Patent Publication Number: US-6981546-B2

Title: Electrical transmission line diametrical retention mechanism

Description:
FEDERAL SPONSORSHIP 
     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 
     The present invention relates to the field of retention mechanisms of electrical transmission lines, particularly retention mechanisms for coaxial cables. The preferred mechanisms are particularly well suited for use in difficult environments wherein it is desirable to retain a transmission line without the normal means available such as brackets, screws and such. One such application is in data transmission systems for downhole environments, such as along a drill string used in oil and gas exploration or along the casings and other equipment used in oil and gas production. 
     The goal of accessing data from a drill string has been expressed for more than half a century. As exploration and drilling technology has improved, this goal has become more important in the industry for successful oil gas, and geothermal well exploration and production. For example, to take advantage, of the several advances in the design of various tools and techniques for oil and gas exploration, it would be beneficial to have real time data such as temperature, pressure, inclination, salinity, etc. Several attempts have beau made to devise a successful system for accessing such drill string data. One such system is disclosed In co-pending U.S. Application Ser. No. 09/909,469 (also published as PCT Application WO 02/06716), now U.S. Pat. No. 6,717,501. which is assigned to the same assignee as the present invention. The disclosure of this U.S. Application Ser. No. 09/909,469, now U.S. Pat. No. 6,717,501, is incorporated herein by reference, Another such system is disclosed in co-pending U.S. application Ser. No. 10/358,099 the title of which is DATA TRANSMISSION SYSTEM FOR A DOWNHOLE COMPONENT filed on Feb. 3, 2003. The disclosure of this U.S. Application Ser. No. 10/358,099; now U.S. Patent Publication No. US20040149471A1, is herein incorporated by reference. 
     SUMMARY 
     Briefly stated, the invention is a system for retaining an electrical transmission line through a string of downhole components. 
     In accordance with one aspect of the invention, the system includes a plurality of downhole components, such as sections of pipe in a drill string. Each component has a first and second end, with a first communication element located at the first end and a second communication element located at the second end. Each communication element includes a first contact and a second contact. The system also includes a coaxial cable running between the first and second communication elements, the coaxial cable having a conductive tube and a conductive core within it. The system also includes a first and second connector for connecting the first and second communication elements respectively to the coaxial cable. Each connector includes a conductive sleeve, lying concentrically within the conductive tube, which fits around and makes electrical contact with the conductive core. The conductive sleeve is electrically isolated from the conductive tube. The conductive sleeve of the first connector is in electrical contact with the first contact of the first communication element, the conductive sleeve of the second connector is in electrical contact with the first contact of the second communication element, and the conductive tube is in electrical contact with both the second contact of the first communication element and the second contact of the second communication element. 
     In accordance with another aspect of the invention, the drill components are sections of drill pipe, each having a central bore, and the first and second communication elements are located in a first and second recess respectively at each end of the drill pipe. The system further includes a first passage passing between the first recess and the central bore and a second passage passing between the second recess and the central bore. The first and second connectors are located in the first and second passages respectively. Preferably, each section of drill pipe has a portion with an increased wall thickness at both the box end and the pin end with a resultant smaller diameter of the central bore at the box end and pin end, and the first and second passages run through the portions with an increased wall thickness and generally parallel to the longitudinal axis of the drill pipe. The box end and pin end is also sometimes referred to as the box end tool joint and pin end tool joint. 
     In accordance with another aspect of the invention, the components are sections of drill pipe, drill collars, jars, and similar components that would be typically found in a drill string. This invention is particularly useful when such drill components have a substantially uniform internal diameter. A through passage in the increased wall of a pin end and box end tool joint as described above is not always possible with different size pipes and other types of drill components. Another retention mechanism other than that described above must be employed. One such retention mechanism is overlapping slots which are particularly useful to affix the coaxial cable to the inside wall of the pipe. The overlapping slots replace the need for a passageway connecting the first and second recess to the central bore or internal diameter of the drill component. A system of overlapping slots is placed near each box end and pin end tool joint. 
     In accordance with another aspect of the invention, the system includes a first and second expansion plug, each of which includes a central passage and each of which is press-fit within the conductive tube so as to maintain the increased outside diameter of the conductive tube within the larger diameter portions of the first and second passages respectively. The system also preferably includes a first and second retaining plug, each of which includes ridges on its outer surface to retain the expansion plugs in place. 
     The expansion plugs could alternatively be internal diametrical expansion mandrels with a central passage, the expansion mandrel having a front and back end. The back end of the expansion mandrel has an outer diameter that is greater than an outer diameter of the front end of the expansion mandrel. The retention plugs could alternatively be expansion mandrels with the back end having external circumferentially grooved barbs, also known as a barbed expansion mandrel, that dig into the conductive tube internal diameter. These expansion mandrels become electrical transmission line retainers when displaced within an electrical transmission line. The central passage of the expansion mandrels or retainers could also be electrically insulated allowing bare wire to pass through without causing an electrical short. 
     In accordance with another aspect of the invention, the method includes expanding the outside diameter of the conductive tube by inserting an expansion plug or mandrel into each end. The first and second communication elements each include an inductive coil having at least one loop of wire. In each communication element, a first end of the wire is in electrical contact with the conductive tube and a second end of the wire is in electrical contact with the conductive sleeve. The method further includes inserting a water-tight seal between the second end of the wire and the inside of the conductive tube. 
     In accordance with another aspect of the invention, the method includes affixing the conductive tube to the inside diameter of the drill component. After the above mentioned expansion mandrel is inserted into the conductive tube, the conductive tube is then inserted in one end of the overlapping slots in the drill component and stretched far enough to place the other end of the conductive tube in the opposite end of the drill component. 
     The present invention, together with attendant objects and advantages, will be best understood with reference to the detailed description below in connection with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is cross-sectional view of a drill component exhibiting the overlapping slots. 
         FIG. 2  is a cross-sectional view of a drill component showing the electrical transmission line in place. 
         FIG. 3  is an enlarged cross sectional view or the pin end of a drill component as depicted in FIG.  1 . 
         FIG. 4  is an enlarged cross-sectional view showing the pin end of FIG.  1  and the shoulder. 
         FIG. 5  is an enlarged view of the pin end of a drill component as depicted in  FIG. 1  showing more than one slot. 
         FIG. 6  is an enlarged cross-section of a pin end of a drill component further showing the created shoulder and undercut. 
         FIG. 7  is an enlarged cross-section of a pin end of a drill component showing multiple slots. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
     It should be noted that, as used herein, the term “downhole” is intended to have a relatively broad meaning, including such environments as drilling in oil and gas, gas and geothermal exploration, the systems of casings and other equipment used in oil, gas and geothermal production. 
     It should also be noted that the term “transmission” as used in connection with the phrase data transmission or the like, is intended to have a relatively broad meaning, referring to the passage of signals in at least one direction from one point to another. 
     Referring to the drawings,  FIG. 1  is a cross-sectional view of a drill component exhibiting the overlapping slots of the present invention. The most preferred application of the retention mechanism is in the data transmission system in sections of drill pipe, which make up a drill string used in oil and gas or geothermal exploration. 
     The depicted section  20  of  FIG. 1  includes a pin end  21  and a box end  22 . Between the pin end  21  and box end  22  is the body of the section. A typical length of the body is between 30 and 90 feet. Drill strings in oil and gas production can extend as long as 20,000 feet, which means that as many as 700 sections of drill pipe and downhole tools can be used in the drill string. 
     There are several designs for the pin and box end of drill pipe. This invention is particularly useful for pin and box end designs that have a uniform diameter with the rest of the pipe component. Pipe component  20  has a uniform central bore or internal diameter  23 . Smaller pipe sizes and many other drilling components such as drill collars, heavy weight drill pipe, and jars may have a uniform internal diameter depending on the size of drill pipe used.  FIG. 1  also includes the overlapping slots made of a first slot  10  and a second slot  11 . The first slot  10  is smaller than the second slot  11 . 
     As shown in  FIG. 2 , an electrical transmission line or coaxial cable, of which conductive tube  24  is shown, can be placed within the internal diameter or central bore  23  of pipe component  20 . The electrical transmission line can be a coaxial cable including a conductive tube and conductive core with in it. Each end of the coaxial cable is placed near the end of each box end  22  and pin end  21 . 
       FIG. 3  is a more detailed close up of the coaxial cable in the pin end  21 , of which the conductive tube  24  is shown. The coaxial cable, of which the conductive tube  24  is shown, will have a first outer diameter  31  and a second outer diameter  30  which is larger than the first outer diameter  31 . The first slot  10  is smaller than the slot  11 . Slots  10  and  11  are made to overlap which are depicted more clearly in the other figures. The outer diameter  31  is smaller than the second slot  11 . The second slot  11  is at least as wide as the second outer diameter  30 . 
     As shown in  FIG. 4  we see a cross-sectional view of the pin end  21  form drill component  20  as depicted in FIG.  1 . Without the electrical transmission line or coaxial cable, of which conductive tube  24  is shown, in place, it is easier to see how the overlapping slots work. The first slot  10  intersects the second slot  11  such that an overlap of the slots occurs. The smaller width of slot  10  over laps the larger slot  11  such that an undercut  12  and shoulder  13  are created. The larger slot  11  is placed underneath the smaller slot  10  at the intersection of the two slots where the overlap exists. Slots  10  and  11  are formed such that both slots and the undercut  12  and shoulder  13  form complimentary recesses to the first and second outer diameters  30  and  31  of conductive tube  24  as depicted in FIG.  3 . In still another embodiment of the invention, the conductive tube  24  could be press fit into the complimentary recesses formed by the overlapping slots  10  and  11 . Furthermore the slots do not necessarily have to line up with each other; the slots could be offset by a desired amount depending on the type of electrical conductor being employed. 
     In another embodiment of the invention, more than two slots can be used. The invention can also include more than two shoulders as depicted in  FIG. 5  which is an enlarged view of the pin end  21  of drill component  20  as shown in  FIG. 1. A  first slot  10  and second slot  11  forms the undercut  12  and shoulder  13 . Another shoulder  14  is placed beyond slot  10 . This can be created by having third slot placed below slot  10 . Indeed, a plurality of slots can be implemented to increase the retention strength depending on the application as needed. Each subsequent slot should have an increasing width. Corresponding changes in the outer diameter of the conductive tube  24  would also need to be made such that the plurality of slots will form shoulders and undercuts that form complimentary recesses with each corresponding outer diameter of the conductive tube. 
       FIG. 6  is an enlarged cross-section of a pin end  21  of a drill component  20  depicting in greater detail the created shoulder  13  and undercut  12 . The length of overlap between first slot  10  and second slot  11  is within the elastic deformation range of the conductive tube. The conductive tube  24  is stretched in order to install it within the drill component and the overlapping slot. However, it cannot be stretched beyond the point where plastic deformation occurs. This aspect of the invention and the installation process will be discussed in greater detail below. 
     The distinctness of the overlapping slots and resulting undercuts and shoulders are best seen in  FIG. 7  which is an enlarged cross-section of the pin end  21  as depicted in FIG.  1 . The slot  10  has a smaller width than slot  11  as shown in FIG.  7 . The slot  11  goes under slot  10  at the point of intersection causing an overlap of the slots. Additionally, an undercut  12  is formed which holds the conductive tube  24  in place to a specified depth The relative height of each slot could be modified by raising or lowering the undercut to a desired depth for the electrical transmission line to be placed at. The shoulder  13  holds the larger outer diameter  30  of conductive tube  24  in place. Another shoulder  14  depicts the possibility of more than one shoulder used to retain the conductive tube of an electrical transmission line or coaxial cable providing the conductive tube has a corresponding outer diameter. 
     In the above descriptions and drawings only the pin end  21  of pipe component  20  has explicitly shown the retention mechanism of overlapping slots. Naturally, the same depiction could be made with the box end  22  of drill component  20  showing substantially the same overlapping slots with resulting undercut  12  and shoulder  13 . 
     A conductive tube  24  is placed within the slots  10  and  11 . Preferably, the conductive tube  24  runs almost the entire length of the drill component  20 , beginning in the pin end  21 , at overlapping slots  10  and  11 , passing through interior of the body or internal diameter  23  of the pipe component  20 , continuing through the box end  22 , and ending near the box end  22  in slots  10  and  11 . The conductive tube  71  is preferably held in tension after it is inserted in the drill pipe  20  and remains in tension during downhole use. This prevents the conductive tube  71  from moving relative to the undercut  12  and shoulder  13  during downhole use. The conductive tube is preferably made of metal, more preferably a strong metal, most preferably steel. By “strong metal” it is meant that the metal is relatively resistant to deformation in its normal use state. The metal is preferably stainless steel, most preferably  316  or  316 L stainless steel. A preferred supplier of stainless steel is Plymouth Tube, Salisbury, Md. 
     In a preferred embodiment of the invention, the conductive tube is held in place in each end by means of the overlapping slots  11  and  12 . The conductive tube  24  has a first outer diameter  31  and a second outer diameter  30  as shown in FIG.  3 . One end of the conductive tube  24  is placed in the overlapping slots  11  and  12  in drill component  20  by placing the larger outer diameter  30  in the larger slot  11 . The conductive tube  24  is then pulled such that the outer diameter  31  and  30  slide under the undercut  12  and the outer diameter  13  rests in slot  10  and outer diameter  30  rests in slot  11 . Subsequently the larger outer diameter  30  abuts against the shoulder  13 ; thus the conductive tube is held in place. 
     To complete the installation process in the opposite end of the drill component  20 , be it pin end  21  or box end  22 , the conductive tube  24  is stretched along the internal diameter  23  of drill component  20 . As the conductive tube  24  is stretched it increases in tension. The conductive tube is stretched far enough so that the larger outer diameter  30  will fit in the larger slot  11 . When this point is reached the conductive tube tension is relaxed causing the larger outer diameter  30  and smaller outer diameter  31  to slide under the undercut  12 . The conductive tube  24  will stop sliding when the larger outer diameter  30  abuts against the shoulder  13 . The conductive tube  24  should still be in tension so that each end of the conductive tube will remain place under the undercut  12  and abutting against the shoulder  13 . It is therefore necessary that the length of stretch needed to place the larger diameter  30  in larger slot  11  while in tension does not exceed the elastic deformation range of the conductive tube. If during the installation process the elastic deformation range is exceeded, the conductive tube  24  will lose its ability to rebound back to a shorter length. Thus the tube will not be in tension and will not stay attached to the drill component  20 . In a preferred embodiment, the conductive tube is in tension within the drill component. The preferred amount of tension is between 300 and 1200 pounds-force. In another embodiment, the conductive tube could be press fit into the smaller slot during the installation process described above. 
     In an alternative embodiment, the conductive tube may be insulated from the pipe in order to prevent possible galvanic corrosion. At present, the preferred material with which to insulate the conductive tube  71  is PEEK®. 
     Many types of data sources are important to management of a drilling operation. These include parameters such as hole temperature and pressure, salinity and pH of the drilling mud, magnetic declination and horizontal declination of the bottom-hole assembly, seismic look-ahead information about the surrounding formation, electrical resistivity of the formation, pore pressure of the formation, gamma ray characterization of the formation, and so forth. The high data rate provided by the present invention provides the opportunity for better use of this type of data and for the development of gathering and use of other types of data not presently available. 
     It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.