Abstract:
A threaded connection includes a pin member providing a single external thread comprising a first external portion and a second external portion, a box member providing a single internal thread comprising a first internal portion and a second internal portion, and a radial metal-to-metal seal to seal between the pin member and the box member, wherein the first and second internal portions threadably correspond with the first and second external portions, and wherein the first internal and external portions are characterized by a first wedge ratio and the second internal and external portions are characterized by a second wedge ratio, wherein the first wedge ratio is less than the second wedge ratio.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a Continuation-In-Part of U.S. patent application Ser. No. 11/026,512, filed on Dec. 30, 2004, hereby incorporated by reference in its entirety herein. 
     
    
     BACKGROUND OF INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention generally relates to wedge-threaded components of tubular connections. More particularly, the present invention relates to wedge-threaded components of tubular connections incorporating a metal-to-metal seal therebetween. More particularly still, the present invention relates to single-step multi-portion wedge-threaded tubular connections incorporating high-angle metal-to-metal seals.  
         [0004]     2. Background Art  
         [0005]     Casing joints, liners, and other oilfield tubulars are frequently used to drill, complete, and produce wells. For example, casing joints may be placed in a wellbore to stabilize and protect a formation against high wellbore pressures (e.g., wellbore pressures that exceed a formation pressure) that could otherwise damage the formation. Casing joints are sections of pipe (e.g., steel or titanium), which may be coupled in an end-to-end manner by threaded connections, welded connections, or any other connection mechanisms known in the art. As such, connections are usually designed so that at least one seal is formed between an interior of the coupled casing joints and the annulus formed between exterior walls of the casing joints and the interior walls of the wellbore (i.e., the formation). The seals may be elastomeric (e.g., an o-ring seal), thread seals, metal-to-metal seals, or any other seals known to one of ordinary skill in the art.  
         [0006]     It should be understood that certain terms are used herein as they would be conventionally understood, particularly where threaded tubular joints are connected in a vertical position along their central axes such as when making up a pipe string for lowering into a well bore. Typically, in a male-female threaded tubular connection, the male component of the connection is referred to as a “pin” member and the female component is called a “box” member. As used herein, “make-up” refers to engaging a pin member into a box member and threading the members together through torque and rotation. Further, the term “selected make-up” refers to the threading of a pin member and a box member together with a desired amount of torque or based on a relative position (axial or circumferential) of the pin member with respect to the box member. Furthermore, the term “box face” is understood to be the end of the box member facing outward from the box threads and the term “pin nose” is understood to be the end of the pin member facing outward from the threads of the connection. As such, upon make-up of a connection, the nose of the pin is stabbed or inserted into and past the face of the box.  
         [0007]     Referring to the geometry of threads, the term “load flank” designates the side wall surface of a thread that faces away from the outer end of the respective pin or box member on which the thread is formed and supports the weight (i.e., tensile load) of the lower tubular member hanging in the well bore. Similarly, the term “stab flank” designates the side wall surface of the thread that faces toward the outer end of the respective pin or box member and supports forces compressing the joints toward each other such as the weight of the upper tubular member during the initial make-up of the joint or such as a force applied to push a lower tubular member against the bottom of a bore hole (i.e., compressive force).  
         [0008]     One type of threaded connection commonly used oil country tubular goods is a wedge thread. Referring initially to  FIGS. 1A and 1B , a prior art tubular connection  100  having a wedge thread is shown. As used herein, “wedge threads” are threads, regardless of a particular thread form, that increase in width (i.e., axial distance between load flanks  225  and  226  and stab flanks  232  and  231 ) in opposite directions on a pin member  101  and a box member  102 . The rate at which the threads change in width along the connection is defined by a variable known as the “wedge ratio.” As used herein, “wedge ratio,” although technically not a ratio, refers to the difference between the stab flank lead and the load flank lead, which causes the width of the threads to vary along the connection. Furthermore, as used herein, a thread “lead” refers to the differential distance between a component of a thread on consecutive threads. As such, the “stab lead” is the distance between stab flanks of consecutive thread pitches along the axial length of the connection. A detailed discussion of wedge ratios is provided in U.S. Pat. No. 6,206,436, issued to Mallis, assigned to the assignee of the present invention, and incorporated by reference in its entirety herein. Furthermore, wedge threads are extensively disclosed in U.S. Pat. No. RE 30,647 issued to Blose, U.S. Pat. No. RE 34,467 issued to Reeves, U.S. Pat. No. 4,703,954 issued to Ortloff, and U.S. Pat. No. 5,454,605 issued to Mott, all assigned to the assignee of the present invention and incorporated herein by reference in their entirety.  
         [0009]     Referring still to  FIGS. 1A and 1B , a pin thread crest  222  in a wedge thread coupling is narrow towards a distal end  108  of pin member  101  while a box thread crest  291  is wide. Moving along an axis  105  (from right to left), pin thread crest  222  widens while box thread crest  291  narrows as it approaches a distal end  110  of box member  102 . As shown in  FIG. 1A , the threads are tapered, meaning that a pin thread  106  increases in diameter from beginning to end while a box thread  107  decreases in diameter in a complimentary manner. Having a thread taper may improve the ability to stab pin member  101  into box member  102  and distribute stress throughout the connection.  
         [0010]     Generally, thread seals are difficult to achieve in non-wedge (i.e., free-running) threads. However, thread forms that are unable to form a wedge seal in a free-running configuration may create thread seals when used in a wedge thread configuration. As should be understood by one of ordinary skill, as wedge threads do not require any particular type or geometry of thread form, a variety of thread forms may be used. One example of a suitable thread form is a semi-dovetailed thread form disclosed in U.S. Pat. No. 5,360,239, issued to Klementich and incorporated herein by reference in its entirety. Another thread form includes a multi-faceted load flank or stab flank, as disclosed in U.S. Pat. No. 6,722,706, issued to Church and incorporated herein by reference in its entirety. Each of the above thread forms is considered to be a “trapped” thread form, meaning that at least a portion of the corresponding load flanks and/or corresponding stab flanks axially overlap. An open (i.e., not trapped) thread form with a generally rectangular shape is disclosed in U.S. Pat. No. 6,578,880, issued to Watts and incorporated herein by reference in its entirety. As such, the above thread forms (i.e., those of Klementich, Church, and Watts) are examples of thread forms that may be used with embodiments of the invention. Generally, open thread forms such as buttress or stub are not suitable for wedge threads, as they would impart a large radial force on the box member. However, a generally square thread form, such as that disclosed by Watts, or a trapped thread form, may be used, as they do not impart an outward radial force on the box member. As such, those having ordinary skill in the art will appreciate that the teachings contained herein are not limited to particular thread forms.  
         [0011]     Referring again to  FIGS. 1A and 1B , in wedge threads, a thread seal may be accomplished through contact pressure caused by interference that occurs at make-up over at least a portion of connection  100  between pin load flank  226  and box load flank  225  and between pin stab flank  232  and box stab flank  231 . Close proximity or interference between roots  292  and  221  and crests  222  and  291  complete the thread seal when occurring proximate to such flank interference. Generally, higher pressures may be contained either by increasing interference between the roots and crests (“root/crest interference”) on pin member  101  and box member  102  or by increasing the aforementioned flank interference.  
         [0012]     Although various wedge thread connections exist having positive-stop torque shoulders (e.g., Klementich, referenced above), wedge threads typically do not have torque shoulders, so their make-up is “indeterminate,” and, as a result, the relative position of the pin member and box member may vary more during make-up for a given torque range to be applied than for connections having a positive-stop torque shoulder. For wedge threads designed to have flank interference and root/crest interference at a selected make-up, the connection is designed such that both the flank interference and root/crest interference increase as the connection is made-up (i.e. an increase in torque increases flank interference and root/crest interference). For tapered wedge threads having root/crest clearance, the clearance decreases as the connection is made-up. Regardless of the design of the wedge thread, corresponding flanks come closer to each other (i.e., clearance decreases or interference increases) during make-up. Indeterminate make-up allows for the flank interference and root/crest interference to be increased by increasing the make-up torque on the connection. Thus, a wedge thread may be able to thread-seal higher pressures of gas and/or liquid by designing the connection to have more flank interference and/or root/crest interference or by increasing the make-up torque on the connection. However, increased interference and make-up torque may increase stress on the connection during make-up, which may lead to premature failure of the connection.  
         [0013]     Furthermore, as shown, connection  100  includes a metal-to-metal seal  112  created by contact between corresponding seal surfaces  103  and  104 , respectively located on pin member  101  and box member  102 . Metal-to-metal seal  112  provides an additional measure of seal integrity (i.e., when a wedge thread seal is not sufficient) for threaded connection  100 , and is particularly useful where connection  100  is intended to contain high-pressure gases. While the metal-to-metal seal is shown located proximate to the distal end  108  of pin member  102 , it should be understood by one of ordinary skill in the art that metal-to-metal seal  112  may be positioned anywhere along the length of connection  100 , including, but not limited to, a location proximate to the distal end of box member  102 .  
         [0014]     Nonetheless, seal surfaces  103  and  104  of metal-to-metal seal  112  are usually constructed as corresponding frusta-conical surfaces characterized by a low angle (e.g., an angle less than about 4 or 5 degrees) of intersection with their corresponding remaining pin  101  and box  102  surfaces. Typically, low-angle metal-to-metal seal surfaces  103  and  104  are used in conjunction with wedge thread connections (e.g.,  100 ) because the indeterminate make-up thereof necessitates a seal capable of less precise axial alignment. As wedge threads make-up indeterminately, the relative axial position of pin member  101  and box member  102  will vary over successive make-up and breakout cycles. However, one disadvantage of a low-angle metal-to-metal seal is that seal surfaces  103  and  104  have friction contact areas than higher-angle seals, and as such, have less resistance to galling upon make-up. Furthermore, as low-angle metal-to-metal seals engage slowly (i.e., low radial displacement per revolution), the seals must be in contact for several revolutions. As such, in a wedge thread connection including a metal-to-metal seal, the seal is typically the first thing to “make-up,” such that the initial engagement of the seal marks the “hand tight” state of such a threaded connection. Therefore, while low-angle seals are beneficial in that they accommodate the indeterminate make-up characteristics of wedge threads, they may become ineffective over repeated make-up and break-out cycles as seal surfaces  103  and  104  are deformed and/or are cold-worked out of specification.  
         [0015]     In contrast, free-running threads used in oilfield tubular connections typically do not form thread seals when the connection is made-up. Referring now to  FIG. 2 , a prior art connection  200  having free-running threads is shown. The free-running threads include load flanks  254  and  255 , stab flanks  257  and  258 , crests  259  and  262 , and roots  260  and  261 . As is typical of a connection with free-running threads, connection  200  relies on a positive-stop torque shoulder formed by the contact of surfaces  252  and  251  disposed on a pin member  201  and a box member  202 , respectively. The positive-stop torque shoulder shown in  FIG. 2  is commonly referred to as a “pin nose shoulder.” In other connections, the positive-stop torque shoulder may instead be formed by a box face  263  and a mating shoulder (not shown) on pin member  201 . The positive-stop torque shoulder also provides a seal. Unlike wedge threads (e.g., those shown in  FIG. 1B ), which make-up by the wedging of the pin thread  106  and the box thread  107 , free-running threads rely on the positive-stop torque shoulder to load connection  200  during make-up. To make-up connection  200 , pin member  201  and box member  202  are screwed together until surfaces  251  and  252  are brought into abutment, at which point pin load flank  254  and box load flank  255  are also in abutment. Additional torque is applied to pin member  201  and box member  202  to load surfaces  252  and  251  and pin load flank  254  and box load flank  255  until the desired amount of make-up torque (i.e., the selected make-up) has been applied to connection  200 .  
         [0016]     Because a large gap  253  exists between pin stab flank  257  and box stab flank  258 , connection  200  does not accomplish a thread seal. Gap  253  occurs as a result of how free-running threads with positive-stop torque shoulders are loaded. Applying torque to connection  200  during make-up against the positive-stop torque shoulder causes pin member  201  to be compressed while box member  202  is stretched in tension. Note that when a box face shoulder is used, box member  202  is compressed while pin member  201  is stretched in tension. The force between pin member  201  and box member  202  is applied through pin load flank  254  and box load flank  255 . Notably pin stab flank  257  and box stab flank  258  are not loaded during make-up. This results in contact pressure between load flanks  254  and  255  and gap  253  between stab flanks  257  and  258 . As discussed above, a wedge thread (e.g.,  FIG. 1 ) forms a thread seal in part because of the interference between load flanks  225  and  226  and stab flanks  232  and  231 . In wedge threads, this occurs near the end of the make-up of the connection because of the varying width of pin thread  106  and box thread  107 . To have similar interference between load flanks  254  and  255  and stab flanks  257  and  258  on a cylindrical (i.e., non-tapered) free-running thread, the interference would exist substantially throughout the make-up of the connection because pin thread  206  and box thread  207  have a continuous width. Furthermore, root/crest interference, if any, would exist substantially throughout the make-up of the connection. This could lead to galling of the threads and difficulty in making-up the connection.  
         [0017]     The variance in thread width for a wedge thread occurs as a result of the load flanks having different leads than the stab flanks. A thread lead may be quantified in inches per revolution or by the commonly used inverse term “thread pitch,” (i.e., threads per inch). A graph of the leads for a prior art wedge thread is shown in  FIG. 3A . For this connection, the load lead  14  is constant over the length of the connection and greater than the stab lead  12 , which is also constant. The nominal lead is shown as item  10 . As used herein, “nominal lead” refers to the average of load lead  14  and stab lead  12 . The thread will widen with each revolution by the difference in load lead  14  and stab lead  12 . As described above, the difference in the load lead  14  and the stab lead  12  is the “wedge ratio.” For a free-running thread (i.e., non-wedge thread), load lead  14  and stab lead  12  would be substantially equal, thus causing the free-running thread to have a substantially constant thread width (i.e., a zero wedge ratio).  
         [0018]     Intentional variances in thread leads have been disclosed in the prior art for the purposes of load distribution. One example of a varied thread lead for stress distribution is disclosed in U.S. Pat. No. 4,582,348 issued to Dearden, hereby incorporated by reference in its entirety. Dearden discloses a connection with free-running threads that has the pin thread and box thread divided into three sections, each with different leads (note that Dearden refers to thread pitch, which is quantified as threads per inch). In  FIG. 3B , a graph of the thread leads for the box member and the pin member of Dearden is shown. As shown in the graph, at one end of the connection, a pin thread lead  21  is larger than the box thread lead  22 . In the intermediate section  23 , the pin thread lead  21  and box thread lead  22  are substantially equal. Then, at the other end of the connection, box thread lead  22  is larger than pin thread lead  21 . In Dearden, the changes in pin thread lead  21  and box thread lead  22  are step changes (i.e., substantially instantaneous changes in the lead). The varied thread leads disclosed by Dearden are intended to distribute loading across a greater portion of the connection, and have no effect on the ability of the free-running threads to form a thread seal. Dearden does not disclose varying a load lead or stab lead independent of one another.  
         [0019]     Another connection is disclosed in U.S. Pat. No. 6,976,711, issued to Sivley, assigned to the assignee of the present invention, and hereby incorporated by reference in its entirety. Sivicy discloses connections having a variance in load lead and/or stab lead on one or both of the pin member and the box member. A graph of an embodiment disclosed by Sivley is shown in  FIG. 3C . Sivley discloses varying load lead  14  relative to stab lead  12  at a selected rate over at least a portion of the pin thread and/or box thread. In  FIG. 3C , the connection is a wedge thread as shown by the difference between load lead  14  and stab lead  12 . Load lead  14  and stab lead  12  converge at a linear rate towards the end of the thread. Sivley discloses various other embodiments having load leads  14  and stab leads  12  that vary at linear rates relative to each other. The variance in the thread leads distributes the loads experienced by the connection over the length of the connection.  
         [0020]     Referring now to  FIG. 4 , a prior art two-step connection is shown. The threads that form the connection are separated across multiple “steps,” a large step, indicated by a bracket  31 , and a small step, indicated by a bracket  32 . The portion between large step  31  and small step  32  is commonly referred to as a mid-step  33 . In some connections, mid-step  33  may be used as a metal-to-metal seal. Preferably, a pin thread crest (often referred to as a major diameter in a non-tapered threaded connection) on small step  32  of pin member  401 , at its full design height, does not interfere with a box thread crest (often referred to as a minor diameter in a non-tapered threaded connection) on large step  31  of box member  402  when pin member  401  is stabbed into box member  402 . The diameter of small step  32  of pin member  401  is smaller than the smallest crest-to-crest thread diameter on large step  31  of box member  402  so a pin thread  406  on small step  32  may be stabbed past a box thread  407  on large step  31 . The threads on both small step  32  and large step  31 , which have substantially the same nominal lead, engage with each revolution to make-up the connection. Thus, the number of revolutions during which the threads slide or rub against each other is reduced for the same number of engaged threads. A multi-step connection allows for each of the steps to have threads with different characteristics as long there is little or no variance in the nominal lead of the threads on the steps.  
         [0021]     A two-step wedge thread connection is disclosed in U.S. Pat. No. 6,206,436, issued to Mallis, and hereby incorporated by reference herein. Mallis discloses a two-step wedge thread connection having different wedge ratios, one of which is considered to be an aggressive wedge ratio and the other a conservative wedge ratio, wherein “aggressive” refers to a larger wedge ratio, and “conservative” refers to a smaller wedge ratio. With all other thread characteristics held constant, a greater wedge ratio will exhibit a more determinate make-up. However, too large of a wedge ratio may have an inadequate wedging effect, which may allow the connection to back off during use. Conversely, smaller wedge ratios are better able to resist backing-off of the connection, but may have such an indeterminate make-up that galling may occur over the lengthened make-up distance. Mallis discloses that one of the steps in a multi-step thread may have a wedge ratio optimized for a more determinate make-up (aggressive), while another step may have a wedge ratio optimized to prevent backing-off of the connection (conservative).  
         [0022]     U.S. Pat. Nos. 6,174,001 and 6,270,127 issued to Enderle, assigned to the assignee of the present invention, and incorporated by reference herein, disclose two-step, low torque wedge threads for tubular connections. In the references, one step is provided so that there is interference at make-up along at least one of the complementary stab flanks, load flanks, roots, and crests while clearance is provided along another step along at least one of the complementary stab flanks, load flanks, roots, and/or crests.  
         [0023]     This configuration reduces the amount of torque required for make-up of the connection while retaining torque sensitivity, sealing capability, and threads necessary for structural purposes.  
         [0024]     One problem with two-step connections is that the connection must be thick to reach  100  percent pipe body efficiency. As used herein, “pipe body efficiency” is the tensile strength of the connection relative to the tensile strength of the tubular. The primary reason for needing a thicker connection is the unengaged space of the mid-step, which is required so that the threads on the large step may clear the threads on the small step during stabbing. The mid-step, due to the lack of thread engagement, does not contribute to the overall strength of the connection. The advantages of having two separate threads often makes up for the decreased pipe body efficiency, however, it is desirable to have a single-step thread that may exhibit the advantages of two-step connections.  
       SUMMARY OF INVENTION  
       [0025]     In one aspect, the present invention relates to a threaded connection including a pin member providing a single external wedge thread having a first external portion and a second external portion. Further, the threaded connection includes a box member providing a single internal wedge thread having a first internal portion and a second internal portion, wherein the first and second internal portions threadably correspond with the first and second external portions. Furthermore, the first internal and external portions are preferably characterized by a first wedge ratio and the second internal and external portions are preferably characterized by a second wedge ratio, wherein the first wedge ratio is less than the second wedge ratio and a radial metal-to-metal seal seals between the pin member and the box member and wherein the radial metal-to-metal seal comprises a seal angle between about 4 degrees and about 15 degrees.  
         [0026]     In another aspect, the present invention relates to a threaded connection having a pin member providing a single external wedge thread comprising a first external portion and a second external portion. Further, the threaded connection has a box member providing a single internal wedge thread comprising a first internal portion and a second internal portion, wherein the first and second internal portions threadably correspond with the first and second external portions. Furthermore, the first internal and external portions are preferably characterized by a first wedge ratio and the second internal and external portions are preferably characterized by a second wedge ratio. Further still, a radial metal-to-metal seal seals between the pin member and the box member, and the pin and box members are configured such that, during make-up, the first external and internal portions reach a first specified make-up before engagement of the radial metal-to-metal seal and a second specified make-up of the second external and internal portions.  
         [0027]     In another aspect, the present invention relates to a method to couple a threaded connection including engaging a pin end of the connection into a box end of the connection, wherein the pin end comprises an external wedge thread and the box end comprises an internal wedge thread. Further, the method includes rotating the connection to a first position to make-up a first portion of the pin end wedge thread with a first portion of the box end wedge thread at a first wedge ratio and rotating the connection to a second position to engage a radial metal-to-metal seal of the threaded connection. Further still, the method includes rotating the connection to a third position to make-up a second portion of the pin end wedge thread and a second portion of the box end wedge thread at a second wedge ratio.  
         [0028]     In another aspect, the present invention relates to a threaded connection having wedge threads, the threaded connection includes a pin member comprising a pin thread having a pin thread crest, a pin thread root, a pin load flank, and a pin stab flank, wherein the pin thread comprises at least a first portion, a transition region, and a second portion formed sequentially thereon. Further, the threaded connection includes a box member comprising a box thread having a box thread crest, a box thread root, a box load flank, and a box stab flank, wherein the box thread comprises at least a first portion, a transition region, and a second portion formed sequentially thereon, the portions on the box thread corresponding generally in axial position with the portions on the pin thread. Preferably, the first portion has a first wedge ratio, the transition region has a transition wedge ratio, and the second portion has a second wedge ratio, wherein thread leads are substantially constant within each of the portions. Furthermore, the threaded connection includes a radial metal-to-metal seal to seal between the pin member and the box member, wherein the pin and box members are configured such that during make-up, the first portions reach a first specified make-up before engagement of the radial metal-to-metal seal and a second specified make-up of the second portions. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0029]      FIGS. 1A and 11B  depict cross-sectional views of a prior art tubular connection having wedge threads.  
         [0030]      FIG. 2  is a cross-sectional view of a prior art tubular connection having free-running threads.  
         [0031]      FIGS. 3A, 3B , and  3 C show graphical representations of thread leads for various prior art tubular connections.  
         [0032]      FIG. 4  is a cross-sectional view of a prior-art two-step tubular connection having free-running threads.  
         [0033]      FIGS. 5A, 5B , and  5 C schematically depict a two-portion wedge threaded connection.  
         [0034]      FIGS. 6A, 6B , and  6 C schematically depict a two-portion wedge threaded connection.  
         [0035]      FIGS. 7A and 7B  schematically depict a two-portion wedge threaded connection.  
     
    
     DETAILED DESCRIPTION  
       [0036]     Some embodiments of the present invention include single-step wedge-threaded connections having variances in the wedge ratio so that a high-angle metal-to-metal seal may be used therewith. Furthermore, some embodiments are characterized by a multiple stage make-up of a wedge threaded connection, such that a first portion of the wedge thread may make-up at a conservative wedge ratio before a metal-to-metal seal engages and before a second portion of the wedge thread makes-up at an aggressive wedge ratio. Further still, in some embodiments, the metal-to-metal seal may engage simultaneously with the second portion make-up while, in other embodiments, the metal-to-metal seal may engage prior to the second portion make-up.  
         [0037]     Referring now to  FIGS. 5A-5C , a three-portion wedge-threaded connection  500  is shown. Particularly,  FIG. 5A  depicts connection  500  schematically as having a pin threaded member  506  and a box threaded member  507 . Next,  FIG. 5B  is a graphical representation of the box thread lead of box member  507 . Furthermore,  FIG. 5C  is a graphical representation of the pin thread lead of pin member  506 . As such,  FIGS. 5B and 5C  depict their respective thread lead length (e.g., in inches) as a function of axial position (e.g., the thread number).  
         [0038]     Nonetheless, for the sake of clarity, connection  500  is shown in  FIG. 5A  partially made-up, rather than at a selected final make-up. Referring to  FIG. 5A , pin threaded member  506  corresponding to the graph of  FIG. 5C  is shown partially made-up with a box threaded member  507  corresponding to the graph shown in  FIG. 5B . The partially made-up thread shown in  FIG. 5A  has three thread portions,  501 A,  503 , and  501 B. Thread portion  503  is defined by the distal ends of box thread portion  503 A and pin thread portion  503 B, as shown in  FIGS. 5B and 5C , when the box and pin are partially made-up.  
         [0039]     Referring now to  FIGS. 5B and 5C , the lengths of various thread leads as a function of axial position are depicted, wherein each unit of the axial position axis represents about a 360 degree turn of a thread pitch. For example, thread portions  501 A and  501 B are about seven thread pitches each, while another thread portion  503  is about one thread pitch. In  FIG. 5A , pin thread  506  includes pin stab flanks  531  and pin load flanks  526  and box thread  507  includes box stab flanks  532  and box load flanks  525 . Both pin and box threads are divided into three thread portions,  501 A,  503 A, and  501 B. While wedge-thread connection  500  is shown as a three-portion connection, it should be understood that other configurations (e.g., two or greater than three portions) may be used to create wedge-threaded connections in accordance with embodiments of the present invention.  
         [0040]     Referring still to  FIGS. 5B and 5C , thread portions  501 A have a wedge ratio  51 A and thread portions  501 B have a wedge ratio  511 B, wherein wedge ratios  511 A and  511 B are substantially the same. Thread portion  503 A of box member  507  and pin member  506  exhibit a wedge ratio  513  larger than wedge ratios  511 A and  511 B. As shown, box thread portion  503 A and pin thread portion  503 B are the same axial length, but as will be demonstrated later, thread portions  503 A and  503 B may be of different axial lengths. As thread portions  501 A and  501 B may have the same characteristics, together, they may be considered as a single, discontinuous thread  501 , which is “interrupted” or “perturbed” by thread portions  503 A and  503 B.  
         [0041]     Since a load lead  514  and a stab lead  516  are varied in a complementary manner on both pin member  506  and box member  507 , a nominal lead  510  is substantially constant over the length of both pin member  506  and box member  507 . At the end of first thread portion  501 A, wedge ratio  511 SA increases to a second wedge ratio  513  by increasing a load lead  514  while proportionally decreasing a stab lead  516 , so that nominal lead  510  is maintained substantially constant. As mentioned earlier, second wedge ratio  513  is larger than both wedge ratio  511 A of thread portion  501 A and wedge ratio  511 B of thread portion  501 B. Furthermore, in some embodiments, a helical length of made-up thread portion  503  may be in increments of about  360  degrees to prevent eccentric loading of connection  500 . After portion  503 , wedge ratio  513  decreases to wedge ratio  511 B characteristic of thread portion  501 B, which, as shown in  FIGS. 5A-5C , is substantially equal to wedge ratio  511 A of thread portion  501 A.  
         [0042]     At the partially made-up condition shown in  FIG. 5A , there may be contact between the pin stab flank  531  and box stab flank  532 , and between pin load flank  526  and box load flank  525  in both thread portion  500 A and thread portion  501 B, but clearance  504  between the stab and load flanks in made-up thread portion  503 .  
         [0043]     Additionally,  FIGS. 5B-5C  disclose an offset  505  between the start of thread portion  503 B on pin thread  506  ( FIG. 5C ) and the start of thread segment  503 A on box thread  507  ( FIG. 5B ). As shown, thread portion  503 A begins at a slightly earlier selected axial position on box member  507  than thread portion  503 B on pin member  506 .  
         [0044]     This offset allows the threads of box member  507  to “open up” or widen slightly earlier than pin thread  506 , resulting in a clearance between flanks in thread portion  503  when the connection is partially made-up as shown in  FIG. 5A . To return to flank contact (or interference), thread portion  501 B may begin at an earlier axial position on box member  507 , thus allowing threads of pin member  506  to “catch up.” Thus, the size of offset  505  may dictate the relative flank contact in thread segments  501 A,  503 , and  501 B. For example, assuming connection  500  shown in  FIGS. 5A-5C  (wherein, at a selected partial make-up, the thread flanks in thread portions  501 A and  501 B are in contact and the thread flanks in thread portion  505  are in clearance), increasing offset  505  without changing any other thread characteristics would increase the flank clearance in thread portion  503  and reduce or eliminate the flank contact in thread portion  501 B.  
         [0045]     Similarly, relative flank contact in thread segments  501 A,  503 , and  501 B at a selected make-up may be changed by altering the relative axial lengths of box thread portion  503 A and pin thread portion  503 B. For example, assuming connection  500  shown in  FIGS. 5A-5C , increasing the axial length of pin thread portion  503 B in  FIG. 5C  would result in increased contact stress in thread portion  501 B, reduced contact stress in thread portion  501 A, and an increased clearance at thread portion  503 . Therefore, connection  500  would tend to make-up first on the flanks of thread portion  501 B.  
         [0046]     By varying the size of offset  505  and the relative widths of thread portions  503 A and  503 B on the box and pin threads respectively, a thread designer may tailor the relationship between the flanks in all three thread portions  501 A,  503 , and  501 B at a selected final make-up. For example, in one embodiment, the thread flanks in at least one of the three thread portions  50 A,  503 , and  501 B may be in clearance at a selected make-up. Similarly, in other embodiments the flank interference in thread portion  503  at a selected final make-up may be less than, equal to, or greater than the flank interference in thread portions  501 A or  501 B. In another embodiment, there may be flank interferences in all thread portions  501 A,  503 , and  500 B at a selected make-up which are all different from one another. In such an embodiment, flank contact may occur on one thread portion of the wedge thread before another thread portion at a preliminary make-up, but with both portions having flank interference at a selected make-up. Further, one or more thread portions may have interference between only the load flanks or the stab flanks instead of both.  
         [0047]     Because wedge ratios  51 IA and  511 B are conservative relative to wedge ratio  513  of portion  503 , contact stress between mating flanks in thread portions  501 A and  501 B will rise slowly with increased make-up, while the flank contact stresses in portion  503  will rise more quickly. In the embodiment represented by  FIGS. 5A-5C , at a partial make-up, the flanks of thread portions  501 A and  501 B may be in contact while the flanks of thread portion  503  may be in clearance. Subsequently, at a selected final make-up, the flank interference may be the same in all three thread portions  501 A,  503 , and  501 B.  
         [0048]     In another embodiment, at a selected final make-up the flank interference in thread portions  501 A and  503  may be the same while the flank interference in thread portion  501 B may be lower. This embodiment may be useful, for example, in high-torque applications where thread portion  501 B, having a lower flank interference at a selected final make-up, may act as a “back-up” torque shoulder.  
         [0049]     Referring now to  FIGS. 6A-6C , a three-portion wedge-threaded connection  600  is shown. In  FIG. 6A , a pin member  606  corresponding to the graph of  FIG. 6C  is shown at a selected final make-up with a box member  607  corresponding to the graph of  FIG. 6B . In this embodiment, threads of pin member  606  and box member  607  exhibit interference between load flanks  625  and  626  and stab flanks  631  and  632  on a first portion  601  and a second portion  603 , on both a first portion  601  (analogous to the small step  32  of  FIG. 4 ) and a second portion  603  (analogous to the large step  31  of  FIG. 4 ) of the wedge-threaded connection  600  at selected make-up. Furthermore, a transition region  602  between first portion  601  and second portion  603  is shown. Thus,  FIGS. 6A-6C  represent a first portion  601  of approximately seven thread pitches, a transition region  602  of approximately one pitch, and a second portion  603  of approximately seven pitches.  
         [0050]     In contrast, two-step connections having differential wedge ratios are disclosed in U.S. Pat. No. 6,206,436 issued to Mallis, discussed above. Mallis&#39; teachings (including all of the advantages), as they apply to two-step connections having two different wedge ratios, are generally applicable to the multiple thread-portion single step connections disclosed herein. Using terminology from Mallis, in the embodiment shown in  FIGS. 6A-6C , second portion  603  exhibits an “aggressive” wedge ratio  613 , while first portion  601  exhibits a “conservative” wedge ratio  611 . However, unlike the disclosure of Mallis and FIGS.  5 A-C discussed above,  FIGS. 6A-6C  depict continuous, single-step threads without interruptions between portions.  
         [0051]     While transition region  602  is shown having clearance between load flanks  625 ,  626  and stab flanks  631 ,  632 , it should be understood by one of ordinary skill that transition region  602  may have load flank  625 ,  626  or stab flank  631 ,  621  interference. Furthermore, while transition region  602  is shown as extending over only one thread pitch, it should be understood that a larger or smaller transition region  602  may be used. Additionally, in one embodiment, flank interference may occur on one portion of the wedge thread before the other at make-up, with both first portion  601  and second portion  603  having interference at selected make-up. Further, one or more of thread portions  601 ,  602 , and  603  may have interference between only the load flanks or the stab flanks instead of both.  
         [0052]     To achieve the three-portion configuration shown in  FIG. 6A , a load lead  614  and a stab lead  616  may be varied in a complementary manner on both pin member  606  and box member  607  as shown in  FIGS. 6B and 6C . As depicted, the nominal lead  610  is held substantially constant over the length threads on of both pin member  606  and box member  607 . Along first portion  601 , the difference between load lead  614  and stab lead  616  (i.e., the wedge ratio  611 ) is substantially constant. At the end of first portion  601 , wedge ratio  611  increases to a transition wedge ratio  612  by increasing load lead  614  a selected amount while proportionally decreasing stab lead  616 , substantially maintaining nominal lead  610 . As may be seen, transition wedge ratio  612  is larger than both wedge ratio  611  of first portion  601  and wedge ratio  613  of second portion  603 . The length of the threads at transition region  602  allows transition between first portion  601  and second portion  603 , and is relatively small in helical length compared to first portion  601  and second portion  603 . In some embodiments, the helical length of transition region  602  may be in increments of about  360  degrees to prevent eccentric loading of the connection. Following transition region  602 , transition wedge ratio  612  decreases to wedge ratio  613  characteristic of second portion  603 , which, in  FIGS. 6A-6C , is shown greater than wedge ratio  611  of first portion  601 .  
         [0053]     Additionally,  FIGS. 6A-6C  also disclose an offset  605  in transition thread portion  602  of pin member  606  and box member  607 . As shown, transition thread portion  602  begins at a slightly earlier selected axial position on box member  607  than on pin member  606 . This offset allows the threads of box member  607  to “open up” or widen slightly earlier than those of pin member  606 , resulting in a selected clearance between flanks on the transition region  602 . To return to flank interference, second portion  603  may begin at an earlier selected axial position on box member  607 , thus allowing threads of pin member  606  to “catch up.” Alternatively, second portion  603  of box member  607  and pin member  606  of may begin simultaneously to further delay a selected make-up of second portion  603  following a selected make-up of first portion  601 . Thus, variations in load lead  614  and stab lead  616  over the length of the threads allows for a connection to exhibit different make-up characteristics in each portion of the connection. Those having ordinary skill in the art will appreciate that various combinations of portions (e.g,  601 ,  602 ,  603 ) may be used in accordance with embodiments of the present invention.  
         [0054]     Referring now to  FIGS. 7A-7B , a two-portion wedge-threaded connection  700  is shown schematically. Connection  700  is distinct from connection  600  of  FIGS. 6A-6B  in that connection  700  does not include a transition thread portion (e.g.,  602 ) between a first portion  701  and a second portion  703 . As such, connection  700  is characterized by a wedge ratio  711  of first portion  701  that instantaneously expands to a larger wedge ratio  713  of second portion  703 . Similar to the connections shown in  FIGS. 5 and 6 , the second portion of the pin thread may lag the box thread lead by an offset  705  to allow the box thread to open up or widen slightly earlier than pin thread. While change in wedge ratio from  711  to  713  is shown as a substantially instantaneous step change, a smoother graduated change may be used.  
         [0055]     As described above, wedge threads are characterized by indeterminate make-up. However, the amount of indeterminateness of a wedge-threaded connection may be varied by changing the underlying wedge ratio. For example, wedge-threaded connections having a more conservative (i.e., lower) wedge ratio, make-up to a selected amount of flank interference more indeterminately than those having more aggressive wedge ratios. As such, a connection having a more conservative wedge ratio will require more rotation (and torque) to reach a selected make-up, and thus be more indeterminate than a connection having an aggressive wedge ratio. In contrast, connections exhibiting more aggressive wedge ratios will make-up more determinately, but will be less resistant to backing off than connections having conservative wedge ratios.  
         [0056]     As such, single-step wedge-threaded connections with at least two threaded portions at differing wedge ratios are highly beneficial in connections having a metal-to-metal seal (e.g.,  103  and  104  of  FIG. 1A ) to reduce the amount of wear and galling experienced by such seals. Particularly, a continuous, wedge-threaded connection, in which a first thread portion has a conservative wedge thread, and a second thread portion has an aggressive wedge thread, may be used to allow a more determinate engagement of such a seal.  
         [0057]     For example, in an embodiment in accordance with the present invention, a continuous, single-step wedge-threaded connection may be constructed having two (or more) portions, a first portion having a conventional (less aggressive) wedge ratio, and a second portion having a higher (more aggressive) wedge ratio. Because of the high wedge ratio of the second portion, the connection could include a radial metal-to-metal seal having a seal angle between about 4 and about 15 degrees. Further, in some embodiments, seal angles of about 7 degrees, about 14 degrees, or anywhere therebetween may be used. As described above, the metal-to-metal seal may be a pin-nose seal, box face seal, or any other seal known to one of ordinary skill in the art.  
         [0058]     Furthermore, for a two-portion wedge-threaded connection, the more aggressive second portion may comprise a smaller percentage of the total number of thread pitches than the more conservative first portion. For example, if a conventional standard wedge thread has ten pitches and a wedge ratio of 0.015″/pitch (i.e., the thread width grows by  10  pitches·0.015″/pitch=0.150″ over the length of the thread), a two-portion wedge thread of the same axial length may have two pitches at a wedge ratio of 0.030 in the second portion and the remaining eight pitches at 0.01125″/pitch wedge ratio (i.e., [0.150″−2·0.030″]/8) in the first portion and still maintain the same growth in thread width over the length of the thread. Alternatively, the first and second portions may be of substantially equal number of pitches or length. Alternatively still, a multi-portion wedge-threaded connection may have several alternating conservative and aggressive portions, wherein each conservative/aggressive couple acts to selectively make-up the connection in parallel.  
         [0059]     The make-up sequence for a continuous two-portion wedge-threaded connection in accordance with embodiments of the present invention may include the first portion making-up (e.g., a preliminary rotation) before the engagement of the metal-to-metal seal (e g, a secondary rotation) and the making-up of the second portion (e.g., a tertiary rotation). Preferably, the wedge ratio of the second portion could be related to the angle of the metal-to-metal seal, such that the second portion reaches its selected make-up at the same time the metal-to-metal seal becomes fully engaged. Generally, to achieve this goal, a steeper seal angle will require a higher wedge ratio in the second thread portion. For example, as the metal-to-metal seal having a seal angle of about  14  degrees will fully engage within ¼ turn of a typical wedge thread, the axial position and wedge ratio of the second portion may be chosen such that the second portion reaches desired flank interference in about ¼ turn, at essentially the same selected make-up that the metal-to-metal seal reaches full engagement.  
         [0060]     It should be understood that wedge thread connections in accordance with embodiments of the present invention are advantageous over those in the prior art in that the metal-to-metal seals contained therewith may be more durable and less susceptible to damage in service and during make-up and break-out cycles.  
         [0061]     High-angle metal-to-metal seals in accordance with embodiments of the present invention are less susceptible to damage from eccentric contact during make-up and break-out as they are engaged after a first portion of a continuous multi-portioned wedge-threaded connection is made up. As such, make-up of the first portion prior to the engagement of the metal-to-metal seals may act to “pilot” the seal components into engagement with reduced likelihood of eccentric contact. Similarly, during break out, the seals may be disengaged prior to break-out of the first portion, thus again allowing the first portion to “pilot” the seal components apart axially, thus protecting seal surfaces from eccentric contact. Thus early engagement/late disengagement of the first portion of a continuous multi-portioned wedge-threaded connection may protect seal surfaces by piloting components of a metal-to-metal seal into and out of engagement along the an axis of the connection.  
         [0062]     Furthermore, as described above, the reduced contact area of a high-angle seal in accordance with embodiments of the present invention translates to less metal-to-metal seal area, thereby reducing the likelihood and magnitude of galling therebetween. Furthermore, as the high-angle seals engage under less rotational displacement than low-angle seals, there is less metal-to-metal frictional displacement through that seal area.  
         [0063]     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.