Embodiments of the present invention generally relate to an apparatus for supporting a tubular that more evenly distributes stress along the contact length of a tubular than prior art designs. In one embodiment, an apparatus for supporting a tubular is provided. The apparatus includes a bowl having a longitudinal opening extending therethrough and an inner surface for receiving a gripping member. The gripping member is movable along the surface of the bowl for engaging the tubular. The apparatus is configured so that an upper portion of the gripping member will engage the tubular before the rest of the gripping member engages the tubular.

CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims benefit of U.S. Provisional Patent Application No. 60/680,204 (Atty. Dock. No. WEAT/0647L), filed May 12, 2005, and U.S. Provisional Patent Application No. 60/689,199 (Atty. Dock. No. WEAT/0647L02), filed Jun. 9, 2005. The above-referenced Applications are hereby incorporated by reference.  
         [0002]     U.S. patent application Ser. No. 10/207,542 (Atty. Docket No. WEAT/0239, entitled “FLUSH MOUNTED SPIDER”), filed Jul. 29, 2002 is hereby incorporated by reference.  
         [0003]     U.S. patent application Ser. No. 10/625,840 (Atty. Docket No. WEAT/0116.C1, entitled “APPARATUS AND METHODS FOR TUBULAR MAKEUP INTERLOCK”), filed Jul. 23, 2003, is herein incorporated by reference.  
         [0004]     U.S. patent application Ser. No. 10/794,797 (Atty. Docket No. WEAT/0371, entitled “METHOD AND APPARATUS FOR DRILLING WITH CASING”), filed Mar. 5, 2004, is herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0005]     1. Field of the Invention  
         [0006]     Embodiments of the present invention generally relate to an apparatus for supporting a tubular.  
         [0007]     2. Description of the Related Art  
         [0008]     The handling and supporting of tubular pipe strings has traditionally been performed with the aid of a wedge shaped members known as slips. In some instances, these members operate in an assembly known as an elevator or a spider. Typically, an elevator or a spider includes a plurality of slips circumferentially surrounding the exterior of the pipe string. The slips are housed in what is commonly referred to as a “bowl”. The bowl is regarded to be the surfaces on the inner bore of the spider, an elevator, or another tubular-supporting device. The inner sides of the slips usually carry teeth formed on hard metal dies for engaging the pipe string. The exterior surface of the slips and the interior surface of the bowl have opposing engaging surfaces which are inclined and downwardly converging. The inclined surfaces allow the slip to move vertically and radially relative to the bowl. In effect, the inclined surfaces serve as wedging surfaces for engaging the slip with the pipe. Thus, when the weight of the pipe is transferred to the slips, the slips will move downward with respect to the bowl. As the slips move downward along the inclined surfaces, the inclined surfaces urge the slips to move radially inward to engage the pipe. In this respect, this feature of the spider is referred to as “self tightening.” Further, the slips are designed to prohibit release of the pipe string until the pipe load is supported and lifted by another device.  
         [0009]     In the makeup or breakup of pipe strings, the spider is typically used for securing the pipe string in the wellbore at a rig floor. Additionally, an elevator suspended from a rig hook includes a separately operable set of slips and is used in tandem with the spider. The elevator may include a self-tightening feature similar to the one in the spider. In operation, the spider holds the tubular string at an axial position while the elevator positions a new pipe section above the pipe string for connection. After completing the connection, the elevator pulls up on and bears the weight of the string thereby releasing the pipe string from the slips of the spider therebelow. The elevator then lowers the pipe string into the wellbore. Before the pipe string is released from the elevator, the spider is allowed to engage the pipe string again to support the pipe string. After the weight of the pipe string is switched back to the spider, the elevator releases the pipe string and continues the makeup or break out process for the next joint.  
         [0010]     Slips are also historically used in a wellbore to retain the weight of tubular strings and aid in locating and fixing tubular strings at a predetermined location in a wellbore. Packers, liner hangers and plugs all use slips and cones, the cones providing an angled surface for the slip members to become wedged between a wellbore wall and the tubular string and ensuring that the weight of the string is supported.  
         [0011]     New oil discoveries require drilling deeper wells, which means that spiders and elevators must support heavier pipe strings without crushing the pipe. This slip-crushing issue limits the length of the pipe string that can be suspended by the slips. Uneven axial distribution of the radial slip load on a pipe string exacerbates the slip crushing issue. Therefore, there exists a need in the art for a slip assembly or a spider which more evenly distributes the stress on a tubular along the contact length of the tubular.  
       SUMMARY OF THE INVENTION  
       [0012]     Embodiments of the present invention generally relate to an apparatus for supporting a tubular that more evenly distributes stress along the contact length of a tubular than prior art designs. In one embodiment, an apparatus for supporting a tubular is provided. The apparatus includes a slip member movable along a supporting surface in order to wedge the slip member between the tubular to be retained and the supporting surface. The contact surface between the slip member and the supporting surface is designed whereby an upper portion of the gripping surface of the slip member will initially contact the tubular, thereby distributing the forces generated by the weight of the tubular in a more effective manner.  
         [0013]     In another embodiment, an apparatus for supporting a tubular is provided. The apparatus includes a bowl having a longitudinal opening extending therethrough and an inner surface for receiving a gripping member. The inner surface of the bowl is inclined at an angle A b  relative to a longitudinal axis of the tubular. The gripping member is movable along the surface of the bowl for engaging the tubular and has an outer surface inclined at an angle A s  relative to the longitudinal axis of the tubular. A s  is greater than A b .  
         [0014]     In another embodiment, an apparatus for supporting a tubular is provided. The apparatus includes a bowl having a longitudinal opening extending therethrough and an inner surface for receiving a gripping member. The gripping member is movable along the surface of the bowl for engaging the tubular. The gripping member includes a die having teeth for engaging the tubular and disposed along a length of the gripping member. The die has a tapered thickness.  
         [0015]     In another embodiment, an apparatus for supporting a tubular is provided. The apparatus includes a bowl having a longitudinal opening extending therethrough and an inner surface for receiving a gripping member. The gripping member is movable along the surface of the bowl for engaging the tubular. The apparatus further includes means for distributing stress substantially evenly along a length of the tubular in contact with the gripping member.  
         [0016]     In another embodiment, an apparatus for supporting a tubular is provided. The apparatus includes at least one slip moveable along a surface of a support and having a first surface and an opposite gripping surface. The apparatus further includes a die having teeth for engaging the tubular, the die disposed in a slot formed in the gripping surface. The apparatus further includes the support, wherein: the first surface and the support surface are configured so that the gripping member will wedge between the support and the tubular, and the die and the slot are configured so that the die may rotate within the slot to facilitate engagement with the tubular.  
         [0017]     In another embodiment, a method for manufacturing an apparatus for supporting a tubular is provided. The method includes providing the apparatus, including: at least one slip moveable along a surface of a support and having a first surface and an opposite gripping surface for engaging the tubular; and the support, wherein: the first surface and the support surface are configured so that the gripping member will wedge between the support and the tubular, and the apparatus is configured so that an upper portion of the gripping surface will engage the tubular before the remainder of the gripping surface engages the tubular. The method further includes using the apparatus as a spider, elevator, liner hanger, plug, or gripping apparatus of a top drive casing make up unit.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0019]      FIG. 1  is an isometric view of a gripping apparatus, according to one embodiment of the present invention.  FIG. 1A  is an isometric view of one of the slips used in the spider of  FIG. 1 .  
         [0020]      FIG. 2  is a simplified sectional view of the spider of  FIG. 1 .  FIGS. 2A and 2C  are details of  FIG. 2  showing inclination angles of each slip and the bowl in a prior art spider and a spider according to one embodiment of the present invention, respectively.  FIGS. 2B and 2D  are plots of pipe stress versus longitudinal position of the tubular along the slips in a prior art spider and a spider according to one embodiment of the present invention, respectively.  
         [0021]      FIG. 3  is a sectional view of a die according to an alternative embodiment of the present invention.  
         [0022]      FIGS. 4A and 4B  are various views of another alternative embodiment of the present invention.  FIGS. 4A  is an isometric view of a slip.  FIG. 4B  is an isometric view of a bowl section.  
         [0023]      FIG. 5  is a top view of a slip according to another alternative embodiment of the present invention.  FIG. 5A  is a top view of a die, a plurality of which is received by the slip.  
         [0024]      FIG. 6A  is an isometric view of the spider of  FIG. 1  fitted with an elevator ring and bails for use with a top drive system or other hoisting device.  FIG. 6B  is a front view of  FIG. 6A .  
     
    
     DETAILED DESCRIPTION  
       [0025]      FIG. 1  is an isometric view of a gripping apparatus, according to one embodiment of the present invention. As shown, the gripping apparatus is a flush mounted spider  5  disposable within a rotary table (not shown). Alternatively, the spider  5  may be fitted for use in an elevator. Additionally, embodiments of the invention can be utilized in any well known apparatus that is dependent upon a slip member and a supporting surface, like a cone to retain the weight of a tubular string in a wellbore or at the surface of a well. Additionally, embodiments of the invention can be utilized in a top drive system used for drilling with casing. More specifically, embodiments can be used in a top drive casing make up system that grips the casing either by the inside or outside of the casing.  
         [0026]     The spider  5  includes a body, i.e. bowl  25 , for housing one or more gripping members, i.e. slips  20 , and a cover assembly  15  for the bowl  25 . The bowl  25  of the spider  5  is formed by pivotally coupling two sections  25   a,b  using one or more connectors, preferably hinges  35  formed on both sides of each body section, used to couple the two body sections together. Alternatively, the body sections  25   a,b  may be hinged on one side and selectively locked together on the other side. A hole is formed through each hinge  35  to accommodate a pin  40  (only one shown) to couple the bowl sections  25   a,b  together.  
         [0027]     The bowl  25  of the spider  5  includes one or more guide keys  45  (only one shown) for guiding the axial movement of a slip  20 . Each guide key  45  mates with a guide slot  46  formed longitudinally on the outer surface of the slip  20 . In this manner, the guide key  45  may maintain the path of a moving slip  20 . Furthermore, the guide key  45  prevents the slip  20  from rotating in the bowl  25  as it moves axially along the bowl  25 . Because the slip  20  cannot rotate within the bowl  25 , the spider  5  may be used as a back up torque source during the make up or break out of pipe connections.  
         [0028]     A flange  30  is formed on an upper portion of each of the bowl sections  25   a,b  for connection to the cover assembly  15 . An abutment, i.e. block  50  (only one shown), is attached to a lower portion of each flange  30  of the bowl sections  25   a,b.  The blocks  50  are designed to mate with slots formed in the rotary table (not shown). The blocks  50  allow torque to be reacted between the spider  5  and the rotary table. As a result, the spider  5  is prevented from rotating inside the rotary table when it is used as a back up torque source during the make up or break out of pipe connections.  
         [0029]     The spider  5  includes a leveling ring  55  for coupling the slips  20  together and synchronizing their vertical movement. The leveling ring  55  includes one or more guide bearings  60  extending radially from the leveling ring  55 . Preferably, the leveling ring  55  has four guide bearings  60  (three are shown) equally spaced apart around the circumference of the leveling ring  55 . For each guide bearing  60 , there is a corresponding guide track  65  formed on the inner wall of the upper portion of the bowl  25 . The guide track  65  directs the vertical movement of the leveling ring  55  and prevents the leveling ring  55  from rotating. Furthermore, the guide track  65  helps to center a tubular  90  (see  FIG. 2 ) inside the spider  5  and provides better contact between the slips  20  and the tubular.  
         [0030]     A piston and cylinder assembly  70  is attached below each of the guide bearings  60  and is associated with a respective slip  20 . The slips  20  will be disposed on a surface of the bowl  25  and will be moved along the bowl  25  by the piston and cylinder assembly  70 . An outer surface of each of the slips  20  is inclined and includes a guide slot  46  for mating with the respective guide key  45  of the bowl  25 . During operation, the piston and cylinder assembly  70  may lower the slip  20  along the incline of the bowl  25 . In turn, the incline directs the slip  20  radially toward the center of the spider  5 , thereby moving the slip  20  into contact with the tubular  90 . To release the pipe, the piston and cylinder  70  is actuated to move the slip  20  up the incline and away from the pipe.  
         [0031]     The cover assembly  15  includes two separate sections, each attached above a respective bowl section  25   a,b.  The sectioned cover assembly  15  allows the bowl sections  25   a,b  of the spider  10  to open and close without removing the cover assembly  15 . The sections of the cover assembly  15  form a hole whose center coincides with the center of the body  10 . The cover assembly  15  includes one or more guide rollers  80  to facilitate the movement and centering of the tubular  90  in the spider  5 . Preferably, the guide rollers  80  are attached below the cover assembly  15  and are adjustable. The guide rollers  80  may be adjusted radially to accommodate tubulars of various sizes. Alternatively, instead of guide rollers  80 , an adapter plate (not shown) having a hole sized for a particular tubular may be attached to each section of the cover assembly  15  to facilitate the movement and centering of the tubular.  
         [0032]      FIG. 1A  is an isometric view of one of the slips  20  used in the spider  5 . The slip  20  includes an outer member  20   a  having an inclined outer surface which corresponds with an inclined inner surface of the bowl  25 . Coupled to the outer member  20   a  is an inner member  20   b  which has a curved inner surface to accommodate the tubular  90 . One or more hardened metal dies  20   c  having teeth for engaging the tubular  90  are coupled to an inner surface of the inner member  20   b.    
         [0033]     In operation, the spider  5  is flush mounted in rotary table. Before receiving the tubular  90 , the guide rollers  80  are adjusted to accommodate the incoming tubular. Initially, the slips  20  are in a retracted position on the bowl  25 . After the tubular  90  is in the desired position in the spider  5 , the piston and cylinder assembly  70  is actuated to move the slips  20  down along the incline of the bowl  25 . The slips  20  are guided by the guide keys  45  disposed on the bowl  25 . The incline causes the slips  20  to move radially toward the tubular  90  and contact the tubular. Thereafter, the make up/break up operation is performed. To release the slips  20  from the tubular  90 , the piston and cylinder assembly  70  is actuated to move the slips  20  up along the incline, thereby causing the slips  20  to move radially away from the tubular.  
         [0034]      FIG. 2  is a simplified sectional view of the spider  5 . The slips  20  of spider  5  are shown engaging the tubular  90  which is part of a string of tubulars.  FIGS. 2A and 2C  are details of  FIG. 2  showing inclination angles, relative to a longitudinal axis of the tubular  90 , of each slip  20  and the bowl  25  in a prior art spider and the spider  5 , respectively.  FIGS. 2B and 2D  are plots of pipe stress versus longitudinal position of the tubular  90  along the slips  20  in a prior art spider and the spider  5 , respectively.  
         [0035]      FIG. 2A  shows that an inclination angle  95  is the same for both the slips and the bowl.  FIG. 2B  shows the resulting stress distribution along the length of the pipe in contact with the slips. Engineering calculations and finite element analysis show that the stress is concentrated on the lower section of the slips that are engaged with the tubular. This stress concentration is caused by the combination of radial stress that is generated by the slips engaging the tubular with axial stresses produced by the weight of the string. Thus, the stress distribution is non-uniform and the stress increases towards a lower end of the tubular  90 .  
         [0036]      FIG. 2C  shows a design that more evenly distributes the stress distribution along the length of the tubular  90  in contact with the dies  20   c  of the slips  20 . Each slip  20  has an inclination angle  95   s  that is greater than an inclination angle  95   b  of the bowl. Preferably, the difference between slip angle  95   s  and bowl angle  95   b  is less than 1 degree, more preferably less than one-quarter of a degree, and most preferably less than or equal to about one-eighth of a degree. This difference results in an upper portion of each of the dies  20   c  contacting the tubular  90  before the rest of each of the dies.  
         [0037]     As the weight of the tubular  90  is transferred to the spider  5 , the weight of the tubular will cause the upper portions of the dies  20   c  to locally deform or penetrate the outer surface of the tubular, thereby allowing the lower portions of the dies  20   c  to contact the tubular. This penetration causes more of the radial force, generated by the interaction of the slips  20  with the bowl  25 , to be exerted on the upper portion of the tubular  90  while allowing the tensile force, generated by the weight of the string, to be exerted on the lower portion of the tubular  90 .  FIG. 2D  shows the resulting stress distribution on the pipe is uniform or substantially uniform and the stress is substantially less than the maximum stress of the prior art configuration. The result is that for a given tubular  90 , the spider  5  may handle more weight or a longer string of tubulars before crushing the tubular than the prior art design.  
         [0038]     According to an alternative embodiment (not shown) of the present invention, an outer surface of each slip  20  may be curved instead of inclined so that an upper portion of each of the dies  20   d  contacting the tubular  90  before the rest of each of the dies  20   d,  thereby equally or substantially equally distributing the stress along the tubular  90 . Preferably, the outer surface is concave.  
         [0039]      FIG. 3  is a sectional view of a die  20   d  according to an alternative embodiment of the present invention. Instead of the slip angle  95   s  being greater than the bowl angle  95   b,  the thickness of the die  20   d  increases towards an upper end of each of the slips  20 . As with the embodiment shown in  FIGS. 1 and 2 C, using the dies  20   d,  in place of the mismatched angles  95   b,s,  would result in an upper portion of each of the dies  20   d  contacting the tubular  90  before the rest of each of the dies  20   d,  thereby equally or substantially equally distributing the stress along the tubular  90 .  
         [0040]      FIGS. 4A and 4B  are various views of another alternative embodiment of the present invention.  FIGS. 4A  is an isometric view of a slip  420 .  FIG. 4B  is an isometric view of a bowl section  425 . The slip  420  includes an outer member  420   a.  Coupled to the outer member  420   a  is an inner member  420   b  which has a curved inner surface (not shown, see member  20   b  shown in  FIG. 1A ) to accommodate the tubular  90 . Dies of the slip  420  are also not shown; however, they may be similar to the dies  20   c  shown in  FIG. 1A . The bowl section  425  includes a plurality of slots  402  formed in an inner surface thereof, each of which will receive a slip  420 . The outer member  420   a  has an inclined outer surface which corresponds with an inclined facing surface of each of the slots  402 .  
         [0041]     Similar to the embodiments shown in  FIGS. 1 and 2 C, the outer surface of the outer member  420   a  has an inclination angle  495   s  that is greater than an inclination angle  495   b  of the slots  402 , thereby equally or substantially equally distributing the stress along the tubular  90 . The difference between this embodiment and that of  FIGS. 1 and 2 C is that the outer surface of the outer member  420   a  is flat or substantially flat along a circumferential direction because of the slots  402 , which are also flat or substantially flat in a circumferential direction, whereas the outer surface of the outer member  20   a  is circumferentially curved to accommodate the circumferential curvature of the bowl  25 .  
         [0042]     According to another alternative embodiment (not shown) of the present invention, the height of the die teeth may vary along the length of the die so that the teeth on an upper portion of each of the dies contact the tubular before the teeth on the rest of each of the dies, thereby equally or substantially equally distributing the stress along the tubular.  
         [0043]      FIG. 5  is a top view of a slip  520  according to another alternative embodiment of the present invention.  FIG. 5A  is a top view of a die  520   c,  a plurality of which is received by the slip  520 . Formed in an inner surface of the inner member  520   b  is a plurality of slots  520   d.  Received in each of the slots  520   d  is one of the dies  520   c.  An inner surface of each die  520   c  is rounded so that the dies may rotate slightly within the slots  520   d  to improve gripping of the tubular  90 , especially for tubulars  90  with irregular cross sections. Alternatively, a facing surface of each slot  520   d  may be rounded instead of the inner surface of each die  520   c.  This rounded die  520   c  or slip slot  520   d  embodiment may be implemented in the embodiments shown in  FIGS. 1 and 2 C,  3 , and  4 .  
         [0044]      FIG. 6A  is an isometric view of the spider  5  of  FIG. 1  fitted with an elevator ring  605  and bails  615  for use with a top drive system (not shown) or other hoisting device.  FIG. 6B  is a front view of  FIG. 6A . The blocks  50  have been removed from the flanges  30 . The elevator ring slides over the bowl  25  from the bottom side until it abuts the flange  30 . The elevator ring has a pair of upper  605   a  and lower  605   b  brackets formed thereon. Each bracket has a hole for receiving a connector, such as a bolt. The upper brackets  605   a  are formed to each receive a loop  615   a  of each of the bails  615 . A “J” shaped bracket  610  is then coupled to each pair of upper  605   a  and lower  605   b  brackets by bolts to secure each loop  615   a  in place. The bails  615  are then attached to a body of a top drive system, traveling block, or other hoisting device.  
         [0045]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.