintain tension therein. If desired, a locking thread compound may be applied to the threads of the retention devices  200  before they are threaded onto the transmission line  106 , thereby preventing them from loosening. At this point, the screw pieces  306  may be tightened  810  to compress the seal members  304 , thereby sealing the joints between the transmission line  106  and the nut elements  300 . 
     The present invention may be embodied in other specific forms without departing from the essential characteristics disclosed herein. The described aspects are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.