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CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/165,661, filed on Jun. 24, 2005, issuing as U.S. Pat. No. 7,699,121, which is a continuation-in-part of U.S. patent application Ser. No. 11/040,453, filed on Jan. 20, 2005, issued as U.S. Pat. No. 7,096,977, which is a continuation of U.S. patent application Ser. No. 10/189,355, filed on Jul. 3, 2002, issued as U.S. Pat. No. 6,938,709, which is a continuation of U.S. patent application Ser. No. 09/518,122, filed Mar. 3, 2000, issued as U.S. Pat. No. 6,443,241, which claims priority under 35 
         [0002]    U.S.C. §119(e) to U.S. Provisional Patent Application No. 60/122,915, filed on Mar. 5, 1999. 
     
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
       [0003]    This invention relates to well drilling operations and, more particularly, to a device for assisting in the assembly of pipe strings, such as casing strings, drill strings and the like. 
       2. Description of the Related Art 
       [0004]    The drilling of oil wells involves assembling drill strings and casing strings, each of which comprises a plurality of elongated, heavy pipe segments extending downwardly from an oil drilling rig into a hole. The drill string consists of a number of sections of pipe which are threadedly engaged together, with the lowest segment (i.e., the one extending the furthest into the hole) carrying a drill bit at its lower end. Typically, the casing string is provided around the drill string to line the well bore after drilling the hole and to ensure the integrity of the hole. The casing string also consists of a plurality of pipe segments which are threadedly coupled together and formed with through passages sized to receive the drill string and/or other pipe strings. 
         [0005]    The conventional manner in which plural casing segments are coupled together to form a casing string is a labor-intensive method involving the use of a “stabber” and casing tongs. The stabber is manually controlled to insert a segment of casing into the upper end of the existing casing string, and the tongs are designed to engage and rotate the segment to threadedly connect it to the casing string. While such a method is effective, it is cumbersome and relatively inefficient because the procedure is done manually. In addition, the casing tongs require a casing crew to properly engage the segment of casing and to couple the segment to the casing string. Thus, such a method is relatively labor-intensive and therefore costly. Furthermore, using casing tongs requires the setting up of scaffolding or other like structures, and is therefore inefficient. 
         [0006]    Accordingly, it will be apparent to those skilled in the art that there continues to be a need for a device for use in a drilling system which utilizes an existing top drive assembly to efficiently assemble casing and/or drill strings, and which positively engages a pipe segment to ensure proper coupling of the pipe segment to a pipe string. The present invention addresses these needs and others. 
       SUMMARY OF THE INVENTION 
       [0007]    Briefly, and in general terms, the present invention is directed to a pipe running tool for use in drilling systems and the like to assemble casing and/or drill strings. The pipe running tool is coupled to an existing top drive assembly which is used to rotate a drill string, and includes a powered elevator that is powered into an engaged position to securely engage a pipe segment, for example, a casing segment. Because the elevator is powered into the engaged position, the pipe segment may be properly coupled to an existing pipe string using the top drive assembly. 
         [0008]    The system of the present invention in one illustrative embodiment is directed to a pipe running tool mountable on a rig and including: a top drive assembly adapted to be connected to the rig for vertical displacement of the top drive assembly relative to the rig, the top drive assembly including a drive shaft, the top drive assembly being operative to rotate the drive shaft; and a lower pipe engagement assembly including a central passageway sized for receipt of the pipe segment, the lower pipe engagement assembly including a powered engagement device that is powered to an engaged position to securely and releasably grasp the pipe segment, the lower pipe engagement assembly being in communication with the drive shaft, whereby actuation of the top drive assembly causes the lower pipe engagement assembly to rotate. 
         [0009]    In another illustrative embodiment, the present invention is directed to a method of assembling a pipe string, including the steps of: actuating a lower pipe engagement assembly to releasably engage a pipe segment; lowering a top drive assembly to bring the pipe segment into contact with a pipe string; monitoring the load on the pipe string; actuating a load compensator to raise the pipe segment a selected distance relative to the pipe string, if the load on the pipe string exceeds a predetermined threshold value; and actuating the top drive assembly to rotate the pipe segment to threadedly engage the pipe segment and pipe string. 
         [0010]    Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the features of the present invention. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is an elevated side view of a drilling rig incorporating a pipe running tool according to one illustrative embodiment of the present invention; 
           [0012]      FIG. 2  is a side view, in enlarged scale, of the pipe running tool of  FIG. 1 ; 
           [0013]      FIG. 3  is a cross-sectional view taken along the line  3 - 3  of  FIG. 2 ; 
           [0014]      FIG. 4  is a cross-sectional view taken along the line  4 - 4  of  FIG. 2 ; 
           [0015]      FIG. 5A  is a cross-sectional view taken along the line  5 - 5  of  FIG. 4  and showing a spider\elevator in a disengaged position; 
           [0016]      FIG. 5B  is a cross-sectional view similar to  FIG. 5A  and showing the spider\elevator in an engaged position; 
           [0017]      FIG. 6  is a block diagram of components included in one illustrative embodiment of the invention; and 
           [0018]      FIG. 7  is a side view of another illustrative embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    In the following detailed description, like reference numerals will be used to refer to like or corresponding elements in the different figures of the drawings. Referring now to  FIGS. 1 and 2 , there is shown a pipe running tool  10  depicting one illustrative embodiment of the present invention, which is designed for use in assembling pipe strings, such as drill strings, casing strings, and the like. As shown for example in  FIG. 2 , the pipe running tool  10  comprises, generally, a frame assembly  12 , a rotatable shaft  14 , and a lower pipe engagement assembly  16  that is coupled to the rotatable shaft  14  for rotation therewith. The pipe engagement assembly  16  is designed for selective engagement of a pipe segment  11  (as shown for example in  FIGS. 1 ,  2 , and  5 A) to substantially prevent relative rotation between the pipe segment  11  and the pipe engagement assembly  16 . As shown for example in  FIG. 1 , the rotatable shaft  14  is designed for coupling with a top drive output shaft  28  from an existing top drive  24 , such that the top drive  24 , which is normally used to rotate a drill string to drill a well hole, may be used to assemble a pipe string, for example, a casing string or a drill string, as is described in greater detail below. 
         [0020]    As show, for example, in  FIG. 1 , the pipe running tool  10  is designed for use, for example, in a well drilling rig  18 . A suitable example of such a rig is disclosed in U.S. Pat. No. 4,765,401 to Boyadjieff, which is expressly incorporated herein by reference as if fully set forth herein. As shown in  FIG. 1 , the well drilling rig  18  includes a frame  20  and a pair of guide rails  22  along which a top drive assembly, generally designated  24 , may ride for vertical movement relative to the well drilling rig  18 . The top drive assembly  24  is preferably a conventional top drive used to rotate a drill string to drill a well hole, as is described in U.S. Pat. No. 4,605,077 to Boyadjieff, which is expressly incorporated herein by reference. The top drive assembly  24  includes a drive motor  26  and a top drive output shaft  28  extending downwardly from the drive motor  26 , with the drive motor  26  being operative to rotate the drive shaft  28 , as is conventional in the art. The well drilling rig  18  defines a drill floor  30  having a central opening  32  through which a drill string and/or casing string  34  is extended downwardly into a well hole. 
         [0021]    The rig  18  also includes a flush-mounted spider  36  that is configured to releasably engage the drill string and/or casing string  34  and support the weight thereof as it extends downwardly from the spider  36  into the well hole. As is well known in the art, the spider  36  includes a generally cylindrical housing which defines a central passageway through which the pipe string  34  may pass. The spider  36  includes a plurality of slips which are located within the housing and are selectively displaceable between disengaged and engaged positions, with the slips being driven radially inwardly to the respective engaged positions to tightly engage the pipe segment and thereby prevent relative movement or rotation of the pipe segment and the spider housing. The slips are preferably driven between the disengaged and engaged positions by means of a hydraulic or pneumatic system, but may be driven by any other suitable means. 
         [0022]    Referring primarily to  FIG. 2 , the pipe running tool  10  includes the frame assembly  12 , which comprises a pair of links  40  extending downwardly from a link adapter  42 . The link adapter  42  defines a central opening  44  through which the top drive output shaft  28  may pass. Mounted to the link adapter  42  on diametrically opposed sides of the central opening  44  are respective upwardly extending, tubular members  46  ( FIG. 1 ), which are spaced a predetermined distance apart to allow the top drive output shaft  28  to pass therebetween. The respective tubular members  46  connect at their upper ends to a rotating head  48 , which is connected to the top drive assembly  24  for movement therewith. The rotating head  48  defines a central opening (not shown) through which the top drive output shaft  28  may pass, and also includes a bearing (not shown) which engages the upper ends of the tubular members  46  and permits the tubular members  46  to rotate relative to the rotating head body, as is described in greater detail below. 
         [0023]    The top drive output shaft  28  terminates at its lower end in an internally splined coupler  52  which is engaged to an upper end (not shown) of the lower drive shaft  14  which is formed to complement the splined coupler  52  for rotation therewith. Thus, when the top drive output shaft  28  is rotated by the top drive motor  26 , the lower drive shaft  14  of the pipe running tool  10  is also rotated. It will be understood that any suitable interface may be used to securely engage the top and lower drive shafts together. 
         [0024]    In one illustrative embodiment, the lower drive shaft  14  of the pipe running tool  10  is connected to a conventional pipe handler, generally designated  56 , which may be engaged by a suitable torque wrench (not shown) to rotate the lower drive shaft  14  and thereby make and break connections that require very high torque, as is well known in the art. 
         [0025]    The lower drive shaft  14  of the pipe running tool is also formed with a splined segment  58 , which is slidably received in an elongated, splined bushing  60  which serves as an extension of the lower drive shaft  14  of the pipe running tool  10 . The drive shaft  14  and the bushing  60  are splined to provide for vertical movement of the shaft  14  relative to the bushing  60 , as is described in greater detail below. It will be understood that the splined interface causes the bushing  60  to rotate when the lower drive shaft  14  of the pipe running tool  10  rotates. 
         [0026]    The pipe running tool  10  further includes the lower pipe engagement assembly  16 , which in one embodiment comprises a torque transfer sleeve  62  (as shown for example in  FIG. 2 ), which is securely connected to a lower end of the bushing  60  for rotation therewith. The torque transfer sleeve  62  is generally annular and includes a pair of upwardly projecting arms  64  on diametrically opposed sides of the sleeve  62 . The arms  64  are formed with respective horizontal through passageways (not shown) into which are mounted respective bearings (not shown) which serve to journal a rotatable axle  70  therein, as described in greater detail below. The torque transfer sleeve  62  connects at its lower end to a downwardly extending torque frame  72  in the form of a pair of tubular members  73 , which in turn is coupled to a spider\elevator  74  which rotates with the torque frame  72 . It will be apparent that the torque frame  72  may have any one of a variety of structures, such as a plurality of tubular members, a solid body, or any other suitable structure. 
         [0027]    The spider\elevator  74  is preferably powered by a hydraulic or pneumatic system, or alternatively by an electric drive motor or any other suitable powered system. As shown in  FIGS. 5A and 5B , the spider\elevator includes a housing  75  which defines a central passageway  76  through which the pipe segment  11  may pass. The spider\elevator  74  also includes a pair of hydraulic or pneumatic cylinders  77  with displaceable piston rods  78  ( FIGS. 5A and 5B ) which are connected through suitable pivotable linkages  79  to respective slips  80 . The linkages  79  are pivotally connected to both the top ends of the piston rods  78  and to the top ends of the slips  80 . The slips  80  include generally planar front gripping surfaces  82 , and specially contoured rear surfaces  84  which are designed with such a contour to cause the slips  80  to travel between respective radially outwardly disposed, disengaged positions, and radially inwardly disposed, engaged positions. The rear surfaces of the slips  80  travel along respective downwardly and radially inwardly projecting guiding members  86  which are complementarily contoured and securely connected to the spider body. The guiding members  86  cooperate with the cylinders  77  and linkages  79  to cam the slips  80  radially inwardly and force the slips  80  into the respective engaged positions. Thus, the cylinders  77  (or other actuating means) may be empowered to drive the piston rods  78  downwardly, causing the corresponding linkages  79  to be driven downwardly and therefore force the slips  80  downwardly. The surfaces of the guiding members  86  are angled to force the slips  80  radially inwardly as they are driven downwardly to sandwich the pipe segment  11  between them, with the guiding members  86  maintaining the slips  80  in tight engagement with the pipe segment  11 . To release the pipe segment  11 , the cylinders  77  are operated in reverse to drive the piston rods  78  upwardly, which draws the linkages  79  upwardly and retracts the respective slips  80  back to their disengaged positions to release the pipe segment  11 . The guiding members  86  are preferably formed with respective notches  81  which receive respective projecting portions  83  of the slips  80  to lock the slips  80  in the disengaged position ( FIG. 5A ). 
         [0028]    The spider\elevator  74  further includes a pair of diametrically opposed, outwardly projecting ears  88  formed with downwardly facing recesses  90  sized to receive correspondingly formed, cylindrical members  92  at the bottom ends of the respective links  40 , and thereby securely connect the lower ends of the links  40  to the spider\elevator  74 . The ears  88  may be connected to an annular sleeve  93  which is received over the housing  75 , or may be integrally formed with the housing. 
         [0029]    In one illustrative embodiment, the pipe running tool  10  includes a load compensator, generally designated  94 . In one embodiment, the load compensator  94  preferably is in the form of a pair of hydraulic, double rodded cylinders  96 , each of which includes a pair of piston rods  98  that are selectively extendable from, and retractable into, the cylinders  96 . Upper ends of the rods  98  connect to a compensator clamp  100 , which in turn is connected to the lower drive shaft  14  of the pipe running tool  10 , while lower ends of the rods  98  extend downwardly and connect to a pair of ears  102  which are securely mounted to the bushing  60 . The hydraulic cylinders  96  may be actuated to draw the bushing  60  upwardly relative to the lower drive shaft  14  of the pipe running tool  10  by applying a pressure to the cylinders  96  which causes the upper ends of the piston rods  98  to retract into the respective cylinder bodies  96 , with the splined interface between the bushing  60  and the lower drive shaft  14  allowing the bushing  60  to be displaced vertically relative to the shaft  14 . In that manner, the pipe segment  11  carried by the spider\elevator  74  may be raised vertically to relieve a portion or all of the load applied to the pipe segment  11 , as is described in greater detail below. As is shown in  FIG. 2 , the lower ends of the rods  98  are at least partially retracted, resulting in the majority of the load from the pipe running tool  10  is assumed by the top drive output shaft  28 . In addition, when a load above a pre-selected maximum is applied to the pipe segment  11 , the cylinders  96  will automatically retract the load to prevent the entire load from being applied to the threads of the pipe segment. 
         [0030]    In one embodiment, the pipe running tool  10  still further includes a hoist mechanism, generally designated  104 , for hoisting a pipe segment  11  upwardly into the spider\elevator  74 . In the embodiment of  FIG. 2 , the hoist mechanism  104  is disposed off-axis and includes a pair of pulleys  106  carried by the axle  70 , the axle  70  being journaled into the bearings in respective through passageways formed in the arms  64 . The hoist mechanism  104  also includes a gear drive, generally designated  108 , that may be selectively driven by a hydraulic motor  111  or other suitable drive system to rotate the axle  70  and thus the pulleys  106 . The hoist may also include a brake  115  to prevent rotation of the axle  70  and therefore of the pulleys  106  and lock them in place, as well as a torque hub  116 . Therefore, a pair of chains, cables, or other suitable, flexible means may be run over the respective pulleys  106 , extended through a chain well  113 , and engaged to the pipe segment  11 , and the axle  70  is then rotated by a suitable drive system to hoist the pipe segment  11  vertically and up into position with the upper end of the pipe segment  11  extending into the spider\elevator  74 . 
         [0031]    In one embodiment, as shown in  FIG. 1 , the pipe running tool  10  preferably further includes an annular collar  109  which is received over the links  40  and which maintains the links  40  locked to the ears  88  and prevents the links  40  from twisting and/or winding. 
         [0032]    In use, a work crew may manipulate the pipe running tool  10  until the upper end of the tool  10  is aligned with the lower end of the top drive output shaft  28 . The pipe running tool  10  is then raised vertically until the splined coupler  52  at the lower end of the top drive output shaft  28  is engaged to the upper end of the lower drive shaft  14  of the pipe running tool  10  and the links  40  of the pipe running tool  10  are engaged with the ears  88  . The work crew may then run a pair of chains or cables over the respective pulleys  106  of the hoist mechanism  104 , connect the chains or cables to a pipe segment  11 , engage a suitable drive system to the gear  108 , and actuate the drive system to rotate the pulleys  106  and thereby hoist the pipe segment  11  upwardly until the upper end of the pipe segment  11  extends through the lower end of the spider\elevator  74 . The spider\elevator  74  is then actuated, with the hydraulic cylinders  77  and guiding members  86  cooperating to forcibly drive the respective slips  80  into the engaged positions ( FIG. 5B ) to positively engage the pipe segment  11 . The slips  80  are preferably advanced to a sufficient extent to prevent relative rotation between the pipe segment  11  and the spider\elevator  74 , such that rotation of the spider\elevator  74  translates into rotation of the pipe segment  11 . 
         [0033]    The top drive assembly  24  is then lowered relative to the frame  20  by means of a top hoist  25  to drive the threaded lower end of the pipe segment  11  into contact with the threaded upper end of the pipe string  34  ( FIG. 1 ). As shown in  FIG. 1 , the pipe string  34  is securely held in place by means of the flush-mounted spider  36  or any other suitable structure for securing the string  34  in place, as is well known to those skilled in the art. Once the threads of the pipe segment  11  are properly mated with the threads of the pipe string  34 , the top drive motor  26  is then actuated to rotate the top drive output shaft  28 , which in turn rotates the lower drive shaft  14  of the pipe running tool  10  and the spider\elevator  74 , which causes the coupled pipe segment  11  to rotate and thereby be threadedly engaged to the pipe string  34 . 
         [0034]    In one embodiment, the pipe segment  11  is intentionally lowered until the lower end of the pipe segment  11  rests on the top of the pipe string  34 . The load compensator  94  is then actuated to drive the bushing  60  upwardly relative to the lower drive shaft  14  of the pipe running tool  10  via the splined interface between the two. The upward movement of the bushing  60  causes the spider\elevator  74  and therefore the coupled pipe segment  11  to be raised, thereby reducing the weight on the threads of the pipe segment. In this manner, the load on the threads can be controlled by actuating the load compensator  94 . 
         [0035]    Once the pipe segment  11  is threadedly coupled to the pipe string  34 , the top drive assembly  24  is raised vertically to lift the entire pipe string  34 , which causes the flush-mounted spider  36  to disengage the pipe string  34 . The top drive assembly  24  is then lowered to advance the pipe string  34  downwardly into the well hole until the upper end of the top pipe segment  11  is close to the drill floor  30 , with the entire load of the pipe string being carried by the links  40  while the torque was supplied through shafts. The flush-mounted spider  36  is then actuated to engage the pipe string  11  and suspend it therefrom. The spider\elevator  74  is then controlled in reverse to retract the slips  80  back to the respective disengaged positions ( FIG. 5A ) to release the pipe string  11 . The top drive assembly  24  is then raised to lift the pipe running tool  10  up to a starting position (such as that shown in  FIG. 1 ) and the process may be repeated with an additional pipe segment  11 . 
         [0036]    Referring to  FIG. 6 , there is shown a block diagram of components included in one illustrative embodiment of the pipe running tool  10 . In this embodiment, the tool includes a conventional load cell  110  or other suitable load-measuring device mounted on the pipe running tool  10  in such a manner that it is in communication with the lower drive shaft  14  of the pipe running tool  10  to determine the load applied to the lower end of the pipe segment  11 . The load cell  110  is operative to generate a signal representing the load sensed, which in one illustrative embodiment is transmitted to a processor  112 . The processor  112  is programmed with a predetermined threshold load value, and compares the signal from the load cell  110  with that value. If the load exceeds the value, the processor then controls the load compensator  94  to draw upwardly a selected amount to relieve at least a portion of the load on the threads of the pipe segment  11 . Once the load is at or below the threshold value, the processor  112  controls the top drive assembly  24  to rotate the pipe segment  11  and thereby threadedly engage the pipe segment  11  to the pipe string  34 . While the top drive assembly  24  is actuated, the processor  112  continues to monitor the signals from the load cell  110  to ensure that the load on the pipe segment  11  does not exceed the threshold value. 
         [0037]    Alternatively, the load on the pipe segment  11  may be controlled manually, with the load cell  110  indicating the load on the pipe segment  11  via a suitable gauge or other display, with a work person controlling the load compensator  94  and top drive assembly  24  accordingly. 
         [0038]    Referring to  FIG. 7 , there is shown another preferred embodiment of the pipe running tool  200  of the present invention. The pipe running tool includes a hoisting mechanism  202  which is substantially the same as the hoisting mechanism  104  described above. A lower drive shaft  204  is provided and connects at its lower end to a conventional mud-filling device  206  which, as is known in the art, is used to fill a pipe segment  11 , for example, a casing segment, with mud during the assembly process. In one illustrative embodiment, the mud-filling device is a device manufactured by Davies-Lynch Inc. of Texas. 
         [0039]    The hoisting mechanism  202  supports a pair of chains  208  which engage a slip-type single joint elevator  210  at the lower end of the pipe running tool  200 . As is known in the art, the single joint elevator is operative to releasably engage a pipe segment  11 , with the hoisting mechanism  202  being operative to raise the single joint elevator and the pipe segment  11  upwardly and into the spider\elevator  74 . 
         [0040]    The tool  200  includes the links  40  which define the cylindrical lower ends  92  which are received in generally J-shaped cut-outs  212  formed in diametrically opposite sides of the spider\elevator  74 . 
         [0041]    From the foregoing, it will be apparent that the pipe running tool  10  efficiently utilizes an existing top drive assembly  24  to assemble a pipe string  11 , for example, a casing or drill string, and does not rely on cumbersome casing tongs and other conventional devices. The pipe running tool  10  incorporates the spider\elevator  74 , which not only carries pipe segments  11 , but also imparts rotation to them to threadedly engage the pipe segments  11  to an existing pipe string  34 . Thus, the pipe running tool  10  provides a device which grips and torques the pipe segment  11 , and which also is capable of supporting the entire load of the pipe string  34  as it is lowered down into the well hole. 
         [0042]    While several forms of the present invention have been illustrated and described, it will be apparent to those of ordinary skill in the art that various modifications and improvements can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.

Summary:
A system for coupling a pipe segment to a pipe string is provided that includes a top drive assembly having a threaded output shaft; and a pipe running tool threadingly coupled to the threaded output shaft of the top drive assembly such that the primary load of the pipe running tool is supported by the threads of the output shaft of the top drive assembly, and wherein the pipe running tool is rotatable by the output shaft and further includes a pipe engaging portion for grippingly engaging the pipe segment sufficient to transmit a torque from the top drive output shaft to the pipe segment.